Porsche 996 & Boxster Intermediate Shaft Bearing Failure (IMS Failure).
The IMS bearing on Porsche M96 engines fitted to the 996 & Boxster have gained a reputation for failure, although in reality it does not happen to all of them. The problem is made worse by the fact you get little or no warning that a failure is imminent and due to the affect a failure has on the valve timing the end result is usually catastrophic, in some cases the damage is so server that it is uneconomical to repair. If you read the various Porsche forums on the internet you will get a feel for the failure rate, although it is worth bearing in mind that it is far more likely that owners that have had problems are going to comment than those that have had years of trouble free motoring.
Why does it fail ? Well there are many suggestions for this, but the most credible seem to be a lubrication, poor design and increased length of service Intervals. The bearing used by Porsche is a sealed type bearing more commonly used in applications outside the engine, the bearing is filled with grease during manufacture and then sealed in with a seal either side of the bearing, Over time with the heat generated by the engine the seals go hard and the grease contained within the bearing seeps out but the seals prevent engine oil getting in to lubricate it. Many have suggested that the seal on the outer edge of the bearing should be removed when fitted so allowing the engine oil to lubricate the bearing The intermediate shaft has been used by Porsche for many years, but on previous engines a plain engine bearing was used (similar to those used for main and big end bearing) and the bearing was lubricated by an oil supply from the oil pump, these bearing could wear and lead to noise, but most importantly they did not cause a catastrophic engine failure. Porsche like most vehicle manufactures have increased the interval between services, this has the affect of making the maintenance cost over the first three or four years of ownership cheaper, which is particularly attractive to leasing companies. Although oil technology has improved over the last twenty years, the by-products of an internal combustion engine have not! The result is that the lubrication ability of even the most expensive oil declines over time, as the oil is degraded with un-burnt fuel and carbon. Porsche dealers are now seeing piston and liner damage on late 997 engines, only time will tell but perhaps this to is caused by degrading of oil. Having spent in excess of seventy thousand pounds on a fantastic piece of German engineering do you really need to save a few hundred pounds by leaving the oil in the engine for two years or twenty thousand miles. We would suggest an oil change at least every year or better still every six months, particularly if you are doing very short journeys, where the engine does not get up to full running temperatures, giving the chance for un burnt fuel to evaporate off.
So what can be done? You can't buy a replacement bearing from Porsche, you have to replaced the whole intermediate shaft which involves removing and completely stripping the engine. We started to look at the possibility of sourcing a replacement bearing, during our research we came across LN Engineering who in conjunction with Flat 6 Innovations (both based in the USA) have developed a repair method and parts for the replacement of the Intermediate shaft bearing, using a stronger ceramic bearing offering up to five times the service life of the original bearing. Having looked at their product, method of fitment and the large number of USA Porsche specialists using it, there seemed little point in us reinventing the wheel! So we can now offer their system of repair / prevention.
Over the life of the M96 and Later M97 engines, three types of intermediate bearing have been used MY97-99 a duel row bearing was used and can be changed without stripping the engine, from MY02-05 a single row bearing was used, (in many ways this bearing was a retrograde step) this bearing can also be changed without the need to strip the engine, During the period MY99 -02 you can find either of these bearings. From MY06-08 the bearing is bigger and can't be removed without removing and stripping the engine.
It is felt by LN Engineering that the single row bearing used from MY 02-05 has a lower capacity and they feel that it should be replaced every four years or 50,000miles, which corresponds remarkably with our experience of IMS failure, the vast majority of the total failures we have seen have been on this year range of vehicle, two of which were on MY04 Boxster S one with 16,000 miles and the other with 26,000 miles, both had full service histories and were only used as normal road cars.