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Liquid Cooled M96 IMS engine retrofit part 2


Feed back on the liquid cooled late-model Porsche engines has been mostly inquiries and requests for preventative measures. To repeat, more frequent oil changes, especially for low mile, seasonal use cars seems to be the best prevention. With early detection, by way of listening for whirring, a grinding noise that was never there before and/or, an oil leak in the area of the clutch bell-housing and rear main seal area being the next best.

The photos accompanying this follow up article show parts from a 2004, 996 with 24,000 miles, never tracked, one owner, six year old car. Without warning the intermediate shaft bearing seized and broke the support shaft. As mentioned in the first article, Porsche recognized the inherent weakness in the rear bearing of the intermediate shaft. In mid 2005, der factory issued a bulletin that the support plate and bearing had been updated, and that any engine that may be apart for other reasons, be retro-fitted with the larger 10 mm bearing support (up till then it was 8 mm)


The engine featured here had the 8 mm bearing and cover. Note the damage caused by the errant ball bearings. Look closely at the bearing races. As the bearing began to fail, the rear of the auxiliary shaft which is DRIVEN by the crankshaft began to wobble. This oscillation could not be controlled by the drive chain tensioner and eventually snapped the tensioner guide shoe in half.  Directly next to the main DRIVEN chain is the DRIVE chain and sprocket for bank one camshafts. The oscillations became so severe, even at low engine speed that the intermediate shaft DRIVEN chain proceeded to jump timing, followed by the bank one chain. This caused the camshafts to become out of phase with the crankshaft and pistons. This severe out of time condition then caused the pistons to contact the valves, bent the valves and boom, done deal.


We have been using the newest 10 mm stud upgrade from Stuttgart on all of our street and race engines since 2005. We have not experienced a failure that we are aware of. Replacement of the entire shaft using the factory piece requires removal and complete disassembly of the engine. However, LN Engineering, whom we provided a link to in the last article, ( ) has come up with an in car fix (before it fails totally as above). This repair is preventative and can be done while performing a rear main seal or clutch replacement. As outlined in their procedure, identification of the type of bearing is critical. One row, two row bearing makes a difference. We have performed this essential upgrade, engine in car, and have had excellent success.

Photo 218 shows a few intermediate shafts that we have on hand ready for installation
Photo 219 shows the improved Porsche bearing on the left with 10 mm shaft; the 8 mm older style is on the right
Photo 220 shows what the bearing race looks like after it failed
Photo 221 shows all of the broken pieces, ball bearings, failed 8 mm center shaft, rear plate and inner bearing race


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