How many pre-2000 996s have nikasil bore liner problems?

I'm looking to buy my first 911 and have been tempted by some very reasonable prices around. There's 1998 996 with 96k on the clock for 13995. Its had £7k worth of engine work done by Porsche when the mileage was 60000 so assume that this one is good to go. Then there's the other one, a 1998 with 76k miles for £14250 , usual full history but not sign of major work. Which would be the better buy assuking everythigns else is equal? Go for the 98k miler safe in the knowledge the engines been rebuilt (from a trader) or risk a lower mileage private car albeit with good history. Would the nikasil problem have reared its head by now or could it manifest itself at any stage? How would I know what to look for? Your help and advice will be gratefully received. Rich

The engines are generally good for 120k miles and it's about this mileage that the internal chain belt is designed for. Who rebuilt the engine and did they put any upgraded components in it? If you're worried about it, look at going on a Hartech scheme (assuming you're near Bolton) as they do an all-inclusive warranty and maintenance on a fixed monthly fee.

My understanding is that the 996 engine will fail at 40-odd thousand miles if it is prone to fail, and not that many are/were in any case (failure may be liner slippage, intermediate shaft failure, or rms leak although leaking rms is not so much an issue in itself but may indicate something more sinister such as shaft misalignment, hence lasting to 40K miles only) so the 76K miler might be safer unless the rebuilt has been done properly with upgraded bits. Apart from this go on condition & think about the other bits that typically wear (clutch, brake discs, suspension joints/arms/bushes, corrosion of rads etc.). I have a friend with an early 996 with 140K miles & (touch wood) has had no problems.

I believe the nikasil bore liner warps over time, so just eventually goes. The Hartech rebuild replaces this liner with a stronger/thicker type (I think from the GT3/Turbo engine, but might be mistaken). If it has upgraded parts, eg. liners, intermediate shaft etc, then I'd go for the higher mileage one. If it's just been replaced with standard parts, then I'd go for the lower mileage one. Do you know exactly what work was carried out on it and by whom?

[anorak] 996 Carrera liners are Lokasil, not Nikasil. [/anorak]

Lokasil not nikasil, well forgive my ignorance! The 98k car has had the work done by Porsche out of interest. Thanks for your feedback btw guys.

"How many pre-2000 996s have nikasil bore liner problems?" The water coooled Carrera's have NO liners. They have impregnated Lokasil, the hybrid cooled GT3 and Turbo (+ derivs GT2 etc) have aluminium sleeves coated with Nikasil. The Lokasil is a silicon hardening process for the aluminium castings. Porous cylindrical shells of silicon are aligned in the cast where the cylinder walls will be and when the molten aluminum is poured in it reacts with this LOCAlised SILicon matrix. The silicon "bleeds" into the local surrounding aluminium. The cooled cast is machined and acid etched to create smooth and hard cylinder walls. Because the Lokasil is part of the cast it cannot "slip". As the GT3, Turbo (GT2) are hybrid cooled (water cooled heads, air cooled bottom ends and cases), they have a different design so the air, oil and water stay separate. The case has a sealing liner coated with Nikasil. (NICkel-SILicon carbide). The incredibly hard Nikasil was first used by Porsche in 1970 for the 917 aircooled engines to allow smaller engineering tolerances, allowing greater pressures and bigger power. One problem the Lokasil engine design can have is catastrophic edge failure. The casting of the tube (cylinder wall) is squared off at the end. By this I mean the tube just ends perfectly straight. This means a very sharp right-angle edge with the associated point stresses and aerodynamic/hydrodynamic vortices. The edge can get fatigued and break off, this in itself is not ideal as piston sealing may be jeopardised, the real issue is where the broken cylinder wall fragments end up next in a fast moving engine. The debris will destroy the pistons, conn rods, crank shafts etc and complete engine destruction ensues. Fortunately it is pretty rare. A more common failure of the casting is not related to any liners or lokasil etc, it is the thin walls associated with cross-flowed water cooling and large bore. Apparently (according to Hartech) eventually ALL water cooled Porsche flat sixes will become ovalised over time (warped). Including Boxster. For both, the solution is a re-bore with liners. Autofarm will machine out your watery 996's Lokasil and insert their version of the hybrid Nikasil liners (with rounded/tapered edges) for £3,385+£1,400 (engine in/out labour)+VAT if you are really worried. But £5,500 is getting on for a good subsidy towards any unlikely engine explosion. Not sure what Hartech charge for their liners.

GT4, that was most useful and will allow me to sleep better... or will it?? Could you share the same level of knowledge you probably have about the intermediate shaft; what does it do & why does it occasionally fail? Thank you in anticipation :thumb:

Wow some excellent stuff here thanks so far. Out of interest I went to see the 76k miler and it was a really clean, well cared for 911. It had been serviced a week ago by Porsche themselves in Towcester. The only thing I found wrong was a little bit of emulsification inside the oil filler cap. Given the car has just been serviced by Porsche should I be worried about this or not? :?: If not then it's all mine!!!

AFAIK 997.2 has no IMS, 996 TT/GT2/GT3 have half an IMS (it is a different design again) The IMS runs the "ancilleries" - ie oil pumps, variocam, alternator (?) The most important is the variocam, if IMS fails the cams fail and valves fail. ie engine blows up! The IMS has two or three faults, 996.1 and 996.2 are quite weak shafts (997 are beefed up considerably), 996.1 have the fewest and least well oiled bearings (the number of bearings was upped for 996.2) The shaft weakness can lead to snapping. The oiling issue can lead to seizure. Autofarm will fit the 997.1 IMS with 996 splines for 850 (plus cost to crack it open and VAT) Just for completeness, the IRS collects US tax

If the Mayo (do search) is from condensation this is "normal" (and to think some of these vehicles retail for 100k plus!). It is not harmful. The caveats being: is it definitely not Head Gasket related? and the above "normal" comment is not an approval to buy the rest of the car. If a sensible suggestion on a forum steers you away from a potential lemon all good. But a sensible suggestion on a forum not steering you away from a potential lemon is not a guarantee of happy motoring. (shares can go down as well as up etc etc) The best advice (in 98.4% of replies) is get a PPI or OPC 111 point healthcheck before a purchase.

The Intermediate Shaft drives the camshafts. That's why it is catastrophic if it fails. Variocam changes the cam timing and a v-c failure doesn't normally cause anything other than rough running. The alternator is driven by the ancilliary polyrib drive belt. (Serpentine belt).

Thanks for clarification, I meant the whole cam/valve system (hence my comment re failing cams and valves) I wasn't sure of alternator hence (?) in my reply. In any case the IMS failure is catastrophic as it leads to engine failure due to cams and valves failing.

5.5k for liners , I would rather pay a bit extra and get a whole new engine in the unlikely event I needed one. Then you would get warranty on the whole lot. It seems false economy to throw that sort of money at a worn engine.

+1 A complete Autofarm rework will cost £8000+. The Porsche exchange engines are subsidised and cost about £9000, and they come complete with all ancilliaries, ready to fit, including oil. I'm convinced they are brand new - they certainly look it - and as you say, have a 2 year warranty. A no-brainer IMHO. Autofarm seem to have gained all the kudos for their rebuilds, but the block/liners were developed by the old Perfect Bore company in Andover. (Now Capricorn Automotive). Barry Hart (Hartech) has some good options for strengthening the engine, which are a bit more cost-effective. Once the've gone bang they are a basket case though.