Porsche M96/M97 Intermediate Shaft Bearing issue new article content ...
The Intermediate Shaft Bearing
The M96/M97 engines in Porsche's 996 model used an Intermediate Shaft ("IMS") to transmit power from the crankshaft to the camshafts. One end of the IMS is held in place by a plain bearing, the other by a roller bearing, with the roller bearing at the front of the engine, behind the transmission. Three types of roller bearing were used over the engine's life: dual-row roller until 1999 and in some 2000 and 2001 cars. Starting in model year 2000, Porsche began phasing out the dual row bearing and went to a smaller single row roller bearing, with significantly less load capacity[1]. From MY 2006 the IMS bearing remained single row but is of a different design that cannot be replaced.
Failure of the IMS bearing leads to failure of the timing gear and potentially destruction of the engine. Failure rates of 4-10% were cited in the US Class Action lawsuit (see below).
Causes of IMS bearing failure
The IMS bearing is a sealed unit. It is submerged in engine oil when the engine is shut off or idling. When the car is at speed, the sump level drops and the shaft rotates in an oil mist/splash lubrication environment[2]. Some engine failures appear to be due to engine oil contaminating the bearing and washing out the grease contained within it, increasing wear of the balls and ultimately failure of the bearing.[3]. The bolt retaining the IMS bearing is also known to fail, which also leads to IMS bearing failure. Thirdly, poor timing between cams and crankshaft may contribute to unusually high wear on the IMS bearing, eventually leading to failure.
Preventative maintenance
IMS bearing failure rates are low, probably <10% of the total cars manufactured. Accepted solutions to prevent IMS bearing failure are either to replace the original bearing as a serviceable item, or to upgrade either to a ceramic-metal hybrid bearing, or a plain bearing lubricated by a forced oil feed. Where roller bearings continue to be used some people like to remove the bearing seals to allow oil to lubricate and cool the bearing.
Maintaining good cam timing could also help reduce camshaft deviation therefore stresses on the IMS and its bearing.
MY 2006 to MY 2009 cars
Cars made in 2006 to 2009 model years (potentially anything manufactured from 1st January 2005 to the end of the 997 model life) received an unserviceable bearing type. For these cars it is recommended to remove the bearing seal to allow oil to lubricate the bearing.
US Class Action Lawsuit
in 2013 PCNA settled a class-action lawsuit brought by Bruce Eisen et al, without accepting liability. The lawsuit sought compensation for owners of MY2001 to MY 2005 Boxster and 996 cars that had experienced an IMS failure. Details[4]
Porsche agreed to compensate owners of cars made between 4th May 2001 and 21st February 2005 who had experienced an IMS bearing failure within the first ten years of the car's life, or 130,000 miles, whichever came first. Owners who had changed the IMS bearing as a preventative measure were also eligible for compensation. Note however the schedule of payments was weighted heavily in the favour of cars purchased through the Approved Certified Pre-Owned Program ("ACPO").
Original owner | ACPO purchaser | Used Not ACPO | |
---|---|---|---|
Up to 50,000 miles | 100% | 100% | 25% |
50,001 to 60,000 miles | 90% | 100% | 25% |
60,001 to 70,000 miles | 80% | 100% | 25% |
70,001 to 80,000 miles | 70% | 100% | 25% |
80,001 to 90,000 miles | 60% | 100% | 25% |
90,001 to 100,000 miles | 50% | 100% | 25% |
100,001 to 130,000 miles | 40% | 40% | 25% |
References
- ^ oregonpca.org https://www.oregonpca.org/wp-content/uploads/2014/06/ORPCA-IMS.pdf. Retrieved 6 August 2017.
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(help) - ^ Grassrootsmotorsports.com https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/the-frugal-mechanic-meets-a-porsche-boxster/120457/page2/. Retrieved 7 August 2017.
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(help) - ^ Dempsey, Wayne. "Boxster Intermediate Shaft Bearing Replacement and Upgrade (IMS)". Pelican Parts. Retrieved 6 August 2017.
- ^ Eisenimssettlement.com http://eisenimssettlement.com/docs/sa.pdf. Retrieved 6 August 2017.
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