Porsche intermediate shaft bearing failures are one of the most talked about issues with the 996 and 986's with the M96 engine. During the design and product selection process Porsche chose to save a bit of money by selecting a lesser expensive bearing that was "good enough". Time has proven, however, that the bearing selected was simply not up to the task and the resulting failures have cost owners huge sums of money.
The intermediate shaft bearing is located at the rear of the engine and is accessible with the flywheel removed. The bearing serves to locate the rear portion of the shaft that drives the engines timing chains. A complete failure can cause the shaft to be able to move potentially allowing the timing chains to loose tension and jump on the gear ultimately allowing the valves to contact the pistons and cause severe engine damage.
There is unfortunately no way to predict nor analyze the status of the bearing without removing it, and to make matters more confusing the failures seem to be very random. We have seen a well maintained Boxster have a catastrophic IMS bearing failure with under 40,000 miles and have changed a bearing in a 996 with over 100,000 miles that was still in good condition. Our recommendation is to get the bearing changed sooner rather than later to remove the concern and that it's unwise to replace a bad clutch without also doing the IMS bearing.
There are two versions of the bearing used by Porsche and therefore two versions of the upgraded bearing to use depending on when the car was produced. The early bearing used from 1997 986 and 1999 996 uses two rows of ball bearings and is refered to as the double row bearing. Model year 2000 and 2001 cars could have either the dual row or the later single row bearing installed and to correct replacement can only be determined by inspecting the bearing installed in the car. From model year 2002 all 996 and 986 models have the single row bearing and require a single row replacement IMS upgrade.
Because the IMS bearing replacement requires removing the transmission, clutch, and flywheel there are several parts in the same area that we recommend replacing at the same time.
Since the clutch and flywheel must be removed there is an obvious option for upgrades at this time if desired as there is no additional labor cost associated with installing new/upgraded parts instead of reinstalling your existing clutch and flywheel. Clutch pressure plate and flywheel bolts are replaced either way as they are one time use (torque to yield) bolts.
The M96 is also known for oil leaks at the rear main seal and rear of the engine case. These problems can be solved, and prevented from occurring down the road, by replacing the RMS (rear main seal) and the 4 bolts that hold the engine case together with updated parts manufactured to a new specification as specified in service bulletins from Porsche. One other common failure item is the air-oil separator located on the rear upper portion of the engine. This part is responsible for keeping the engines oil vapors from getting in to the intake. It's failure can cause problems as small as a tiny puff of smoke at startup up to a complete engine failure due to the intake being flooded with oil. On a 986 (Boxster) this part is easily replaced at any time and shares no labor cost with the IMS bearing, but on a 996 (Carrera) this part can be replaced for an hour of labor cost versus approximately 6 hours when done by itself with the transmission installed.
