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Setting the Camshaft Timing
The Porsche 968 Workshop Manual describes setting the camshaft
timing in section 15. Perhaps something was lost in the translation from
German to English but having recently performed the procedure I found
the manual wording a little short on detail and a tad confusing. But after
consulting various Porsche experts, doing some deep thinking and re-reading
the manual a few times, finally it all fell into place.
The Porsche 968 Workshop Manual referenced here is the 1991 version, section 15.
Following is how I reckon the paragraphs on pages 15-3 through
15-6 should be worded (note I have not checked this lines up with later
Regarding engine rotation:- When standing at front of the car looking at the front of a engine the normal direction of rotation is clockwise. To rotate the engine I used a 24mm socket on the crankshaft pulley at the front of the engine, so from here on if I say rotate engine forwards or clockwise I mean clockwise from this perspective.
1. Rotate the engine in forward
direction until the piston / cylinder #1 is at firing Top Dead Centre
2. Mount two dial gauges on the cylinder head. Dial gauge #1 requires a straight extension of approx. 200 – 210 mm length to pass right through the spark plug hole onto the top of piston #1. This is used to determine when piston #1 is precisely at TDC. Dial gauge #2 requires a bent extension to touch the top of the hydraulic tappet / lifter for cylinder #1 inlet valve. This gauge must be mounted so the vertical movement of the dial gauge is in line with the inlet valve stem axis. Pre-load dial gauge #2 by approx. 3mm.
The manual recommends mounting using “VW 387” dial gauge mounts. If these are not available, as an alternative approach: Dial gauges often come with magnetic mount brackets. I found it easy to bolt some scrap metal brackets onto the aluminium heads, thus providing solid platforms for the magnets to do their thing and hold the dial gauges firm and steady.
3. Remove the three screws & spacers holding the distributor rotor. Leave the rotor off, and fit three temporary screws M5 x 15 to bind the camshaft gear back onto the backing plate behind it.
After this whole process is done and the drive gear has
been clamped onto the camshaft (by the large
This is achieved when, with Variocam pressurised, the depression
of inlet valve of cylinder #1, relative to it’s relaxed position,
must be in the range 0.36 to 0.42 mm (0.39 +/- 0.3mm) when the piston
is precisely at non-firing TDC.
4. Undo the M10 bolt in centre of the camshaft drive gear, simultaneously using a counter spanner to keep the camshaft from rotating. Also loosen the three temporary M5 bolts. Rotate the engine backwards (anti-clockwise) a short distance, until the woodruff key in the camshaft meets the end of the keyway slot in the camshaft drive gear. See figure a bottom right of page 15-5.
5. Tighten the temporary M5 bolts to 6Nm (4 ft lb) and the central M10 bolt to 40Nm (29 ft lb). The timing adjustment is now fully to one end of the adjustment range. The engine is still near cylinder #1 firing TDC, point (A) in the Timing Chart.
6. Remove the oil feed line from the top of the Variocam unit. Using a special adaptor (tool 9529 or similar) as shown in figure 799-15 at the top left of page 15-6, feed pressurised air into the Variocam at a constant 3 bar approx. (44 psi). This simulates the oil pressure that is present when the engine is running.
7. The engine is still near point (A) in the timing chart. Using dial gauge #1 and small rotation movements of the engine locate cylinder #1 at precisely firing TDC.
8. Zero the reading on dial gauge #2 (the inlet tappet).
9. Turn the engine one full
rotation in normal direction (360o clockwise) until Cylinder #1 is near
nonfiring TDC, point (B) in timing chart. As you rotate the engine and
approach point (B) the inlet valve on cylinder #1 will start to open.
Rotate until dial gauge #2 reads between 0.36 and 0.42mm.
10. Carefully undo the M10 bolt at centre of camshaft drive gear, ensuring the camshaft doesn’t rotate and the reading on dial gauge #2 stays steady in range. Now the camshaft is effectively disconnected from the crankshaft, we are ready to do the fine adjustment of the engine timing.
11. Slowly rotate the engine until dial gauge #1 indicates the engine is precisely at TDC. The camshaft lobes for cylinder #4 should appear as in figure 800-15 at the top right of page 15-6, and the flywheel mark should also align again as shown in figure 796-15.
12. Tighten the temporary M5 bolts to 6Nm (4 ft lb) and the central M10 bolt to 65-70Nm (48-52 ft lb).
13. Your engine timing is probably done now, but to be sure rotate the engine forward through two complete revolutions and check the settings again.
--- Congratulations, your Porsche 968 camshafts are now timed to the factory specification ---
Thanks go to Chris Jennings(Sparky) for this valuable addition to our technical section.
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