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 the heat generated by the engine makes 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 bearings 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 effect 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 too 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 unburnt fuel to evaporate off.
A common job here at OCD Porsche Specialist.....here is one job to show a 996 engine & Gearbox out due to it being a Tiptronic model.