There is a colossal amount of discussion and information on the internet about IMS bearing failure. While some of it is actually true, most are stories by people who have had a bad experience. Here are the basics you need to know….
Porsche is well versed on IMS design and application and has been using it for a long time. In fact, every 911 ever built has an IMS. In the early engines (pre-1997), the IMS do not present failure related issues and perform the same as M96 and M97 engines (1997-2008), however, the IMS bearings in the M96 and M97 engines are problematic.
The intermediate shaft is driven by the crank shaft via gears. There are two IMS bearings for each Porsche engine. One drives the left cam shafts and the other drives the right cam shafts.
The IMS bearing on the front of the engine is integrated into the front oil pump and receives pressure fed oil for lubrication. This design results in maintenance free operation. However, because the IMS on the transmission side is situated closest to the flywheel, it does not allow for pressurized lubrication. As a consequence, this particular IMS bearing has been criticized for having a high failure rate. More importantly, although this bearing was designed to operate in the absence of pressure fed oil and instead operate in the air this design is problematic because the “sealed bearing” is not capable of withstanding the environmental conditions of an operating engine. Some experts have reported that all M96 and M97 engines from 1997 through 2008 will eventually suffer an intermediate shaft bearing failure, that’s right it will fail.
Additionally, the experts have arrived at a consensus on factors that will adversely affect the life of an IMS bearing, including:
• Inadequate design – Nothing you can do
• Poor lubrication – Nothing you can do
• Long oil drain intervals - change your oil every 3K miles or every 6 months
• High fuel and H2O content in engine oil – Use the entire RPM range and avoid short trips
However, LN Engineering offers three IMS Retrofit solutions. Two of the three can be done without disassembly of the engine and include installing a:
• Single row IMS Retrofit™ kit (fits MY02-05 M96 engines including some MY00-01)
• Dual row IMS Retrofit™ kit (fits MY97-99 M96 engines including some MY00-01)
• MY06-08 IMS Retrofit™ kit (fits MY06-08 M97 engines, requires engine disassembly)
In 2009 the M97 engine was discontinued and replaced with the 9A1 engine. The 9A1 engine is commonly known for Direct Fuel Injection (DFI), but it also lacks IMS, instead the cam shafts are driven directly off the crank shaft.
While I am not going to belabor the point, you can find a wealth of information on the web, at performance shops, and local Porsche service departments. However, if you have specific questions on how the IMS bearing failure rate affects your particular vehicle I would recommend you review the May 2013 edition of Panorama (pg. 96)ner, Alex Raphael, directly at (360) 373-6758.