All 996 engines have an intermediate shaft that runs the length of the underside of the block and is chain-driven from the crankshaft. This, in turn, drives the twin camshafts on each bank of cylinders. At the end of this is a sprocket which turns on a bearing. The sprocket is retained by a small stud that can break, causing the bearing to fail. At first, this manifests itself as a noisy rattle, which turns into a death rattle as the cam chain come off, leading to further internal damage. Porsche changed the design of this shaft no less than four times during the life of the 996; partly to solve the bearing failure issue, and partly to reduce an annoying rattle on start-up. Later types, therefore, have a larger bearing and a redesigned sprocket designed to mate with a special toothed chain, whereas the early ones drove a conventional double chain. Because of this, it is not possible to fit the later type intermediate shaft to an early engine without also using a later-type crankshaft, which will work with the toothed drive but is an expensive solution. So you have to fit another early-type shaft which may, of course fail again. Incidentally, failure of the intermediate shaft bearing can also lead to an oil leak from the front end of the engine, because of an accompanying failure of the oil seal. What’s more, the flanged end of the shaft is secured to the end of the engine with three bolts, the holes for which project right through the end of the engine and so oil can seep through these, too, if the threads aren’t sealed with locking compound. unfortunatly to fix the problem if its too late requires a new engine, we can however rebuild the old engine dependant on how severe the damage is.

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