High Mileage 996 Engines - Page 5 - Porsche General - PistonHeads UK

Hi all. I've read quite a few threads about a small proportion of 996 engines succumbing to various ailments resulting in the need for costly repairs or replacement but are there many examples of these engines reaching high mileages without much trouble? I was thinking of upwards of 100k. What about the rest of the main mechanical items? Steve.

You have the weekend which still wont give you enough time to read all the posts on here regarding 996 / boxster engine problems. In a few lines, they nearly all have problems with the RMS (rear main seal)leaking oil, which depending on when noticed can lead to oil drips on the garage floor or total engine failure. Some early cars had problems with the liners which leads to engine failure unless very lucky. Before I get s gged off for talking bad about 996's I had 3 boxsters (all new) and a low milage C2, only the 98 C2 needed attention to the RMS. A very well respected Porsche dealer said to me when trying to px the C2 " its not a case of if they go wrong its when they go wrong, we have had them go pop at 8k miles and 108k miles you just dont know" Wouldnt stop me buying one but would want warranty of some kind again well covered on here. 100k+ ...... I would be thinking carefully

There are very occasional issues, but many many engines have passed 100k with no issues. I don't believe porsche are any worse than any other brand (BMW Vanos, Nissan GTR Gearboxes, Audi DRC, etc.), it's more that the cost is big when things go wrong and Porsche are not known for their helpfulness. Buy a warranty if you really want to sleep well at night (applies to any expensive car imho). Edit - brncrl will be along shortly, don't forget to ask him if he owns a porsche. Edited by noumenon on Friday 19th December 16:50

Stephen Pook said: Hi all. I've read quite a few threads about a small proportion of 996 engines succumbing to various ailments resulting in the need for costly repairs or replacement but are there many examples of these engines reaching high mileages without much trouble? I was thinking of upwards of 100k. What about the rest of the main mechanical items? Steve. I reckon I'd treat RMS as a service item. Aside from that I reckon time will show that motor to go 200k plus if looked after.

My 3.6 996 has covered 80K miles with no problems. I RMS replacement in that time

Huntsman said: Stephen Pook said: Hi all. I've read quite a few threads about a small proportion of 996 engines succumbing to various ailments resulting in the need for costly repairs or replacement but are there many examples of these engines reaching high mileages without much trouble? I was thinking of upwards of 100k. What about the rest of the main mechanical items? Steve. I reckon I'd treat RMS as a service item. Aside from that I reckon time will show that motor to go 200k plus if looked after. 200K ! i would like to see this.... Biggest mileage ive see on original engine was 120K Mike

sportsandclassic said: Biggest mileage ive see on original engine was 120K Mike And what state was it in?

sportsandclassic said: Huntsman said: Stephen Pook said: Hi all. I've read quite a few threads about a small proportion of 996 engines succumbing to various ailments resulting in the need for costly repairs or replacement but are there many examples of these engines reaching high mileages without much trouble? I was thinking of upwards of 100k. What about the rest of the main mechanical items? Steve. I reckon I'd treat RMS as a service item. Aside from that I reckon time will show that motor to go 200k plus if looked after. +1 200K ! i would like to see this.... Biggest mileage ive see on original engine was 120K Mike

Hi it snapped the timing chain ! Pistons picked up on 5 and 6 cylinders and alot of blow by past the rings.....big end bearings very out of shape ! Mike

sportsandclassic said: Hi it snapped the timing chain ! Pistons picked up on 5 and 6 cylinders and alot of blow by past the rings.....big end bearings very out of shape ! Mike Does the waterpumper sevice schedule mention ever replacing timing chains? Time will tell I guess as more get into big miles.

Huntsman said: sportsandclassic said: Hi it snapped the timing chain ! Pistons picked up on 5 and 6 cylinders and alot of blow by past the rings.....big end bearings very out of shape ! Mike Does the waterpumper sevice schedule mention ever replacing timing chains? Time will tell I guess as more get into big miles. Hello No interval on the timing chains...we have started changing them as a preventative measure by fitting split link chains which means we do nothave to strip the engine down to the crank shaft and as far as we know are the only place to offer this service by checking the timing of the cams with the porsche tester on 3.6L engines and see how much the variators are adjusting due to stretch in the chains....we beleive the chains are being over tensioned as they are of very good origin and quality.... Mike

Nearly 107,000 on mine and not using any oil or water. You won't get a warranty on anything over 9 years old now, but there are other options - such as Hartech. Oh, and don't forget to ask bcnrml how many miles his Porsche has done now;) Edited by kVA on Friday 19th December 23:08

Don't forget these figures will get distorted. As the purchase price becomes affordable people will stretch themselves to get one and will not be able to afford to maintain them properly. Then the s gging off begins.

Some early engines had a bigger hydraulic chain tensioner but that was quickly rectified by Porsche although I have not seen any evidence of the change being formally recorded. Similarly head sizes on head bolts being made bigger. Crankshaft to shell clearances are slightly higher than previous engines (probably to reflect the cracked con-rods being less accurate) and shell quality varioes and has been altered in later models. Baz

122k miles on my 996 tip. Original engine! I RMS repair. Jason

77k on my early 3.4 Manual... Using no oil or water between services in the 5k I have owned it and the temperatures still look good and performance is still awesome! Then again, I guess that actually makes mine quite low mileage as it will be less than 8k per annum on its 10th birthday? Also, no expense spared on maintenance and it is not thrashed/ abused.

There's a 2004 boxster 2.7 on autotrader that's got 140k on it. Though I guess the true intergalactic figures aren't generally put on the ad.

Its an odd one this how some cars do have problems and others dont, my dads 987 had problems at 29k miles, intermediate shaft went and flooded the garage out with quite a bit oil.. he had really looked after that car and never over revved it or drove it excessively hard, worked as a service manager so hes no mug when it comes to cars. Then there is my 986 which i reguarly gave the beans (always up to temperature first) right up to 50k miles and not even a RMS leak..nothing.

I will try and offer some explanations and answers to the various points made so far (and perhaps provide something for you to ponder over Christmas). Most high performance engines will need rebuilds at some time in their lives to maintain performance. Previous Porsche engines were generally manufactured to such a high standard they could be tuned up significantly without much increase in failure rates (i.e. 911's as the basic original design capacity grew from 2 to 3.6 litres, 924's and 944's to turbo's, and into the 968 etc and in all this Porsche made less and less profit until eventually it cost them more to manufacture than they sold for. This is because the "market" sets an acceptable price for volume sales of a product and basically they made too good a job - by "old fashioned methods" for the production costs that resulted and were unable to reinvest gradually/continually. The very fact that their "standard" engines could be "tuned up" without adverse consequences basically proved that they had been over engineered in the first place and the modern world simply cannot afford such extravagance - whoever you are and whatever you manufacture. The world has got better at making perfectly good cars (engines and gearboxes) for a lower cost but Porsche increasingly were unable to afford the transition to that new technology until they had to make a leap of faith to the new range of Boxster and 996 engines. They went overnight from far too over engineered, expensive engines to manufacture - to "up to date" engines made by the latest technology for a purpose and to a price. This sets a point in time at which things obviously changed - but without which Porsche would not now exist. The result is more powerful than before, less emissions, with a lot of good ideas and high quality parts but designed more for a price than just quality. When it came to more powerful examples this time (Gt's and turbocharged versions) Porsche already new that they would have to use better/different engine designs in some areas (rather than just uplift the power of the standard product) and did so and put up the cost accordingly. This time you paid extra for the basic engine that could provide extra performance (and IMHO quite rightly!). All this means they did the right thing and designed and made things to serve the purpose they were intended and the price they attracted. Unfortunately they had been so reliable before (as a result of the over engineering) people expected the same reliability. I think Porsche thought they had achieved that too because a lot of the design is actually very clever and has been done that way for long term life and rebuild potential (of which the steel reinforced crank carrier is a great example and the Lokasil bore lack of surface wear and good lubrication is another). But when you design such a high output power plant with lots of new ideas and for a price - there are inevitably a few weak spots that time reveals that perhaps could have been done a little better in the first place and a few new ideas that were not the best - as it turns out. The problems therefore split into 4 possible areas - (A) Those that were not the best design or production ideas (as it turns out), or new technology that hasn't quite worked as well as expected in practice - and (B) those that were the result of typical modern engine design practice that were always designed for the purpose intended - for a price and have a lifespan more typical of all other modern engines - and therefore that occasionally fail. (C) The fact that it may be financially beneficial (or a preference) for some places to recommend a new engine when in the past it would have been less expensive to simply repair the fault and rebuild the engine. (D) The emergence of the internet as a way of communicating product dissatisfaction that members of the public were previously largely unaware of. Looking at (A) the following come to mind. (1) The Lokasil bore idea provides a brilliant bore surface for a modest production cost - but needs sufficient aluminium wall thickness to prevent stretching and cracking. The Boxster up to (and including the 3.2S) were Ok but instead of increasing the wall thickness for the 3.4 and 3.6 engines - they kept the outside diameter the same and increased the bore - so making the wall thickness thinner and the bore became unstable and goes oval in time. They would not have expected this as it is probably a symptom of "metal matrix composites" which is too new a technology to anticipate. The benefits would have seemed to outweigh the possible problems although there are solutions that have not been taken up. Oval bores increase piston clearance (and eventually prevent good ring sealing until the blow by burns off the lubricant and the piston partially or wholly seizes) or they crack. We can re-round the bores and fit supporting rings to remove this problem. (2) The dreaded IMS bearing failures. In my view this was a poor design - and should have been picked up sooner and sorted out quicker and for too long blindly continued to use the same design for the primary source of the problem by shielding the bearing from a replenishing oil supply. We change the lubricating method and fit stronger spindles. (3) As with all other modern engines I have seen - the crankshaft shell bearings are thinner than could have been fitted into the space available - I am told to reduce friction and improve mpg (although I am sceptical about this explanation). Wider shells maintain vital oil pressure to critical parts longer and are therefore more reliable and probably cost no more. We have had wider undersize shells manufactured - currently under test - but they could have been fitted originally and probably would have extended crankshaft life - but this then opens up the debate about how long should the engine have been designed to last and what is an acceptable mileage for the cost and performance? (4) The RMS leak is not technically a serious reliability problem – rather more an inconvenience and could have been cured with a relatively simple re-design that was not forthcoming. (B) (1) Cracked jointed con rods and Nitrided crankshafts are a modern production method that is good and dramatically lowers costs - almost with 100% reliability. Without explaining why (it would take too long) - occasionally they don't last as long as parts made by the older and more expensive methods - and if this happens it is a cost you pay for buying a modern car for the price you pay for it. We are testing re-ground and re-hardened crankshafts but it will be a while before we can do enough testing to use them as a production option (2) Smaller chain driven sprockets (as fitted to modern engines) are cheaper to produce and take up less space but they load and wear chains more leading to occasional unreliability (although chain problems are extremely infrequent and the least of our concerns). New chains can be fitted during a rebuild or we can fit split link chains without stripping the engine. (3) Plastic pipes, inlet manifolds, oil separators, etc. These dramatically reduce production costs but deteriorate more with age and mileage than traditional designs - again visiting the cost/expectation argument - what was planned and what is acceptable? (C) Perhaps the biggest problem has been the reluctance to simply rebuild the engines. This has IMHO delayed the desire to learn about the shortcomings and redesign solutions. I am not suggesting this is wrong as it seems to be the modern way to address all product problems – but it has left owners with a harsh choice and a huge cost that has implied that the engines are poorly made (if they cannot be rebuilt) whereas in practice they are perfectly Ok to rebuild with very high reliability – if the desire is there to do it. Furthermore if rebuilding is an option it is inevitable that changes will be thought of at the same time to improve the resulting performance and longevity, whereas simply replacing the engine doesn’t promote the same incentives. It may well be that with main agent labour rates so relatively high - it is a better option for them to offer replacement engines (or it may be better financially for them to do so as they have lower recharge rates and a percentage of parts costs to consider in their internal costings). The engines are also more difficult to rebuild than traditional engines and less places seem to have undertaken it – so again – that option seems less well publicised and has created an impression that the engines need to be replaced (and therefore are really bad) – which is nonsense. (D) The internet has a lot to answer for. On the one hand it has provided an invaluable platform for people to communicate by – but on the other hand it seems to have encouraged some people to raise their own self esteem by posting as experts (when they are not) and this has resulted in a lot of arguments to rage that were traditionally only the province of debating societies and between people usually at least qualified to present a case. It is human nature anyway to have different opinions but the greatly increased and potentially Worldwide readership has raised the profile of disagreements and for some people the desperation to be seen to be right – which is unprecedented – hence the volatility of some of the arguments on here. Because we not only rebuild engines but also – in the process – improve all the known main weak spots (many of which we have not listed) and manage to do this for a price that is actually often less than most others are charging for 944’s, 968’s and air cooled 911’s – with exceptional reliability – from our point of view - these are all good engines that have a few relatively minor weak spots that can be improved or fixed and for a high performance engine the reliability rates are perfectly acceptable and rebuilds (if required) a reasonable alternative. Consequently we defend the general quality of the engines and are relaxed about the repair situation – in the relatively few cases we come across. We are bound in these circumstances to argue with those who criticise them unfairly – but only because – for us – they do not present a problem and are easy and relatively inexpensive to fix. Because we were probably first into rebuilding them commercially (and probably due to my background designing and manufacturing racing engines) we have managed to fix/re-use all the engines that come our way (in increasing numbers) for modest costs with good outcomes (despite most initially being condemned elsewhere and the only alternative then offered being a new replacement). However – for others unable to access our services – or fearful of the problem that has been relatively exaggerated by the recent and prolific use of internet forums – they may form the opposite conclusions. I guess it is all relative and depends where you are coming from – but there are a few facts that are indisputable. (1) Porsche could not have existed doing the same things again after the 1990’s and had to modernise production. (2) Porsche had to use modern production ideas and methods to survive and there is an inevitable consequence. (3) If the Internet had been active 20 or 30 years ago there would have been more criticism and awareness of other design/production failures in older examples. (4) If Porsche had simply tried to rebuild all engines first and been more generous with compensation/rebuild prices – the engines would not have got such a poor reputation (and they possibly might have introduced permanent remedies more quickly). (5) If you have a problem with your engine and have access to our services – or – if you find the idea of a rebuild for preventative maintenance (and the improvement of weak areas) acceptable (as it has been for all other models perhaps at slightly higher mileages) we can offer viable and reliable alternatives to a new engine with numerous rebuild options and technical changes. Perhaps the only thing Porsche did wrong in their desire to survive as a sports car manufacturer, was to do too good a job of the cost reduction exercise (and therefore make more profit than they expected) and then be reluctant to admit to the few shortcomings that resulted (by way of compensation or replacement engine prices) to preserve their previous reputation. For most people with engines under 100K - it is relatively no more expensive to repair an engine than invest in a premature rebuild to avoid a failure and so I think it is probably better to await the unlikely failure first (and this will be reinforced if our crankshaft repair methods prove reliable - as they should). The mileage at which it may be worth considering a preventative rebuild is difficult to establish. For Boxsters I guess it will end up being around 140K but for 996's it will probably be 100K or so. This allows that a few will fail before that and is trying to second guess the mileage that they can still be recovered from before wear and catastophic failures increase the costs too much. Happy Christmas everyone, Baz

Brilliant brilliant post Baz and a really good synopsis of all you'd need to know about why the 996 is what it is. Everydays a school day they say .. Loads of new info there for the digestion thereof! Seasons greetings by the way!

Top post. [+]

+1 has porsche now gone some way to addressing these issues with the gen 2 engine by doing away with the dreaded ims? Edited by mayes911 on Monday 22 December 16:15

....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas.

Cheers Baz, The preventative maintenance idea reminds me of my old E28 M5 that I happened to have when it needed it timing chains replaced etc at 120k. Expensive at the time but good peace of mind. Also echo question regarding if you have experience of any 997 engine issues and relative strengths.

madala said: ....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas. Try livin in Dublin

Ballcock said: madala said: ....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas. Try livin in Dublin Is it still full of kids on horses randomly darting out of side streets? It was last time I drove through it!

....Bally I know...and you drink Beamish....living in Dublin!!!!....sheesh....says it all...lol...;) To be honest living in West London I am somewhat spoilt for choice for good Indies..... Edited by madala on Monday 22 December 17:12 Edited by madala on Monday 22 December 17:12

my MK1 Gt3 has 88k miles, put out 361 bhp on a german Maha dyno in May! Doesnt use water, needs a pint of oil after driving to the Ring from Dublin and then 3 hard days lapping at the ring'..... I change the oil 3-4 times per year in engine and gearbox, OE airfilters and fuel filters.. Recently had the timing chain tensioners changed as a precaution. Mite have chain done soon..

Ballcock said: madala said: ....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas. Try livin in Dublin I go from Suffolk. Something like a 550 mile round trip.

noumenon said: Ballcock said: madala said: ....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas. Try livin in Dublin Is it still full of kids on horses randomly darting out of side streets? It was last time I drove through it! So it was you that ran over me young ones harse

Happy Christmas Baz. Makes a change to read a really informative and honest post. Normally posts that refer to the cost cutting exercises of Porsche are met with cries of disbelief. However you have put the point across in such an inoffensive way, no one should get upset. The harsh reality was that Porsche had no option but to reduce build costs in order to survive. In the process they made more money than they had hoped for and hopefully this has stood them in good stead to survive the current global econonic crisis.

Dave 321 said: my MK1 Gt3 has 88k miles, put out 361 bhp on a german Maha dyno in May! Doesnt use water, needs a pint of oil after driving to the Ring from Dublin and then 3 hard days lapping at the ring'..... I change the oil 3-4 times per year in engine and gearbox, OE airfilters and fuel filters.. Recently had the timing chain tensioners changed as a precaution. Mite have chain done soon.. Yes but GT3 is 993 based motor unlike the 996

Brilliant post. I wonder how durable the new Direct Injection engine will be ? 'Makes the "high" mileage Turbos at 65k and less than £30k seem great value !!

Baz, thanks for the informative and thought-provoking read. I know from reading your buyers' guide that you don't do much work on the 928, but do you have any general thoughts on the 928 engine, as I have read in various places that the engines are absolutely bulletproof and can go for enormous mileages without requiring the endless rebuilds that aircooled 911 engines seem to need. My own experience has been with three examples, a 4.5, a 4.7 and a 32v 5.0 S4, all with mileages well over 100k and none of them consuming oil or behaving other than as they left the factory. All though had regular fluid changes and t-belt / waterpump maintenance. Cheers Joel

Just a few follow ups. Unfortunately I am not privy to what goes on inside the Porsche design department - so it is difficult to state what things may still be weak in the newer engines until they start to fail and come in for rebuild (as the first 996's and Boxsters seemed OK initially). It is only then or by picking up reports of failures on the Internet that I can start to analyse the problem and find explanations and hopefully solutions. However - at this stage - I don't expect much difference from the 997 although Porsche may have improved the composition of the Lokasil preform (to make it stronger or more stable), and the improved IMS bearing may last longer. The newer RMS is different and allows for some of the missalignment of the crankshaft and the RMS locating hole - but then (inexplicably) during the re-design they decided to do without a spring to hold the seal lip tight to the crankshaft when I also believe that the oil being thrown at high speed against the crankshaft next to the seal - increases the leak potential and a spring would have helped resist that and I don't know why it has not been included. I am too busy with problems that need solving day to day to worry in advance too much about new ideas and designs. So I don't look into the design of new engines much until they start to come in broken and I have something physical to look at and ponder over. However an intermediate shaft is not in itself a design problem (all the old 911's had one after all) and without it the sprocket diameters should be increased and if they have not been, this in itself could present long term problems. The Intermediate shaft allows for a more gradual speed reduction but if the oil pump is driven from it (as it is on the 911 and 996) it tends to run with low oil pressure just at tickover (as the speed then is a bit low and needs high quality shells and cranks to last) but apart from that it is not usually a problem. Due to the pulsating loads that result from cams operating - it seems that plain bearings (older 911 design and the OK end of the Boxster/996 shaft) are better than ball bearings on the failing end (or at least don't usually fail so badly just fatigue over time). There is IMHO a little too much pressure applied to the timing chains that wears them against the very long slippers - but this is more to do with keeping them in contact with small sprockets (due to the reduction in diamter of the sprockets to reduce engine dimensions) than the materials. When they do break they just pull out a piece of the link as if that particular link was weak - or they last for ever (if all the links are OK as they usually are). As all older engines will have bores going oval (therefore cracking or increasing blow by) and since crankshaft shells are thinner than I would have liked to see them - by the time most chains are getting tired there are other more important things that should be addressed that are more likely to result in an engine failure. This is why I propose that it will become worthwhile (or perhaps I should say that the public/owners will eventually realise that) for the low cost of the cars and the fantastic performance and comfort - an engine rebuild to fix these problems before a failure occurs - at perhaps around 100 to 140K - will (or should) become the norm and an acceptable cost - OR the additional cost of a waranty/Maintenance Plan (to reduce costs if and when a failure occurs) should become part of the equation when considering ownership. This is one reason why our Lifetime Maintenance Plan is such good value particularly for these cars because not only would it only cost the parts cost for fixing a failure - but we are happy to include the other modifications and replacements to re-condition the whole engine (regardless of what actually failed) without charge (except for parts and any additional labour directly incurred), resulting in a fuly reconditioned engine at very low cost with all our preventative additions - that are not available elsewhere. The 928 is a strange animal. It is under stressed and as most are automatic and very powerful - they spend most of their lives running at low revs and modest acceleration and as a result are reliable for a long time. However several things will eventually catch up with them and then they will prove very expensive to renovate/repair. The 4 valve heads run with softer cams than the 944 S2 and at lower average revs so the small camshaft chain, sprockets and cams themselves - lasts longer - but will probably let go one day after huge mileage. The head gaskets are the same as the 944 S2 and will soon start needing replacement through old age rotting them away and then will cost double the 944 cost. Rubber seals and pipes in the inlets system will eventually fail and be expensive to repair. Finally there are enough computers etc in that car to get to the moon and back but eventually they will fail through old age and copper wire or silver/solder joints will deteriorate through corrosion and when that happens it will prove almost impossible to justify the repair costs. They have been good cars up until now (if you like the sheer weight to drive and dated interior) but I expect them to start being too expensive to own soon for most people (but may last longer before that expensive times starts in drier climates than ours). Finally can I reinforce my opinion that the 996 desrves less criticism and more serious acceptance right now - as it represents by far the best value for money buy of any Porsche I have previously been involved with. Manual or tiptronic are superb to drive, relatively inexpensive to run, extremely reliable and IF (don't forget this next bit when those that prefer something else start dissagreeing) - IF you can afford some kind of protection against the full cost of a very rare engine failure - are low risk buys. You know they are getting so cheap - even if you take the risk of an engine failure (i.e. no cover) compared to what you might have expected to pay a few years ago for anything remotely comparable - they still can be viable. Perhaps the only people who should think hard before buying one are those that spend all their money buying it and cannot afford any extra to cover a costly failure if it occurs - but then this is advice we give to ALL Porsche buyers anyway! (but as a result of human nature is usually ignored) Baz

Ballcock said: noumenon said: Ballcock said: madala said: ....Baz....that was one helluva interesting read.....thanks....if I lived "oop" North I certainly would be using Hartech to look after my 993. Happy Christmas. Try livin in Dublin Is it still full of kids on horses randomly darting out of side streets? It was last time I drove through it! So it was you that ran over me young ones harse lol. Aye, now don't be doin' anyting haaaasty. One of the most frigtening drives ever. Much scarier than my first lap of the ring or first lap of the arc de triomphe.

hartech said: You know they are getting so cheap - even if you take the risk of an engine failure (i.e. no cover) compared to what you might have expected to pay a few years ago for anything remotely comparable - they still can be viable. Baz Actually, that is a really good point... You can buy a 996 AND a brand spanking new engine for the same price as a similar mileage 993 in some cases: and have a newer, faster car, with a more modern interior, etc...

KVA - thanks for that - at last some pragmatic logic recognising the value of these cars on the market at the moment. Baz

Have to make a decision what to do with my 996 next month (balloon finance payment due)... I figured it will cost me more to change into a 997 (which I'm not too sure about tbh) than keep mine and buy a new engine if needed. So I will probably refinance the balloon and keep the car and just be prepared to splash out on a new / recon motor if it all goes tits up at some stage! I'll keep you posted on how high mileage you can get out of a 3.4 original engine... 107k so far and counting

Mine has done 96,000 miles now but had a brand new engine fitted in 2005 by Porsche Reading so has only done 42,000 on new engine and is as sweet as a nut. Does anyone know if they changed anything , would a 2005 engine be identical to a 2000 engine or would there have been a few minor changes ? Edited by woogie on Tuesday 23 December 10:39

kVA said: I figured it will cost me more to change into a 997 (which I'm not too sure about tbh) than keep mine and buy a new engine if needed. So I will... and keep the car and just be prepared to splash out on a new / recon motor if it all goes tits up at some stage! Exactly the thought process I went through earlier this year. The cost to upgrade to a newer car was the same as I might end up spending on a engine rebuild, just to buy into what is essentially the same car (95% of the time). The new warranty costs and restrictions sealed the decision. Thanks for the valuable input Baz, whilst I'm no engineer so cannot comment on your findings, it's all interesting stuff and certainly sounds more than plausable, allowing us 996 owners to make more informed decisions on what to do with these supposedly burdonsome beasts. Chris (71k and counting)

kVA said: You can buy a 996 AND a brand spanking new engine for the same price as a similar mileage 993 in some cases: and have a newer, faster car, with a more modern interior, etc... But... you won't get the additional cost of the new engine back come resale time, whereas the additional value of the 993 will still be there. Not that I'm advocating 993 ownership, just commenting.

Andrew D said: kVA said: You can buy a 996 AND a brand spanking new engine for the same price as a similar mileage 993 in some cases: and have a newer, faster car, with a more modern interior, etc... But... you won't get the additional cost of the new engine back come resale time, whereas the additional value of the 993 will still be there. Not that I'm advocating 993 ownership, just commenting. Have to disagree with you there... I do around 18,000 miles per annum: A 993 with 150,000 miles on the clock (original engine) in 3 years time is not going to be worth much more than my 996 with 30,000 miles on a new engine. The 993 would be needing an engine rebuild and probably much more by then as well, thereby negating the difference.

I agree - for as good as the 993 undoubtedly is - and despite the demand and high prices - many of them are never the less on course for some quite expensive engine and bodywork costs in the near future. Most 996's (on the other hand) have quite a few more years left in them before reaching that age and much of the auxiliary electrical components (and body work parts) seem better to me and less expensive to fix anyway. Although the 993 has legendary low depreciation - even so - as some new models age and also become desireable (thinking of Gt's etc) there is more choice and eventually even rare cars seem to lose value as they fit in with the general ranking including the newer models (my own 924 Carerra GT od which there are probably only 20 or so RHD left in the world and with legendary performance and unique technology (amongst the first with digital ignition I think - plastic wings, flush fitting windscreen etc) is not worth so much as I once expected any more). Because of all this and that 996 prices are so low right now (IMHO) I think they are well worth considering as a better option. Baz

I agree that the current state of comparative values is unlikely to last, and that if you do high enough mileage the cost of a replacement engine will become less significant in comparison to ongoing maintenance . There are obviously situations in which such a plan could work out, for instance if you budget for a new 996 motor but don't end up needing one (jackpot!). However, I doubt that such a plan would prove cost-neutral for typical examples (i.e. 50k miles) and typical mileages. That's not to say it's not worth doing, just that it's unlikely to be free.

hartech said: The 928 is a strange animal. It is under stressed and as most are automatic and very powerful - they spend most of their lives running at low revs and modest acceleration and as a result are reliable for a long time. However several things will eventually catch up with them and then they will prove very expensive to renovate/repair. The 4 valve heads run with softer cams than the 944 S2 and at lower average revs so the small camshaft chain, sprockets and cams themselves - lasts longer - but will probably let go one day after huge mileage. The head gaskets are the same as the 944 S2 and will soon start needing replacement through old age rotting them away and then will cost double the 944 cost. Rubber seals and pipes in the inlets system will eventually fail and be expensive to repair. Finally there are enough computers etc in that car to get to the moon and back but eventually they will fail through old age and copper wire or silver/solder joints will deteriorate through corrosion and when that happens it will prove almost impossible to justify the repair costs. They have been good cars up until now (if you like the sheer weight to drive and dated interior) but I expect them to start being too expensive to own soon for most people (but may last longer before that expensive times starts in drier climates than ours). Hi Baz, I think they got to that point some time ago, hence the high number of poorly maintained examples around, and the "junk" status of the older models. Funnily enough they go for much more money on the continent, if you look on mobile.de a good 928 (original 4.5 version) will set you back euro 10k. Incidentally roughly half of the first 928s were manuals, the trend towards automatics came in the later models. The thing I like about my 1979 car vs my 5 litre 32v S4 is the simplicity: mechanical fuel injection, no ABS etc etc. Whereas you are right, the later models have electronic traction control, electric seats with memory, ECU, EZK blah blah blah. One of the nice things about the 928 is that a number of specialist providers have sprung up to meet the demand for things like replacement MAFs and ECUs. These are parts that are prohibitively expensive from Bosch, let alone Porsche, but by modern standards are not that complex and can be fabricated and in many cases improved upon by small businesses such as JDS Porsche in the UK. This means that we have a support network that can keep these cars going as the factory intended (or even better). Much like businesses like Hartech are doing with the 996. You are quite right that these electrical connections are the real bugbear with the 928. As for the dated interior, it is very different to any 911 but anyone who has enjoyed the driving position and cabin of a 944 will feel right at home. I love the way the instrument pod moves up and down with the steering wheel, the instruments themselves are as good as any Porsche of the era (ie. superb) and little touches like the rheostat controlled variable wiper delay that can be activated without taking your hands off the wheel just make it a great car in ergonomic terms. Add to that full climate controlled aircon and it's not a bad package for 1978. Anyway I've rambled on enough, thanks for the insights and I look forward to the 928 lifetime maintenance plan being offered soon. Joel 79 928 manual - stolen, not yet recovered :-( 87 S4 manual PS: dated != bad

I was trying to be kind Joel - and not controvetial - but not only are most of the ones we used to see in a poor state, but owners weemed to expect miracles from us in fixing them for next to nothing - but also never had all the problems sorted out - so they were always in difficulties. We soon realised that they were not going to fit into the usual remit that enabled our good services to keep other models very reliable for little expense and since two other local independents seemed keen to work on them we decided to drop 928's from our portfolio (as there is plenty of work to go around and we believe in specialisation) and let them get the business and benefit from the experiences - so no chance of a Maintenance Plan from us now (sorry)! We were persuaded by an existing customer with other Porsches that we did look after - to also look after his 928 S4 and reluctantly agreed - but you know it only confirmed what we already suspected - as it got worse and cost more and more with head gaskets, radiator, pipes and connections etc failing and it was expensive to work on. I think it is one for the home mechanic to enjoy. Good luck with yours though - I know there are some very nice examples owned by perfectly nice and sensible people as well - I am sure just like your good self. Baz

sportsandclassic said: No interval on the timing chains...we have started changing them as a preventative measure by fitting split link chains Mike Mike, For 996TT what are your thoughts on split link chains v an endless? cheers Neil

[/quote] Hmmmmm, Pasha interior,looks great even 30 years on.....

hartech said: I was trying to be kind Joel - and not controvetial I think it is one for the home mechanic to enjoy. Baz I don't think any of the 944 range now are good buys unless someone is willing to do a lot of work themselves. My recent purchase 968 for example has already had about 6 hrs from me to fix various electrical and heating niggles and I reckon I have a fair few weekends left to do various other jobs such as fitting new front wishbone castor mounts, drop exhaust to permanently fix broken heat shield and refit side skirts and rear PU, cure slight leak in PAS hoses into reservoir (its a subzero weep PITA type leak that mostly never leaks). It has already had 500 notes spent by me in the garage when I didn't have the time to wait. A car like this would be completely uneconomical to own if one was to get a garage to fix every little problem and get it 100%. I suppose this is the crux of the matter because I get the impression that many can't be bothered, don't know any better or don't want to spend the money to get an old car 100% so just put up with all the faults. Big bills for mechanical stuff I can cope with to some extent, you get a feeling like you are getting a renewed car. Rust however is just to depressing for me, I think the fact that a 996 or boxster is unlikely to have bad rust problems is very attractive.

a) How much is a new 996 engine nowadays? b) How much is the cost to recondition one?

amir_j said: a) How much is a new 996 engine nowadays? b) How much is the cost to recondition one?

TISPKJ said: Dave 321 said: my MK1 Gt3 has 88k miles, put out 361 bhp on a german Maha dyno in May! Doesnt use water, needs a pint of oil after driving to the Ring from Dublin and then 3 hard days lapping at the ring'..... I change the oil 3-4 times per year in engine and gearbox, OE airfilters and fuel filters.. Recently had the timing chain tensioners changed as a precaution. Mite have chain done soon.. Yes but GT3 is 993 based motor unlike the 996 So at what miles do GT3's need a rebuild ? I have not heard of a GT3 needed a rebuild !

My 00 996 has nearly 130,000 on the clock and is still going strong, shame about the few scratches to the paintwork though and my wheels need reconditioning, but it still runs like a dream. Importantly I do not do more than 3-3.5 thousand RPM until the engine is well up to temp. I am not just talking about the water temp. but also making sure the oil is up to temp. which for short journeys means that I am just toodling. But it gets a proper drive at least once a week.

carpmaster said: amir_j said: a) How much is a new 996 engine nowadays? b) How much is the cost to recondition one?

50000 miles on an eight year old 3.4 and all is well. There's a very slight weep from the RMS but it hasn't got any worse in the past 25000 miles so it will get changed when the clutch needs doing. If the worst happens, I've saved enough over the past few years of ownership by using a top-notch specialist and not buying the OPC warranty to pay for a new engine. May swap it for a GT3 next year though....

130K is excellent and shows that the engines are basically sound and reflects the benefits of propper warming up before using the engine to its full potential. However - without wishing to repeat my previous posting - our measurements indicate that the distortion of the bores will be an on-going problem that will eventually become too much for most engines. If it can be rectified soon enough the bores and pistons can be OK but left too long and more expensive work may be needed. Of course the harder they are driven the higher the loads and temperatures and piston blow by - so less aggressive driving may help extend life - its difficult for us to add this into our interpretation of the causes on an old car with several owners we never met. Ironically tiptronics seem to be worse for bore ovality and premature cracking (which puzzled me for a bit) until I realised that the torque converter that allows the revs to rise a bit during acceleration results in me (not neccessarily others) more often than not accelerating from lower revs in gears than I would if it was a manual transmission - which gives rise to higher torque loadings and piston to cylinder wall pressure. Crankshafts can fail a shell main bearing - usually on the flywheel end (we suspect because the additional overhang promotes flexing at that end due to the weight and load on the flywheel/torque converter) - or a big end in a random position (probably because the clearance has become too great to sustain oil pressure within the shell to crank clearance) - although when one goes the reduction in oil pressure to the crankshaft in general often then fails other shells. Similarly with crankshafts - the case hardness is not very deep and the shells don't fit too perfectly giving rise to local wear areas. Once one wears through the case hardness (typically 0.025mm) it doesn't last long afterwards but rebuilding with new shells in time can save the need for more expense. The undersized shells we are testing seem much better made and to have better quality surface finish and materials - so I think the quality of the standard items is not the best available - but time will tell. So although we don't yet know exactly what mileage advice to give about when to rebuild these engines (and anyway even when we do we have to advise on the safe side and there will always be exceptions) - I still think that if one has achieved 100K or so - it may eventually prove to be the best time to rebuild the engine rather than admittedly being often able to get another 20 or 30k or so out of it but then perhaps having to replace many more expensive parts. I appreciate that this could be interpretted as me trying to drum up business and you must reach your own conclusions about that and make your own mind up about my motives. Those that know me personally (and how busy we are and that I am personally seeking to wind down rather than have even more to do) will know that I am trying to offer my initial advice in good faith as a result of measuring and rebuilding lots and lots of these engines over the last few years. Because of my advice that the engines are (for want of a better description) a little more fragile than previous designs and to warm them up well before driving fast - I am pleased to read reports of those that do are getting good mileages out of them - however I suspect that someone with such mechanical sympathy never over revs or over stresses their engines anyway (which really confirms my position). It seems that driven hard, fast and without any concerns from cold - may reduce their life expectancy on average - something older models rarely suffered from but this newer generation will. I still think they are great cars and a bargaim at present. Finally in response to some criticism of me spending a lot of time posting here (and my "winding down" intentions) - may I explain that one of the biggest problems for a small specialist business comes when the founder is approaching retirement age - is becoming less capable than before and finding that the staff around him did not develop sufficiently to be good replacements. This is something we will not suffer because in contrast we have not only have a young director and shareholder (Grant) who is the MD and has been on board from the outset - but we have been following a specific policy to train staff to very high standards - gradualy improving their independence - so that no one is irreplaceable - for many years. We have for example made our own - in house - manuals with full colour pictures showing exactly how to do all the major engine and gearbox work and showing all the special tools and preceedures and torque settings etc. More recently this has enabled me to stand back a little and observe rather than lead (as you cannot train effectively if you are actually still there making decisions and doing the job yourself) and although the lads don't really need to manuals anyway now - it demonstrates a desire to be as good as we can jointly be as a team rather than as individuals and enables us to recruit and re-train to the highest standards. One of the most difficult areas for training is to avoid always being the one yourself to make all the decisions. Typically even when you have left someone with a manual to do a specific job - if they hit a snag they usually prefer someone else to make the decisions. We cannot afford that if we are to exist for many years and move on as people get older or retire - so we try very hard to encourage and train them into a way of making decisions themselves. However I am still sometimes needed whenever something new crops up - more often than not just to confirm that the decision they would have made anyway - if left on their own - was right. Indeed to some extent the development of people demands that they get used to that decision makiing process and good at it. It never ceases to amaze me how capable people can become if they are nurtured by this type of training - as they eventually get just as good (if not better) than you yourself were to start with! As a result we have noticed more recently a huge improvement in the decision making ability and general contribution of our staff - making the need for me to deal with day to day issues - less and less important. This is turn has enabled me to address such problems as these engines in more detail and with more time to concentrate (without distractions) than would otherwise have been the case. Of course I don't actually intend ever to fully retire - but this process is essential for the interest and prospects of the staff as well as the business in general. This staff development is good for our business and great for our customers but does give me time on my hands here at work when I am standing back and observing (or keeping an eye on others who are developing) rather than doing some of the work myself and during those spells I often look at and comment on various postings - offering my experiences and knowlege (for what it is worth) to a wider audience. So please don't think I have nothing better to do - nor that I have such a big ego that I like to be commenting on everything - it just happens to fit nicely into a training situation that now and again gives me a while to sit and ponder whats on the Internet and only in postings where I feel I may have something useful to add - do I comment further. Baz

Yet again - an informative and balanced reply. To confirm my understanding? If a well treated 996 engine reaches 100K and is in sound running order (minimal oil consumption, good compression, good oil pressure no metallic rattles), this would be an ideal time for a rebuild. If this is the case - assuming the condition above, what would be the likely cost of this rebuild (ball park). And crystal ball gazing, how many miles will a cared for rebuild last?

I too would be interested in costings as although mine has done 130,000 miles and uses about a litre of oil a year, in other words it gets done at service intervals rather than need topping in between. I would rather pay out for preventative measures than suffer an expensive and probably cost-ineffective rebuild if it did all go wrong. Plus I get a holiday 'oop north out of it as I would come up and stay nearby whilst the tinkering went on.

For customers not on our Lifetime Maintenance Plan - there are so many options during a rebuild that perhaps the best way to look at it is to state for a car arriving in one piece and running to a car finished - running and road tested - a full strip and rebuild of the engine - replacing all the gaskets and seals (but doing nothing else) etc is presently around £2870 for a Boxster and £2970 for a 996 (+£170 if Tiptronic). Then you can add the following options. To upgrade and replace the intermediate shaft and spindle - £150. To replace all the chains, usual chain guides and crankshaft shells - £329 (+ £40 if hivo chain). To re-round and support all the oval bores £483. To decoke heads and regrind in valves £330. So the total to do all that would be £4262 + Vat (for a 996). There can be other extras like replacing the oil separator, sometimes some exhaust clamps and usually to re-drill and helicoil some exhaust studs that can add £200-£300 to the average bill making the total £4463 to £4562. Then sometimes people take advantage of the situation to fit a new clutch plate etc (if the old one is on its last legs). I suppose this means that around £4500 + Vat should do the job for most people. I can see no reason after a rebuild why the engine should not be good for as many miles as it has already done - but that is not making a promise because obviously none of us know yet what will happen in years to come until it does. In any case it would take many more years to reach that total as cars over 10 years old in general do not on average cover as many miles as in their earlier years, because they tend to become second or third cars by then. Of course costs are much less if the customer is on our scheme and the engine is run until it fails (unless it is a really major blow up) in which case it might just end up similar if many parts need replacing. I hope this helps, Baz

With a '99 996 mileage close to 100,00 and an IMS bearing/crankshaft rebuild 20,000 miles back (whilst under warranty), should I be thinking about preventative work in the near future?

Rossfitz - probably not - it is just such a shame that the ovality that will have been present in the cylinder bores was not done at the same time - but now only worth waiting to see how long it lasts as you have little to lose by waiting now that the other jobs have been done. Baz

Baz - Thanks for that. Will there be any signs/symptoms of ovality about to cause problems? Thanks Ross

Not really - it's a difficult subject to cover here as there is a gradual loss of bottom end power/torque. It is not really noticeable during ownership because it is so gradual a loss that you don't notice it creeping up over the years - or in your period of ownership. To explain why - the power/torque an engine develops is due to the compression pressure before ignition - i.e. mixed fuel does not produce the same burn pressure to push the piston down when it is at different pressures before ignition. This is why the old easy tune up solution was "high compression pistons" - the same amount of fuel and air was trapped but it was compressed to a higher pressure before ignition. Everything people do to tune an engine tries to squeeze/suck more air into it so that when it is compressed it reaches a higher pressure before ignition. This is indeed what turbo's and super chargers do. So long as the compression is not so high that it causes the fuel to explode rather than burn - the higher the pressure the more power (from the same volume of air/fuel) you get (this is also why turbo charged engines have lower geometric compression to compensate for the extra air being blown in that would otherwise lead to an exploding mixture - detonation). All the variable cam lift and timing sytems do is to make the engine breath better at different revs - without harming the breathing at peak revs - which in turn feeds mor air into it and results in a higher compression pressure before ignition at lower revs. This is particularly important at low revs because it is easy to manufacture an engine have the perfect compression ratio when it is running at its most efficient breathing (somehwere near peak revs) but after that all the breathing at lower revs traps less air and reaches a lower compression pressure before ignition. (In fact this is why two strokes suddenly produce a huge turbo like power increase - not as often stated because the exhaust system suddenly resonates but because it finally traps enough air to produce a "powerful" burn). It is quite true that if an engine had a variable compression ratio - this would enable better torque and power at lower revs but as this has not been done yet - better torque comes from better compression pressure. Now as the bores go oval (as the pistons are already made oval anyway) the piston clearance increases a lot and the rings do not seal as well in the oval bore so the precious amount of trapped air at low revs leaks down the bore and lowers the compression pressure before ignition. In leaking down the bore it pushes the oil film down and overheats the oil, the face of the bore and the pistons and this is why most older 996 engines that seize - unusually - do so on just one face. You only notice this gradual loss of torque after having the engine rebuilt after correcting the roundness - as a noticeable increase in sharpness and bottom end torque and acceleration. As long as high mileage engines are not driven excessively fast with less than full throttle in high gears - they may run OK until the bore eventually cracks (which might be a long way off). But if they are driven with the same gusto as when they were new - they may well fail prematurely. The actual bore (and ring) wear is not high because the extra clearance comes about by the round bore getting bigger in one direction and smaller in the other so when they are re-rounded - the wear is relatively little. Since the cars are capable of in excess of 160mph, any normal sensible driver wanting to preserve their high mileage engine can still obtain excellent performance without over straining it - so usually as cars age and are worth less the owners also tend to on average drive them less agressivley than some who can afford a new Porsche and for all the money they paid quite rightly expect to be able to thrash the bo***cks of it without it comming to any harm. When is the best time to fix this problem is difficult to asses due to the different driving styles influencing the rate of ovality (and who knows how a previous owner treated the car) - and as several engines have failed with cracked bores at 40K to 60K + but some others at 130K are still Ok - it is difficult to set a figure. However taking on board all the other failures (that a rebuild can refresh/avoid like chains, IMS bearing, crankshaft shells etc) and relevant ages (for seal wear etc) and mileages - it just seems to me that anyone wanting to keep a car for a lot longer - with around 100K on the clock - would benefit from a rebuild around then before failures increase the repair costs. Or they could get on a waranty scheme and not worry about the extra repair costs and simply await the outcome. If a clutch was needed soon and exhaust system bolts and joints were corroding etc it might make more sense to address all the problems in one go - as buyers of older Porsches expect to do and frequently authorise. In all this - reducing the strain on the engine as it ages will usually produce benefits for longevity. I hope this explains it better. Baz

Couldn't be clearer. Thanks for taking the time to explain the implications. Looks like clutch replacement time is worth a trip up North.

Fantastic info Baz , it's really great that you take the time to post in such detail , we would not have access to this type of knowledge if you chose not to share it. Ignore the knockers ,nay-sayers and begrudgers and keep it coming!

Ballcock said: Fantastic info Baz , it's really great that you take the time to post in such detail , we would not have access to this type of knowledge if you chose not to share it. +1 I always take the time to read the hartech posts, I've not seen these things explained in such a detailed and easy to understand way anywhere else. I'm sure you could put a book together from all the posts you've made on PH - I'd buy it

hartech said: Some stuff.... All of a sudden you realise what a good thing Barrel base gaskets / through bolt seals leaking is. It acts as a catalyst for you to go in there and freshen the engine up !! It`s the same problem with a lot of the 3.2 Carreras. They don`t leak, keep running but breath like a steam train and really need the engine opening up. He

996GT2 said: Ballcock said: Fantastic info Baz , it's really great that you take the time to post in such detail , we would not have access to this type of knowledge if you chose not to share it. +1 I always take the time to read the hartech posts, I've not seen these things explained in such a detailed and easy to understand way anywhere else. I'm sure you could put a book together from all the posts you've made on PH - I'd buy it +1 more

amir_j said: 996GT2 said: Ballcock said: Fantastic info Baz , it's really great that you take the time to post in such detail , we would not have access to this type of knowledge if you chose not to share it. +1 I always take the time to read the hartech posts, I've not seen these things explained in such a detailed and easy to understand way anywhere else. I'm sure you could put a book together from all the posts you've made on PH - I'd buy it +1 more -1 I wouldn't buy it as it's all right here for free on PH!! ( ) What it has done, however, has instilled in me a lot of confidence in the Hartech outfit, and when I'm ready to buy some pork (shortly, hopefully), Hartech is probably the first place I'll look.

Yes Henry - as you know well - the 3.2 wears rings at an alarming rate and with similar loss of bottom end breathing and lower compression pressures resulting. Eventually because this loss of bottom end breathing changes the air flow meter mixture ratios and people start to fiddle with the air flow meter settings or put up with very rich mixtures. When badly worn they drive more like a 2 stroke - only achieveing good compression pressures and performance when the cams make the engine breath well anyway - 3500 to 4K revs. The difference in bottom end that results from a rebuild is amazing. People seem to accept the benefits from having a 3.2 top end rebuild, a 964 top and bottom end, a 944 head gasket or pinion bearing, 944 S, S2 and 968 cams and pinion bearings - yet for some reason - to refresh a 996 (a much more powerful car) at over 100K for similar costs is heavily criticised. Bearing in mind that during the rebuild several potential critical failures can be modified to prevent them occuring again - I find it odd that the cost is so criticised. Indeed if at 100K a car (that has then reached low or minimal depreciation) got a rebuild at say £3-4K - that would then last it until say 180K (the end perhaps of its life anyway) that works out at about 2p/mile. For anyone on our Lifetime Maintenance Plan the costs of fixing a fault are so low that it seems like a no brainer (as they say) to me! When I go into our local crankshaft regrinding/reboring centre there are always lots of powerful engines being rebuilt, XR2 turbos, various Japanese engines at lower mileages - I don't know if their web sites contain similar uproar - I somehow doubt it. I guess it is just the expectation of longevity from the period when Porsche were going bust - that has been knocked the reality of life with a modern bottom of the market Porsche in the present World? Baz

hartech said: It is quite true that if an engine had a variable compression ratio - this would enable better torque and power at lower revs but as this has not been done yet - better torque comes from better compression pressure. Believe it was SAAB had a go with an engine that had a cylinder block that could rotate about the crankcase. It would be sat on top normally giving a higher compression ration but when full beans were summoned, the cylinders were rotated (crank pin and cylinder block arc didnt share a common point) effectively moving the head further away from the crank and reducing the geometric compression so more boost could be thrown in without detontation. Very hazy memory of this, it cropped up in a random lecture at uni ~5yrs ago. Dont think the engine ever got close to production though.

I didn't know about the Saab engine emicen but I must say that in my view a variable compression ratio engine is the way to go in the future! When I left the motorcycle industry I had worked out that this was the way to go for a two stroke and indeed had 2 ways worked out of doing it - but - both needed extensive digital electronic controls that were simply not available then and masses of dyno work to perfect - which I knew no British Business had the stomach for. Baz

hartech said: 1 It is quite true that if an engine had a variable compression ratio - this would enable better torque and power at lower revs but as this has not been done yet - better torque comes from better compression pressure. 2 As long as high mileage engines are not driven excessively fast with less than full throttle in high gears - they may run OK until the bore eventually cracks (which might be a long way off). But if they are driven with the same gusto as when they were new - they may well fail prematurely. Baz Hi Baz, I sincerely appreciate you taking the time to tell us this much about the Porsche engines, Thank you very much. I have two questions about your post that intrigues me. 1 re: compression ratio. How does this work? When I read about the compression ratio of a normally aspirated Porsche engine, it the bar number the times the air is compressed or the actual force the piston is subjected to when the fuel burns? I'm confused on this. 2. Why does it matter how much throttle you apply on a worn engine in relation to the speed you are driving? Does this mean that it's better to go full throttle/no throttle as on a race-track? Can't you cruise with a worn engine at 120mph? Why is this? Thank you very much.

Decanter said: Hi all Reading this thread with interest regarding higher mileage 996's, and some superb posting from Hartech; very informative and very easy to understand for a numpty such as myself. But regarding the 996 longevity I have a question................. most is without doubt answered regarding the engine but I'm also wondering about the gearbox on these cars, I remember some information in the past that these weren't able to be reconditioned, and that it was necessary to purchase an exchange gearbox from Porsche at substantial cost, else a used item, is this still the case? Or are spare parts now available for the rebuild of these gearboxes? Sorry if this is a daft question, but for someone like myself it could make all the difference to a potential purchase knowing details such as this. To save Baz a load of typing, have a look at what he wrote in this thread a few moonths ago. http://pistonheads.co.uk/gassing/topic.asp?h=0&amp...

The compression ratio is worked out as follows. You put the piston at top dead centre and fill the engine with fluid from a burette to measure the volume inside the engine on top of the piston at top dead centre (you do this through the plug hole with the cylinder vertical making allowance for how far up the spark plug thread you go to allow for the volume inside the spark plug). This is called the clearance volume. The area of the bore multiplied by the stroke then gives what is called the swept volume. The compression ratio is the swept volume plus the clearance volume divided by the clearance volume. So if a cylinder is 100ccs and the clearance volume is 10ccs the compression ratio is 11 to 1. As you can see this is relatively meaningless as it only tells you a story about the physical construction of the engine. The compression pressure that results depends upon how much air is trapped in the cylinder when all the valves are shut before it is compressed. At low revs relatively little air is trapped so the result of compressing it 11 times is still quite a low pressure. When an engine is breathing at its best it will be close to sucking in its own volume in air and the compression pressure may well be 11 times more than it was at atmospheric pressure (and there are a few complications for temperature etc as Boyles law relates pressure and temperature etc - but these do not change the basic theory). One of the engine dynamic - heat engine thermodynamic laws reflects this relationship between power and compression ration but expressing it as a figure to the power of the compression ratio (but I cannot remember what it is called - only how it all works) How much air it can trap compared to the swept volume is called the "volumetric efficiency" of the engine. The first engine I am aware of to achieve 100% volumetric efficiency (i.e. to suck in the swept volume entirely) was the NSU rennmax 250 cc 4 stroke twin of the late 50's era. Everything that can be done to a normally aspirated engine (one that sucks its own air in) to increase the amount of air it can trap at high revs - unfortunately reduces the amount it can trap at low revs and visa versa. So tuning has always been a compromise to achieve the best all round entrapment for the application - lots of power at high revs for racing or lots of power/torque at low revs for heavy pulling etc. Varying the timing of various features effectively makes the engine like different engines would be if they were not variable - so you can improve the breathing at a wider range of revs. So altering the valve timing and/or the valve lift, changing the induction length etc can broaden the power band. Pumping air in under pressure can exceed 100% volumetric efficiency and hence be more powerful than a normally aspirated engine and therefore can increase pressures so much that the fuel explodes and that is no good for producing power. For any situation the more you open the throttle the more air is trapped in the engine so the higher the pressure before ignition and the higher the burn pressure of the fuel. The piston is pushed down by that pressure (like your leg pushing down on a bicycle pedal). The higher the pressure the greater the push. The crankshaft is rotated by the piston pushing hard against the cylinder wall and transferring that downward linear pressure into rotation through the connecting rod that connects the piston to the crankshaft (again rather like a leg and a bicycle pedal). The more the throttle is opened the more the piston pushes against the cylinder wall and the greater the pressure trying to force burning fuel past the piston and rings and down into the cylinder bore. So you can cruise at 120mph - what is relevant is how quickly you want to reach 120mph. Acceleration is proportional to torque (which at any given revs is proportional to power) - so the faster you want to accelerate the more power or torque you must produce and the greater the resulting forces on the piston wall creating piston blow by. So if say you used three quarters throttle - you would trap less air, have lower compression pressure, lower forces on the piston and cylinder wall and less piston blow by - also less power - but you could still reach 120mph - but more slowly than if you used full throttle (which would strain the engine more by getting there more quickly). The effective weight (or inertia forces) of engine parts when they are accelerating and rotating is magnified by the revs in more or less a cubic ratio. So higher revs results in very much higher mechanical loads from those parts moving about in the engine and hence strains the engine more than a straight ratio increasing linearly with speed. This is why the way you drive the car as it ages influences its lifespan - both in terms of how soon you drive fast when warming it up, how much you open the throttle and how many revs you often use before changing gear. Similarly someone who happens to drive modestly from new will have an engine in better condition and likely to last longer than one that was accelerated at full throttle to peak revs from cold, from new and for all its life. People used to driving lots of the same models can tell the difference in the feel of the car and good dealers will select those that have had a relatively sedate life and may refuse to buy or part exchange a car that has been worn out prematurely as it will only backfire on their reputation and pocket. The main gearbox parts usually needed are available now. The biggest problem seems to be that the main bearings are shrouded with a seal (just like the ill fated IMS bearing) and that this prevents the washing away of minute wear particles, allows the oil to get hotter and does not replenish it quickly - but they can be replaced. The other main problem is that older gearboxes allowed you to move the gear lever and gear as far as it could go until it was fully engaged and this was effectively the gear change stop mechanism. This worked well but you could usually feel the gear jamming into place slightly back though the gear lever when it was fully engaged. These gearboxes have a different stop that prevents the gear lever moving the engagement dogs fully home into gear (so you do not feel it coming to a stop) and this makes the gear change feel sweeter. The last part of the engagement is taken up by spring loaded pawls inside the synchromesh. This would be good if the set up was set perfectly, but two things alter that perfection. (1) The shaft is moved by shims to get the best position and (2) the engaging shafts, bearings and selector forks etc wear. If the original setting was perfectly in the centre (so for example the movement for 1st and 2nd was exactly equal in both directions) then even with wear it would probably work OK. Unfortunately - for some reason the setting seems to favour more movement in one direction and less in the other until with wear the engagement with the least movement doesn't quite move far enough to allow the spring pawls to drag it further into place and the synchromesh sits half in and half out of gear. Then when you let the clutch out - sometimes it slips into gear and sometimes it doesn't and slips out again. Because new parts are less worn, changing to them can improve the gear change but a better solution is to re-set the positioning so that it is central and fully engaged in both 1st and 2nd anyway. I hope this answers your recent questions, Baz

emicen said: hartech said: It is quite true that if an engine had a variable compression ratio - this would enable better torque and power at lower revs but as this has not been done yet - better torque comes from better compression pressure. Believe it was SAAB had a go with an engine that had a cylinder block that could rotate about the crankcase. It would be sat on top normally giving a higher compression ration but when full beans were summoned, the cylinders were rotated (crank pin and cylinder block arc didnt share a common point) effectively moving the head further away from the crank and reducing the geometric compression so more boost could be thrown in without detontation. Very hazy memory of this, it cropped up in a random lecture at uni ~5yrs ago. Dont think the engine ever got close to production though. I recall this from autoexpress (or similar) back then. Google turns up this: http://en.wikipedia.org/wiki/Saab_Variable_Compres... http://www.carenthusiast.co.uk/2000/shows/geneva20... Highlights: The five cylinder in-line, 1.6-litre Saab Variable Compression engine on display generates no less than 225bhp (almost 150bhp per litre!) and yet can return the fuel economy of a conventional 1.6-litre engine with less than half that power. Linked to a powerful supercharger, the Saab Variable Compression (SVC) engine can deliver the power of a 3.0-litre engine while operating at a relatively low 8:1 compression ratio. However, it can also run with a much higher compression ratio, up to 14:1, for good economy at smaller throttle openings when the supercharger is ‘off-boost’.

Baz, you are fantastic! Thank you so much for your brilliant explanation!

+another vote for Baz. Very informative stuff for 996 owners.

Thats really interesting as I didn't realise that anyone had made a variable compression engine. I did it the easy way by running an engine on a dyno with different static compression ratio cylinder heads (swapping them over and doing another test run) - so I could plot on a graph the change in compression ratio (with revs and throttle opening) that gave the best results - and then I worked out 2 ways to achieve this variable compression engine with a 2 stroke engine - one varying the cylinder height hydraulically (but it would need quite a big pump to move quickly enough) and the other rotating an eccentric sleeve around the crankshaft main bearings via a pivoted arm and smaller hydraulic cylinder (both of which also altered the exhaust and transfer port heights - similar in a 4 stroke to changing valve lift and timing - so providing a double whammy of variable compression and valve timing). It was interesting (even remarkable) to see the results in which a dyno run at low revs with relativley little air trapped and therefore low true compression presure that normally gave small power output - would transform into a very powerful delivery (despite the small amount of fuel) once the compression pressure was raised sufficiently to achieve suitable temperatures and pressures before ignition. I have been trying to remember the formula for efficiency of an OTTO cycle engine (4 stroke gas burning engine - in this case the gas being petrol and air). I think it uses rules for the adiabatic cycle (on the grounds that there is insufficient time for the gas to draw much heat out of the surounding cylinder walls and head) and that the formula for efficiency is 1-(1/r) (where r is the compression ratio) the result in brackets being raised to the power of constant for the gas used (say X) -1. In other words the higher the compression ratio the smaller the figure in the brackets and therefore when you take that from 1 the larger the answer (or efficiency). (Sorry if thats wrong it was over 40 years ago)! This is largely due to Boyles law which I think is that as the volume reduces under compression the pressure rises proportionally. So the higher the compression ratio the higher the pressure of the gas before ignition and the greater burn efficiency and burn pressure results. The work done raising the pressure is seen as an increase in the temperature of the gas - so higher compression results in greater efficiency and higher temperatures (and a better - more powerful burn). Pre-ignition occurs when the pressure rises so much that the gas reaches its ignition point/temperature before ignition by spark and therefore beats the ignition timing. So much for the theory (possibly flawed by senility) but the fact remains that compression pressure is the key to performance and worn or oval bores, rings, head seals or valves - all throw away the potential performance otherwise attainable - particularly outside of the natural hot cam timing points. Baz

Actually, Saab made a variable compression engine about 6 years ago, though I do not know if it made it into production. Essentially it relied on the speed of the crank to determine in internal device..... that lifted the head by about 2-3 degrees.think about it pivoting on one side.belows included...but no drawings do I have.... i remember reading about this in my local Audi dealer at the time,[mag escapes me] and thinking wow, how simple, yet revolutionary....anyways it has been done and Saab where there, Kevin

Would you guys allow me to indulge in a little mild bragging about my past and in the process go off subject a bit and tell a few tales of interest to those who enjoy engine tuning subjects and information? My variable compression work was done in 1976 (just a few years before Saab) but I never managed to complete it due to lack of support and electronic ability to make the control system. Howver once I knew (and had proved in a fixed state) it worked - the incentive to prove it was less than the satisfaction of having found out something that at the time I had never known anyone else discover. That is not to say something similar hadn't been done before - in fact I saw a photo of a 2 stroke engine made in the 30's (I think) with a variable cylinder height (using a rotating cylinder rising and falling up and down on a thread) - but the pictures I saw never linked the reason for building it to compression ratio - but instead to port timing. I fully expect that the engineer knew all of that then and there is often nothing new in this World and usually someone else - you find - already did most things before. I did however make a variable exhaust port for the armstrong two stroke engine using a flap valve - that worked. It basically restricted the exhaust flow at low revs by holding back the flow - this effectively delayed the timing at lower revs and improved entrapment so raising compression ratio (and I still have such a cylinder still at Hartech). Apparently 2 years after leaving Armstrong Motorcycles - they were Involved with Honda to use a new 125cc two stroke engine with an apparently revolutionary exhaust flap valve they proudly showed off the the directors - one of whom slipped out to the then unused dyno room and from inside a dusty cupboard, pulled out my identical system tested several years before and to the utter amazement of the Japanese - blew the dust off it and plonked it on the board room table. It was only when I was watching a dyno run in which lots of air and fuel were visibly going into the engine while it was producing very little power and that there was very little difference to the amount going in when it suddenly took off - that made me suspect that it wasn't the dynamic flow of inlet, exhaust and resonant tuning that determined the power band (as frankly everyone in the World had previously alluded to) but that it was actually possible that there is a true compression ratio (i.e. an actual compression pressure) below which little power results and above which the burning changes into a much more powerful burn. This puts a new theory in place to suggest that the formula for performance is not just that power increases with compression pressure but that there is a minimum pressure under which the burn is under impressive and a slightly higher pressure after which there is a huge jump in performance (something I never previously knew). It proved that actually the compression pressure was far more important than the inlet, exhaust and ignition timing - the inlet or exhaust tuning or the induction length - and they were all the things everyone had spent all their time developing and working on (and it may be that such things are known now and taught but not when I was in the education system). Fitting increasingly higher compression cylinder heads resulted in this engine (that was supposed to be so highly tuned it would not pull the skin off a rice pudding - as they say) at low revs into a very powerful engine at those same low revs and with the same "high rev" tuning. Eventually the very high compression head seized the engine at high revs but not until a graph had been produced to prove the benfits of a variable compression engine (reducing as the revs increase). It showed a huge power band despite being basically highly tuned and previously with a very narrow power band. This in turn meant that an even higher state of engine tune could be used but still produce a big enough power band to start and accelerate through the gearbox. It would undoubtedly have been a "World beater" but then it would have either been copied or banned by the governing body and I probably would not have got the credit anyway. I say this because around that time I received from the motorcycle racing governing body (the FIM) a letter stating that in future the number of cylinders would be determined by the number of combustion chambers! This was extremely odd to say the least! 500cc GP events were limited to 4 cylinders at the time and two strokes were dominant. I don't know which manufacturer was behind the change but Honda wanted to compete with a 4 stroke but needed 8 cylinders to do so which would be illegal. Realising what they were up to I wrote to the FIM and asked if 2 pistons in 2 bores (or 8 pistons in 8 bores with 4 combustion chambers - in pairs) had a common combustion chamber (or 4 common combustion chambers) - would it be a regarded as a single cylinder (or a 4 cylinder) and they replied "yes" - plot exposed. I then asked - if two combustion chanbers were linked together would this be one cylinder - they said "yes". Finally I said - how big would the "link between the cylinders" have to be - would a 0.25mm hole drilled between 2 otherwise seperate combustion chambers turn it into one chamber and the two cylinders into one? Having made it clear that I understood the scam and therefore could also make an 8 cylinder 2 stroke that they would have to rate as a 4 cylinder (and effectively stop Honda from benefitting) - I got no reply - but shortly afterwards the original change previously notified was reversed and we returned to the obvious logical relationship of pistons and bores determining the number of cylinders. A story just to demonstrate how devious big business interestes can be! I also produced a carburettor throttle slide that as it moved - opened the disc valve inlet timing as well (so automatically varied the inlet timing in line with the throttle opening) and a thermocouple fitted to an electronic box that prevented seizures (common in two strokes of the era) by detecting the rise in cylinder temperature in time to switch off the ignition before it seized up. But like many things - at the same time - usually different people around the world come to the same conclusions and all invent something similar and new at the same time. I also patented the pull through suspension unit used on the Carbon Fibre Framed racing Armstrong motorcycle that we developed and that won the British Championship 3 years running - but I don't think this has been used again even though it was superior, lighter and resulted in a lower centre of gravity. When I moved on to run a Carbon Fibre developement factory - I was called to a grubby workshop (the size of a kitchen and crammed with machinery) where one man on his own had - over several years of hard and unrewarded work - developed the first carbon fibre framed bicycle. I advised him to sell the idea to a bigger business or it would be copied anyway and indeed it became the famous frame that won in an olympic event and the origin of which was claimed by a major manufacturer - but I never saw his name mentioned again even though I know it was all his work - poor sod. I think nothing is really new and probably you can always find someone that thought up similar solutions years before but I do know that when I worked out how important the true compression pressure at low revs was - it was not copied or stolen from anyone but the results of my own testing and investigative thought processes and I don't care who believes that or not - I know the truth and that is all that matters to me. It also explained so many other things I had noticed in various engines over the years and for me became one of the most important issues in engine development or repair. I am however suprised that this compression pressure issue has not to my knowledge been raised elsewhere (except it seems with Saab) as it is crucial to performance and extremely relevant to the performace of engines as they age and the wear reduces performance - particulcrly at low revs. p.s. I am also currently in talks with a publisher - so you may actually find a book appear one day with many more similar stories, theories and explanations - as long as I can finish it before I forget it all! Enough of my ego boosting reminiscing and trying to fool myself that I was more important to engine - engineering than I know I am - overalls back on and back to the real world in the workshop where there is a gearbox to rebuild and a special tool to make - damm it - it's much more more fun fooling yourself about what might have been! Baz

On the subject of variable compression engines, Mercedes are currently working on what they call a 'dies-otto' engine. In testing, a 4-cylinder nominal 1800 cc engine of this type was fitted to an S-class and returned about 50 mpg (IIRC) with the same performance as an S-320 CDI (I think it even had slightly more torque and low end acceleration!)

Here's an odd one. I have a 99 996 cab with 87k and full service history.It has always had good oil pressure (3bar at idle and 4.5 at speed) It went in for its MOT and when it came back oil pressure was only 1 bar at idle or speed. Sounds and runs ok at present. Started it from cold this am and idle pressure was 3bar (will reudce when warm) but when the engine was revved it DROPPED to 1bar only to return to 3 bar when idling again. Anybody heard of a 996 suddenly with such low oil pressure or more peculiarly DROPPING when revved.Any Ideas??

brown996 said: Here's an odd one. I have a 99 996 cab with 87k and full service history.It has always had good oil pressure (3bar at idle and 4.5 at speed) It went in for its MOT and when it came back oil pressure was only 1 bar at idle or speed. Sounds and runs ok at present. Started it from cold this am and idle pressure was 3bar (will reudce when warm) but when the engine was revved it DROPPED to 1bar only to return to 3 bar when idling again. Anybody heard of a 996 suddenly with such low oil pressure or more peculiarly DROPPING when revved.Any Ideas?? sounds like you've got a bad oil pressure sensor.

It does seem likely that there is a fault with the sender or guage - but strange that it went wrong while at the MOT station? If in doubt it is always worth checking the oil filter for bronze particles and the oil pressure relief valve (in the oil pump) to make sure it has not stuck possibly with a bit of debris (as it is possible for a small piece of the silicon they stick the crankcase joints together with to come lose and float round to the valve and jam it). I feel sure it will be OK, Baz

Thanks Baz will do.I cant see that the MOT station could have done anything although they did replace both of the rear to front brake pipes and renewed an AC pipe joint just behind the front drivers door. I have let them know about the problem just in case.If this sparks anything else in your mind let me know. Thanks again.

Well, I thought you might like to know how we are getting on with this peculiar problem. It not the sender,the gauge or the oil pressure release valve. All been tested and there is genuinely low oil pressure No debris or metal particles in oil or filter. No water in oil or oil in water. No noises or smoke. Car still has v low oil pressure which DROPS when engine is revved and rises (slightly) at idle. Now checking for faied or failing oil pump.

Pretty much has to be a failed or failing pump then... IMHO. How is the pump secured to its shaft? Is there a woodruff key or alike? It sounds like it could be slipping as rpm is rapidly increased? Or, it could just be worn internally... Will be interesting to hear what the problem is.

brown996 said: Well, I thought you might like to know how we are getting on with this peculiar problem. It not the sender,the gauge or the oil pressure release valve. All been tested and there is genuinely low oil pressure No debris or metal particles in oil or filter. No water in oil or oil in water. No noises or smoke. Car still has v low oil pressure which DROPS when engine is revved and rises (slightly) at idle. Now checking for faied or failing oil pump. I hope you have someone very good on the job.

brown996 said: Well, I thought you might like to know how we are getting on with this peculiar problem. It not the sender,the gauge or the oil pressure release valve. All been tested and there is genuinely low oil pressure No debris or metal particles in oil or filter. No water in oil or oil in water. No noises or smoke. Car still has v low oil pressure which DROPS when engine is revved and rises (slightly) at idle. Now checking for faied or failing oil pump. Well for those interested, the oil pump was removed and checked and is fine. However on draining the oils, the oil filter was removed and was found to be crushed up inside the housing.The pump was refitted, with a new filter and oil pressure is back to normal. Feeling is that the oil separator (there is a lot of oil around it but no tell tale smoke)is damaged and somehow created a vacuum that has crushed the filter element. We may never know for sure, but it too is being replaced (manual car) so all seems to be on the mend now...... without a new engine!

brown996 said: brown996 said: Well, I thought you might like to know how we are getting on with this peculiar problem. It not the sender,the gauge or the oil pressure release valve. All been tested and there is genuinely low oil pressure No debris or metal particles in oil or filter. No water in oil or oil in water. No noises or smoke. Car still has v low oil pressure which DROPS when engine is revved and rises (slightly) at idle. Now checking for faied or failing oil pump. Well for those interested, the oil pump was removed and checked and is fine. However on draining the oils, the oil filter was removed and was found to be crushed up inside the housing.The pump was refitted, with a new filter and oil pressure is back to normal. Feeling is that the oil separator (there is a lot of oil around it but no tell tale smoke)is damaged and somehow created a vacuum that has crushed the filter element. We may never know for sure, but it too is being replaced (manual car) so all seems to be on the mend now...... without a new engine! Have you considered having an oil sample analysis done to look for trace elements of bearing material?

So whats the going rate for an IMS upgrade/replacement if you are interested in preventative work?...should the RMS be done at the same time? Can anyone recommend somewhere to have this done?...central South Coast here....

If it’s not gone by now, I’d leave it

jonny996 said: If it s not gone by now, I d leave it IMS can go at any time...I think £2K will sort IMS/RMS

Philip Raby near Bosham is a Porsche Specialist and there's Precision Porsche and 9Excellence.

More chance of causing an issue changing an IMS than it letting go now. I would not touch a car that has had an IMS done now. Most of the replacements people use are only good for 30-40k miles anyway. Most failures were due to poor tolerances, hence why they let go within the first 40k miles or so (99.9% of the time). Fitting a new bearing for one that is good after all these years is madness. Unless you go for a larger solid type bearing then forget it. Have a read of this.... https://911uk.com/porsche/ims-advice-please-and-he...

Yeah, I had mine done when I had the tensioners done beginning of last year and I should have just left alone. Despite having 230k miles in it, the IMS came out with zero play. Was a waste of money. Leave it alone.

Having just acquired a higher mileage 996, I've done a lot of reading of this too and also agree, seems there is little point in doing an IMS that has survived its early life, you will likely create a problem or at least expense where there is not one. There is a pretty significant commercial operation around the world that lives off the IMS story, so plenty of marketing and scaremongering goes along with it. Monitor your oil regularly and just react if you start seeing metal in it which indicates a failure. That's easily the best thing to do.

shiversaint said: Monitor your oil regularly and just react if you start seeing metal in it which indicates a failure. That's easily the best thing to do. Yep, I know someone who sends off his oil once a year to be checked. So far so good. Is that enough, though? If they detect metal flakes in the oil, do you still have time? I understood that when it goes, it's sudden and dramatic.