Porsche 968 - ASSEMBLY INSPECTION PROCEDURE AND MAINTENANCE SCHEDULE Maintenance Manual page 6

17. In order to check the sprockets fully, it is necessary to turn the engine through
two full revolutions. Remove the rags inserted in the spark plug recesses.
18. Attach the 24mm deep 6 point socket and ratchet handle to the main
crankshaft pulley bolt. The bolt is hidden from normal view by the pulley.
19. Using the ratchet handle, slowly rotate the crankshaft in a clockwise direction
when viewed from the front of the car looking backwards. DO NOT
ROTATE THE ENGINE IN AN ANTI-CLOCKWISE DIRECTION.
20. As an alternative, the engine can be rotated (manual transmission only) by
placing the car into a high gear and pushing the car forward. DO NOT PUSH
THE CAR BACKWARDS. Because this method does not allow such fine
control of crankshaft/camshaft position, the socket and ratchet method is
preferred.
21. Rotate the crankshaft sufficiently to turn the camshafts so that previously
hidden teeth on the sprockets can be inspected. Continue until all teeth have
been properly inspected (requires two complete crankshaft revolutions). Any
missing or badly damaged teeth will require camshaft replacement (see figure
3).
22. Whilst missing teeth are easy to spot, it is more difficult to judge the amount
of wear on the sprockets. In many cases there will be some slight marking and
pitting/galling of the sprocket teeth. Look for signs of cracks in the faces of
the teeth where the chain rides. Carefully study the photos of my badly worn
cams (figure 3); some used but not excessively worn cams (figure 5); and
brand new cams (figure 6), to get a feel for the wear patterns. The "trough" at
the bottom of the teeth is visibly worn on my old cams (figure 3) and this will
be accompanied by stretch of the chain. It's very much a subjective
judgement call as to how much wear is permissible, but you should be able to
spot an imminent disaster, at least.
23. It's a good idea to take your own close up photos if possible, both for seeking
second opinions and for later comparison purposes if all looks ok this time.
24. With the inspection complete, reassembly is the reverse of strip down. If the
cover seal appears in perfect condition, it's possible to re-use it. Porsche use a
liquid sealant in addition to the moulded seal at the corners of the cover
mating face. Old cured sealant should be removed. I personally don't use any
sealant on reassembly and I have not experienced any leaks, even when re-
using the old seal.
25. Put the rags back in the spark plug recesses before refitting the cover. Check
thoroughly to ensure no tools, parts, etc. have fallen into the engine.
26. Before refitting the cover, lightly lubricate the main cover seal with clean
engine oil and make sure it is properly seated in the channel in the cover.
Take care to ensure that it does not fall out when the cover is installed. Also
make sure that the four circular black rubber sealing rings for the spark plug
recesses are in their correct position on the engine (see figure 2). When the
cover is seated properly on the engine, remove the rags from the spark plug
recesses and check to ensure that the black sealing rings are visibly in place at
the mating point halfway down each recess.
27. Check with the inspection mirror that the main cover seal appears correctly
seated all round the cover.
28. Tighten the cover screws progressively. Do not overtighten! The correct
torque figure is 10Nm/7ft.lbs.
29. Complete remaining assembly steps.