IMS bearings

I am looking at acquiring a 2004 Porsche 911 Coupe C4S and hear stories out “IMS and RMS bearings” and that these cars are very susceptible to damage to catostrophic failure - which can happen without warning at any time in the engines life. Any advice as to how to check the car out and are there upgrades to remove this kind of failure? Thanks, David

Hi David, Those with a more detailed knowledge/experience will undoubtedly chip-in here, but there’s no doubt that the internet has contributed to overplaying IMS failures. I recall speaking to a very experienced Porsche master technician at a dealership who’d never experienced such a failure! An imminent IMS failure is more difficult to diagnose [metal particles in the oil and filter?], but a failing RMS is more easily detected by a visible leak at the engine/transmission joint. A light misting generally isn’t considered to be a problem, but if oil is dripping from the joint it’s time to replace the RMS. A number of IMS upgrades are available from reputable Porsche Independents [Google is your friend!], but here’s a typical example: Porsche IMS Bearing Replacement and Upgrades - RPM Technik - Independent Porsche Specialists Upgrade your Boxster, Cayman or 911 IMS bearing to ensure your Porsche avoids the dreaded IMS bearing failure. Call us today on +44(0)1296 663 824 to make a booking. rpmtechnik.co.uk As you can see, it’s worthwhile changing the clutch if you’re contemplating a RMS and IMS replacement. Unless you’re buying a car from an established Porsche seller or a Porsche Independent, both of whom should have carried out a detailed pre-sale inspection, I would always advise an independent pre-purchase inspection since this should identify any potential problems with the car. Jeff

Hi Jeff - really appreciate the prompt and detailed explanation. As you indicated, if you read about IMS on the internet it sounds like all Porsche 911 from 2000 onwards were dropping by flies with metal chips in the oil pipes. The upgrade link will be very helpful. Thanks, David

Pleased to hear that was of some use David. Just to add that another factor with the 996 and 997 Gen1 engines is the subject of bore scoring and cylinder cracking. Once again the internet has played its part in overblowing the extent of the problem, but there’s no doubt that these engines are prone to these issues, the exact cause of which is far from clear. Fortunately this is something which can be checked without stripping-down the engine, and a number of Porsche specialists are able to do this by inserting a small camera through the sparking plug holes to inspect the bores. This could form one part of a PPI on a prospective purchase. Companies like Hartech are able to re-sleeve the cylinders and rebuild these engines, although a full engine rebuild will be very expensive. They’re a very experienced and reliable rebuilder with an excellent track record. Common Porsche Engine Faults - Hartech The typical problems affecting Porsche water cooled engines from 1997 to 2008 are: Scored Cylinders Cracked Cylinders IMS Bearing Failure Crank Bearing Failure www.hartech.org Jeff

David The 911 - 996 C4S is a very good car and you could check out the buyers guide in the 996 Register section. I would also strongly recommend the facebook group " The Original Porsche 996 Carrera Owners Club " as there are genuine owners on there as well as a lot of saved good advice. Not sure what part of the country you are in, but there are a number of us that would answer any questions you may have as well as recommend events and suppliers where we can. Between the POC and 996 group you are well stocked with information. Ian​

RMS is Rear Main Seal ..nearly every engine has one , it's a seal where the crankshaft exits the case. A leak at the engine to gearbox joint is often put down to this but quite likely to be the IMS bearing cover seal !

One of the things to watch out for is a history of over-revving the engine. Although these engines are rev-limited, it is possible to over-rev an engine with an accidental change down at high revs or due to power remaps. 996/986 models had different over-rev ranges to the later models, see https://911virgin.com/engine-revs/ . A good Porsche specialist or OPC should include an over-rev report. Over-revs due to a mis-slotted gear puts a sudden additional strain on the IMS and valve gear, especially chains. Over-revs could be a factor in many of the reported failures, although the owners may be in denial. It may be significant that few, if any, IMS failures occur on cars with automatic transmissions. There is no question that M96 engines have some weaknesses which were eliminated with the MA1 engine from model year 2009. Have a prospective purchase inspected by a good specialist or an OPC who will include an over-rev report. Frequent over-revs in a high range should be a concern, perhaps indicative of hard track-day use.

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Good evening David I have just purchased a 996 4s with 63k on the clock,for my own piece of mind I had a EPS ims bearing and rear main seal installed by Green Car Porsche, if you are doing the bearing I would consider taking their advice on changing the overhead brake pipe mine was heavily corroded at the same time

Apologies in advance to everyone for raising the IMS issue again. I'm aware you can obtain numerous third party replacement bearings as per the link helpfully posted above, however my question is does Porsche still not offer an official solution to this? My 996 which we have owned since new has only ever been maintained by the OPC where it was bought and they have never mentioned it, but I find it slightly worrying that my car has the original IMS bearing that could theoretically fail without warning, destroying the engine in the process, although I appreciate it is rare. Surely if third parties can develop a replacement, Porsche could?

There is no official Porsche retrofit replacement. The internet has amplified the severity of this problem which actually only occurs on a very small number of cars. When cars were almost new and under warranty, there was no aftermarket solution so Porsche simply fitted a replacement the engine, but not necessarily in every case. The exceptions were where diagnostics showed that the engine had been repeatedly over-revved, in which case a warranty claim might be denied. Modern engine control units include a rev-limiter which, in normal use, will prevent over-revving the engine beyond safe limits. If a manual up change of gears at high rpm is, accidentally, slotted into a lower gear, engine revs will be forced higher, beyond the limit set in the engine control system. This overspeed will be permanently logged by the on-board systems. When an engine is over-revved, loads applied to components will exceed design specs. Stretched timing chains and, in the case of the M96/M97 engines, overloaded IMS bearings are amongst the possible consequences. Since you have owned the car from new, you will know the full history of the car and, hopefully, it has never been seriously over-revved. You can ask your OPC to check this using their PIWIS equipment. PIWIS will also detect if there are valve timing anomalies that would be an indication of worn or stretched timing chains, worn or damaged chain tensioners, or other wear in the camshaft drive system. The fact that your OPC has never mentioned any issues suggests that they have no concerns. Assuming the car has neve been abused and has had regular oil and filter changes, there should be no cause to worry about your IMS bearing. If you are still concerned, visit a reputable specialist for their advice. Retrofitting a proven third party solution is not a negative against the car, most people would consider it a positive move.

Thank you for such a comprehensive answer, that is very helpful. I have always treated it very carefully and in fact it has only done 13,000 miles. I will discuss the points you mention however at the next service.