My 200,000 mile refresh.

Planning on doing an engine out refresh when I hit 200,000 miles in my '98 build 996 C4 This thread for planning purposes, as I still have about 2 oil changes to go before I hit the magic number, and I want to start ordering parts as I see them on sale, and get some advice from the experts here. I have borescoped and see no evidence of scoring or cracking, and I have no other major problems, so it is a preventative rebuild. Please chime in with any ideas you have, or advice. All welcome. My basic idea is to refresh the engine and get to 400,000 miles. So what would you do if you wanted to get another 200k out of the engine? I expect to replace all rubber hoses, mounts, clutch, IMSB, chain tensioners, plugs, plug sleeves, coils, rear main seal, front seal, AOS, etc. etc. I think I have to split the case to get to the main chain tensioner, so if I do, I expect I would put in new main and rod bearings.? Would you do rings? I figure I would pull heads and send them off to be reconditioned and replace springs. Any other advice? I will keep adding info and get a list together. Once I begin the project sometime in late '24 I will update the thread with my progress. Thanks to all for your input. I should note that I have already put in a low temp thermostat and new housing.

Congratulations on making it to 200k! That is an achievement. If you are going as far as splitting the case then do a full rebuild. Your bores are no longer round and new rings will likely no seal. Your valve train is also going to be well worn and benefit from guides, and new seats. The additional cost for new Nickies, pistons, is a small percentage of the total cost once you split the case. Once rebuilt, you will have the best opportunity to go another 200k, but with better parts than factory this time.

That engine will go well beyond 300k. If I were you, I�d leave her closed. Don�t open it up. You already scoped the bores. Leave everything alone internally aside from chain pads and tensioners. you could do cam cover sealant. I would change the AOS. Because it�s a dual row IMSB, I would also leave that alone. spark plug tubes, sure. Coils and plugs can�t hurt. fuel filter and fuel pump. change the oil. I use liqui Molly 5w-40 synthoil prem - toss the MSo2 and lifter additive in there. Only do it once though. Stick with liqui Molly thereafter. seems like the car is in good shape. Don�t mess with it too much. My $.02

Congrats on the miles. Consider replacing oil cooler and power steering lines. I had engine out two years ago and didn't think to replace the power steering lines and ended up springing a leak about 9 months later. Should, would, coulda.

My recommendation would be to stay off the track. My motor would probably still be running at over 200k but repeted 7k rpm at watkins glen did it in.

I expect to replace all rubber hoses, mounts, clutch, IMSB, chain tensioners, plugs, plug sleeves, coils, rear main seal, front seal, AOS, etc. etc. I agree with your plan above, but I don't see the need to go much beyond this now. I'd replace the oil cooler at the time of changing the clutch, IMS bearings and AOS. I've asked my tech if we shouldn't just replace all the hoses and he rolled his eyes. There are 23? different coolant hoses. Had one go on me just hours after coming out of winter storage, which ruined my day, but that one hose seems to be a common failure point. Fortunately mine is a cabriolet and the top is never up, so I knew right away there was a problem when I was engulfed in a cloud of steam at the next stop sign. Congratulations on making it so far. Do you have any thing special in the way you care for your car that you owe this good fortune to? Yeah, badly worded...but you know what I mean.

In my opinion you should either leave the case as-is and see how far you can go, or split the case and do everything. (Including Nickies and The IMS Solution)

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I understand that in order to replace the wear pad on the crank to IMS chain tensioner, that you have to split the case. Can anyone confirm if this is true or not? If I don't have to split the case, I won't. I do plan to pull the heads though, as I can't imagine the valve guides and seals will be ok in another 200k miles.

U can only do the the 2 short chains, variocam pads and long chain pads without splitting the motor. If u split it do it all.

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I bought the car with about 170k, and it was owned by a Porsche technician for about 10 years. I have only put 20,000 on it or so in the last 1.5 years The previous owner did IMSB at 105k, and the cam chain tensioners at the same time. I know he didn't replace the main tensioner or pad though, and that one worries me. (heard lots of stories about the pin coming out and destroying the engine) It's not a perfect car by any means. It's a driver. But it's so much fun to drive that I can easily see keeping it myself for 10 years or more, and I drive the hell out of cars.

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I think that means I am going to have to split. So have to think about value of going all in or not.

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Thank you. that wasn't on my list. I'll do that.

Do the Ultimate AOS (UAOS) instead of the OEM AOS. Easier to maintain in the long run.

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Definitely!

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my take is still oil temp getting u Jeeper. Car can be slapped around at 7k all day.

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Not with loose bearings and high g turns. Airation w pressure drop is real and proven so if the motor is not in good shape it will pop.

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Will do on that one. Looks like a great solution.

OK, so building up my list of things to do to the engine. I feel I must change out the primary chain tensioner (crank to IMS), and as I can't do that without splitting the case, it puts me in a quandry. Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible. I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible. Otherwise, maybe I will just keep dropping the pan and inspecting the tensioner pad every other oil change.

you gotta leave this thing alone man. Normal maintenance will take you much further here. PM'd.

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uaos great product but nothing necessarily wrong with genuine porsche aos. Can be changed in under 2 hours. don't need to touch exp tank, manifold, alternator or engine mounts. if DIY guy i can explain how u do it and will save u $. pm me

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No question. Probably the most durable part Porsche has. Almost as durable as the water pump blades, IMSB and lukasil coating. I put them on everything i own.

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No need to worry about removing the pistons if you have the right tools and the skill to do it. But, no, you can't split the case and leave the pistons in place. You will need to pull and reinstall them.

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Haha, quality IMSB, waterpump, Lokasil, and sunvisors. Not to mention the lifetime transmission fluid. I'm a former european mechanic. It took me several hours to replace my AOS with the UAOS. If you're very experienced like PorscheTech3, you can maybe do it in 2 hours, but a DIYer, or even an experienced mechanic it will take longer. When my UAOS diaphragm failed recently, it took me 5 minutes to replace it. Unless you have several years experience working a a water cooled Porsche indy, or a dealer several years ago, I really doubt 2 (or 4) hours is possible. I'd love to watch a video proving me wrong though.

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When the Genuine Porsche AOS failed with a huge big cloud of smoke under the 50k mile Factory warranty or the 100k mile CPO warranty, Porsche insisted on replacing the engine due to the possibility of a slightly bent connecting rod that would show no apparent symptoms for several thousand miles like this car...This cars engine was torn down last week and posted on FB about the scoring on the pin side of the cylinder ( not the usual skirt side of the cylinder)The previous owner had an AOS failure , then replaced the AOS and a few other things then sold the car and the new owner found this... #6 cylinder scored on pin side of cylinder #6 rod slightly bent only about 20 thousandths I'm not saying that EVERY AOS failure will cause a bent rod or cracked cylinder, but I am saying that thousands of bent rods and cracked cylinders have been caused by AOS failures, it is just a crappy part, and is inefficient to boot...This example was just found last week.. BTW :: The new owner now has a UAOS System to be installed on his new engine..the way it should have came from the factory...

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Tex biggest thing to note is you want to just break the coolant tabs off and deal with the existing hose clamps out of the car. Your view is under bank 1's intake manifold after you unclip the solenoid that rests atop the alternator. Reach around with right arm undo vac hose and break coolant port #1, reach around with left arm atop manifold and break coolant port #2. Get under car, undo 10mm variocam bracket and get lower hose off with pull&pinch. Once off remove bolts that bolt AOS to block. Feed AOS out from the top of car behind bank 1 intake manifold. Obviously this is with everything from intake to frontmost plenum removed. Getting frontmost plenum back in with manifold still mounted is hardest part of the job, but there's a special way to do it and I'm keeping that a secret. uaos no question easier to replace. I'm a european mechanic in my head. I'm 29 but have been working on cars since I was ~12. "who's the better wrench?" - Top gun hk vs tex Edit - because you doubted me - these are from my OP where I eventually did my own aos. you need to remove coolant hose that goes to bleeder valve to give left arm room like so: Right arm fed between plenums - this is where you look just above alternator and below manifold while your arm is back there. No view unless solenoid is unclipped and moved from atop the alternator.

delete - yes uaos is great product but rod bend doesn't happen unless owner keeps driving the car. pooled oil in cylinders from failed aos is reason for rod bend and owner should replace aos/tow car immediately. there is a thread where people argue whether or not u can bend a rod just by starting the car with oil pooled in cylinders but general consensus was "unlikely"

I'd second the if it ain't broke, don't fix it suggestion. Maybe have it dynoed to see if it lost anything, but unless it burns oil or lost 50hp, I'd leave that car alone and keep driving it. Better spend 25 grand five years down the road than tomorrow.

Yep. Nothing better than being on the road or track in your 20+ year old 996 with old brittle parts that are known to fail as they age. Same can be said for the joys of being down 50 hp. Who in their right mind wouldn't embrace the joys of waiting for AAA on the side of the road.

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Just to be clear, all it takes is 1 teaspoon of oil in 1 cylinder to do a total hydrolock that shatters pistons, breaks/bends rods, cracks cylinders, d-chunk cylinder. Yes, just turning over engine with starter, with enough oil in cylinder, can cause damage that might not be apparent immediately but thousands of miles later will show up all to well.... Can't compress oil, so something (rods, cyl, piston, flattened/hammered rod bearing, etc,) has got to give.... jmo

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As others have said, no. You must disassemble the pistons/cyl to get engine cases apart. At 200k miles, your bores are way out of round/taper all the 996 experts say. The rings have now seated into OOR bores. Its not uncommon for out of round cylinders to seal and run well, as rings have worn/seated into their location. The problem comes from trying to seat new rings in old oor/tapered bores . The majority of these re-ring attempts result in wiping out the rings in a few thousand miles... IMO, do a detailed cam dev check and a detailed leak down test and a new compression check. Also try and do a detailed inspection of all chains for broken/missing cracked rollers/pieces that can jam up the pumps. Use this new information to decide what you'll do...

Does anyone remember the early on discussions 20 years ago about how the early 996.1s were prone to "D Chunking" due to how the cylinders were held by a clamp during the assembly process. The ideas of "hydralock" or "broken water pump fan" wasnt something we ever discussed. Then the issues with the frailty and limitations of the oem AOS processing oil flow took center stage. Porsche developed the Motorsports AOS as a more robust but expensive solution to the oem AOS. In Porsche's infinite wisdom, they also recommended running less oil to protect the factory aos. At that same time, solutions for on track oil starvation were also developed, imsb solutions were developed and Porsche finally found a RMS that worked after replacing countless engines. Today, the next round of improved AOS and oil starvation solutions have been developed with more iterations on the way. It became common knowledge back in the mid 2000s that you didnt want a factory AOS if you were canyon carving or tracking your car because you not only ran the annoyance of blowing smoke and oil consumption, but you also ran the risk of intermix and yes, cracking your cyclinders which also includes "D Chunking" from hyralocking. Seems that D-chunking in the early 3.4s may have had nothing to do with the clamps used in the assembly process and instead, it may have been caused by AOS failure (hydralocking) and a broken water pump blade that gets lodged in the engines causing cracking. Same for the 3.6. Go figure. I agree with those that say the 3.4 and 3.6 are very durable engines. Mjne has shown this to be the case. But history shows they can be easily improved upon and be made even more durable with just a couple of relatively inexpensive parts and procedures. If you are a talented DIY guy, you have alot more flexibility and willingness to judge the fix/don't fix decision point due to your skillset. But if you are not a DIY guy, you have to make a decision on what to upgrade or replace and when, depending on your philosophy of "proactive" vs "reactive". But let's face it, there are three parts that can go in the blink of an eye that can lead to catastrophic engine failure. (1) IMSB, (2) AOS, (3) broken water pump blade. It's everybody's call on whether they want to do something about it or not.

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You mean nothing better than spending 25 grand on an engine that runs well?

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Unless you don't mind it being 50 hp low and always on parked on the side of the road.

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What do you mean 50 hp low ? You're just making that up based on your vast non existent experience, right� I gotta give you credit, I have never seen anyone on a forum speak so conclusively about what to do and not to do with so little actual experience, remarkable. Your experience begins and ends with writing dudes checks to work on your car changing stuff they tell you to or what you read people talk about on the internet and somehow that makes you an expert in all things M96. I think what it really makes you is an Indy mechanics wet dream.

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Karen, time to take a nap. You are getting a little over excited again.

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I started by saying he should dyno it, so....

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gc do u think I could poop-a-lock my car if I blew a sh*t into my throttle body?

I haven't tried that one yet.

If you can accurately poop one teaspoon I will uhh I am not sure what the correct reward is for this

Thank you everyone for your passionate advice. I would of course prefer to not put any money into the engine and drive forever... But we all know that is a pipe dream. Next oil change (a couple of weeks from now) I will get in there with a camera and take some good imagery of the crank to IMS chain tensioner and wear pad. That will answer the question of if I need to split the block. If I do have to split it, then I would carefully ensure that the rings don't rotate on the piston when the piston is out of the cylinder, so I can get them back in their exact position again. As long as it isn't burning oil or have any scoring, I see no reason to re-sleeve. If I felt that way, I might just buy a blown engine and do it all while still driving this car, and then there would be minimal down-time. I have every confidence that the car will keep going to just fine past 200k if I do nothing... Im not looking for an excuse to spend money, but I have some plans for some very long cross country trips, and I want reliability above all else. So I think investing a few thousand $ now will extend the life of the engine and keep me from worrying about reliability in the middle of 6,000 mile trip. Thank you. I will update the thread again when I get some imagery of that tensioner.

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While it sounds feasible, once you pull the piston out of the cylinder, past the normal travel of the rings, the ring expands past ring groove/leyland. Most older piston grooves get a wear 'step' the ring seats into. Once ring expands it will never go back to how it was in the piston or cylinder. Rings normally rotate on the piston when running unless they have locator pins. Is there a chance rings will reseat once you pull them from the cylinders, yes. But its a big gamble thats up to you to bet on. Just go in knowing you might have to rip it apart again in a few thousand miles.... jmo

You could always do an oil analysis and leak-down tests if you want more information on current condition, but I would not be too worried about high mileage, especially if the previous owner was fastidious about maintenance.. As a general rule of thumb I would keep driving the car if it is running well. You wouldn't get an organ transplant if you are healthy, even at an advanced age. The exception might be if you are planning something like a long trip or other event where you absolutely need to mitigate and reduce risk.

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If rings normally rotate when the engine is running wouldn't that mean that they will continue to do so once put back into the same cilinder on the same piston? I believe only the oil control rings have a pin on the M96 to never have the ring gap end up at the low side of the cilinder where oil invariably would collect when sitting. However, the 1st and 2nd compression rings can rotate AFAIK.

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Ya, you'd think so... Just not sure ring rotation has much to do with re-seating old rings/pistons in out of round tapered cylinders. Even when matched up to same cylinders they came out of. Never really heard a good explanation of the 'why' this never seems to work out well. My guess is it has to do with the ring groove in the piston and the old ring getting relaxed and then re-compressed in a worn stepped piston groove. Thus not being able to cope with/seal oor cylinders. Seems to be a very fragile relationship good sealing old oor cylinders have with their pistons/rings. Any disturbing of this 'relationship usually proves to be not satisfactory. But thats just a guess... I know In the distant past (never on a m96) have tried at least a dozen times to seat new/old rings/pistons in worn out of round/tapered cylinders with no longevity ever. Finally, even at a tender young age, determined must be a good reason manufactures have a max out of round taper spec....

If the bores are out of round, then the rings can't rotate. All this is making me want to open it up less and less. Damn the design which does not allow the tensioner wear pad to be replaced without disassembling the entire engine! I don't want to drive to catastrophic failure though, If the tensioner is on the verge of failing, then maybe I will end up just doing a full rebuild. I'll know in a few weeks.

The tensioners r external and just screw out of the block. Not sure what the issue is here. The only componants u cant get to r the ims wear pads, ims chain and 2 long chains. Generally these parts do not fail. What r your cam deviation? If they r below -4 i wouldnt touch the motor at all. U basically have 3 viable options. Do nothing, do $2-4k in preventitive maintenance or a full rebuild. There really is no middle ground with these motors.

You might be overthinking this. Where in Florida are you located?

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The cam tensioners and pads were replaced at 105k, I am only talking about the crank to IMS chain tensioner. part: 99610516555 With 190k miles, I expect the wear pad to be nearly gone, and would like to replace before the chain starts to eat away at the paddle itself. I would like to put one of these in there: https://lnengineering.com/billet-ims...er-paddle.html I would prefer to do the few thousand dollar preventative work to extend the life of the engine, but being unable to replace a common failure part (the crank to IMS tensioner I referenced above) means that I would not have full confidence in the engine. I plan to do 2 very long trips in late '24, and early '25, that I simply don't want to be worried about the engine. So from my perspective; if I can't actually replace one of the common failure points, then am I really preventing anything? $4k in preventative work, but still have a big worry, or $10-12k for an essentially 'new' engine? Maybe I'll just take the second option.

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Space coast... Near you I believe

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Space coast is the best!

U will be more like $15-20k for a like new motor. My point is there is no inbetween with these motors. U r wecome to believe what u want but if u split the case their is no way to put it back together and have a reliable motor without a full rebuild. This has been stated many times by any of the better engine builders that pop in on this site. The ims paddle does fail occasionally but its far from a common issue. At 200k miles my motor pads all looked real good. I did all the stuff i listed earlier in the thread and i actually only had bad variocam pads and 1 stuck tensioner. 300 miles later i blew the motor due to oil starvation. I think i would be much more concerned with the condition of the bearings then with anything else considering u had no data or havent pulled telemetry from the dme. An oil anaysis should really be your 1st step. I fully agree with doing the pm on these cars but u should be getting a baseline before u start.

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I do have access to deviations, and have a reader that can see over-revs from the DME. If yours looked good at 200k, then I hope mine does as well. I will check. You have experience with an engine of the same age/milage, so I do appreciate your input. I believe you when you say there is no way to split the case and have a reliable engine. The $12k I estimated was based on doing all the work myself. (aside from the machining, and valve seats and guides.) Reasonable?

Precovid i was at $12.5k in parts with nickasil bores..... it all depends in what options u choose and parts avalability. A porsche short block and heads done by hoffman may be the best solution for a nontrack driver. I think u can be all in for under $15k with no fear of binning the rebuild. These motors require some special tools and the rebuild video by Raby is a must.

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gotcha. Yep then I see why you would say $15k Prices surely have come up. Here is hoping the wear pad is in good shape then.

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Many pictures I've seen online indicate our crank bearings are worn through long before reaching 200k miles.

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The second ring is pinned on the factory pistons. The top and oil controls are free to rotate. No aftermarket piston manufacturer, even Mahle Motorsport, offers pinning.

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From my perspective, @ 200k, your engine doesn't owe you a thing. Its treated you and previous owners to more than many 996 owners ever get, by double or triple. To throw in my 2cents, no you are not preventing anything by replacing a few parts that are still working on a 200k m96, 1 time use m96 blocks. Drive it and enjoy it. Replace broken parts when needed if it makes sense. @ 200k doing a long trip is a gamble. Only 1 way to get a confidence inspiring engine @ 200k. If you must have a long trip dependable car, must go whole hog or nothing with a m96, just as DJ said. Imo, 15k is a pipe dream even for a diy m96 engine build. Sleeved big bore nik'd cyls,,,You wont get out of LN for less than $7500 after shipping and tax and maybe a few small parts like oversize head gaskets, etc. 200k m96 Heads at Len H, are going to cost you $5000 after seats/guides/springs/mild porting/maybe a valve or 2/etc. Just saw a set of his stage 2 996.2 heads. WOW, They looked insanely well done, impressive. I've seen/done lots and lots of HP heads, imo heads are where power is made,, these are some of the best I've ever seen. Should let all the available power+ be delivered with crisp throttle response. m96 engine builder (Charles) Experts say, 1/2 the cranks they see are cracked. New cranks are $6000, reconditioned cranks are $4500 if you can find 1. Now add in all the normal rebuild parts like bearings, Rods?, DMF, clutch, arp fastners, gaskets, imsb solution, oil pumps, valve train components, etc... Then throw in a nice balance job and maybe a HP set of cams.... Yup, with a short block from the dealer, it would save some, especially if your crank is bad. But you still have the problematic loco-sil defective structure block. Some have developed bore score/IMSB/RMS problems in under 30k on oem blocks. And if you ever have a problem with chains or other parts that need to split the cases, you're in the same boat of 1 time use cylinders. With nik-sil cylinders you have a reusable block. Clean off the aluminum from the nik cross hatch with some muriatic acid and you're ready to go again. If there is some small wear, diamond hone the Cylinders and you're ready to rebuild/disassemble/reassemble, unlike oem loco-sil 1 time use blocks. jmo

I keep thinking about @911user who got almost 500k out of his M96 without real issues and would still be going if he hadn't passed away in an untimely manner.

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Maybe consider speaking to Dan at the Werkshop in Melbourne, FL before making any big decisions. You will get an honest assessment and he is not a shop that is under-booked for work.

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You might be 100% correct. The whole debate of how much and when rings do rotate has been argued for many years...

This thread is full of retardation, hence my poopy comment. OP your car is fine. You are going to introduce more problems than if you were to just do normal stuff, change the oil, and drive it. It will last well beyond 300K. If I were a betting man (which I am), I'd give it past 400K. The car is laughing at 200K and 90% of what is posted on this thread is the typical 996 fear-mongering that I've come to learn is all BS.