Porsche 968 - ASSEMBLY INSPECTION PROCEDURE AND MAINTENANCE SCHEDULE Maintenance Manual page 7

30. Reset clock and radio codes if necessary! (due to disconnected battery)
31. Drive and enjoy! (hopefully.........!)
Suggested Variocam Wear Limits
As stated above, we are in a very subjective evaluation territory here, and there is no
official data on which to rely available from Porsche. Moreover, the "wear limits"
can be precisely checked only by dismounting the Variocam itself, and at this point
you have done all the work, and you can substitute all the worn parts without
significant extra work.
From the observed Variocam failures, it appears that a chain stretching of 4mm
coupled with a pad wear of 2mm in at least one of the pads, is enough to produce
serious and irreversible wear on the cam sprockets (particularly the intake one),
ultimately leading to total Variocam (and potentially engine) failure.
We assume here that a safe "wear limit" is to stay within 50% of such observed
"fatal" limits. In conclusion:
Item Wear limit
Tensioner pads 1 mm (max deepness of tracks in the nylon pads)
Camshaft chain 2mm (half stretching of the closed chain, corresponds to 4mm
of stretching of an "open" chain)
As observed before, the pad wear can be asymmetric, and sometimes the lower
hidden pad wears more than the upper visible one: as suggested in the inspection
procedure, use a small mirror to carefully inspect it as much as the limited access
allows. Any signs of cracking, more probable at pad corners, means the pads need to
be changed. Pay attention to signs of age, leading to brittle pads more prone to future
cracking: the age is denoted by:
• Dark brown color of pads (new ones are light brown). This is not a definitive
criterion, but comparing fig. 4, 5, 6 you can see that the darker pad is the worst
one;
• Small "craters" visible in the wear grooves. These craters means the nylon is
brittle, and small chunks of material are thrown away in stress conditions. 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. A
macroscopic difference of 3-4 mm should be detectable even by surrounding the
installed chain with a thin flexible inextensible wire (eg steel or inox wire) and
comparing the "ring length" with same measure on the new chain. I did not try this
method, but should work.
The effects of a stretched chain, are easily visible on sprocket wear patterns. Figure
5 shows a used but "serviceable" camshaft, while Fig. 3 shows a badly damaged