User manual PORSCHE 968 ASSEMBLY INSPECTION PROCEDURE AND MAINTENANCE SCHEDULE

[. . . ] Porsche 968 Variocam Assembly: Inspection Procedure and Maintenance Schedule Background There have been a number of documented failures relating to the Variocam mechanism fitted to the Porsche 968. Porsche has not published any periodic inspection or maintenance requirements for the Variocam. Consequently even cars with a full Porsche main dealer service history may suffer undetected excessive wear or even catastrophic failures. In the worst case this will result in bent valves and major engine damage. [. . . ] Place rags beneath connections on two fuel hoses at rear of cam cover (see figure 1). Undo both fuel line connections using 17mm and 19mm spanners. Take care to ensure that the fittings nearest brake master cylinder are held stationary and not twisted. Note: a few ml's of fuel will be spilled during the process, hence the rags. Gently pull fuel lines clear of the cam cover, taking care not to kink the lines. Pull out spark plug caps/leads and remove spark plugs. Insert clean rags into spark plug recesses to avoid risk of dropping loose objects into cylinders. Unscrew 13 hexagon socket head screws securing cam cover. Note that these screws do not need to be removed from the cover once released but be aware that they are not held captive in the cam cover and may drop out when the cover is removed. Gently pull on the cam cover to release its seal. It may be necessary to apply leverage but be careful and do not insert any sharp objects between the sealing faces. When the cover is loose, gently pull away from the engine. The black rubber seal can either stay in place on the engine, or stay attached to the cam cover. When withdrawing the cover, it's often needed to peel the seal away from parts of the engine or cover. IF COVER SCREWS ARE STILL IN THE COVER, TAKE CARE THAT THEY DON'T FALL OUT AND DROP INTO THE EXPOSED ENGINE!Note that there are four black circular rubber seals around the spark plug recesses. These will hopefully stay attached to the engine when the cover is removed but may pull away with the cover. With the cover removed, the inspection can begin. Take great care not to drop anything into the engine, as there are oil drain galleries below the exhaust camshaft and screws, dirt, or small tools can easily find their way into the engine. If this happens, you will need to remove the oil pan to recover them!Using the light source and mirror, carefully and methodically inspect the upper and lower tensioner pads, both camshaft sprockets, the metal oil pipe feeding oil to the tensioner body, and the shiny piston rod of the upper tensioner for wear or scoring (see figures 2 & 3). These checks are very subjective, there is no test gauge or tool to measure anything. [. . . ] In normal wear, the grooves have an "even" surface. If you have rough surfaces, clearly visible in Figure 4, immediately change both pads. To avoid major problems, change pads every 8 years, even if the "wear limits" are apparently not yet reached. The chain stretching can be measured easily and precisely only by dismounting the old chain (requiring removal of both camshafts) and comparing it with a new one. [. . . ]