[notmytarga]

I made my umpteenth trip to the garage to set the L cam timing as I reassemble my rebuild. I'm working with the stock cam on my 1975 911S so I used several references to verify 0.4-0.54 mm of overlap. (Wouldn't a typo here be horrible??) This worked out to 0.0185 +/- 0.0028 inches on my non-metric dial indicator. I have them set to 0.0179 and 0.0178 finally. Slightly 'retarded' but matching at midrange.

I found that the indexing pin does little to fix the timing at a desired point. It DOES fix it to a range - one that matches the spec books. I was curious whether the various pin/sprocket/toothed sprocket flange rotations would have varying amounts of play. I measured all the combinations, used an Excel graph to find a smooth increase in the size of the range as the rocker rode the cam further up. So I believe my parts are not worn out. Then again, the pin could be the culprit it I'm wrong on this range thing. It fits tightly and doesn't look worn. Do new parts have this range??

As many have described in other threads, cranking down with the 46 mm crowfoot will change the setting. Inevitably. Everytime. With only variable consistency.

In case you haven't spent hours thinking about this, here is what I figured out. If the pin only holds the timing in a range, then the spot-on timing you desire is dependent on the position and friction between the sprocket flange (indexed to cam tightly with woodruff key) and the chain sprocket. Torquing the nut while holding the cam only indirectly stabilizes this connection. What would be best is to have a way to hold the sprocket while tightening the nut. Oh wait - that is what the updated cams use! Lucky them.

Others have recommended locking the flywheel and using the crank/Int shaft/chain to hold the sprocket. This is a lot better at getting the sprocket to not move as you tighten but at 110 flt lbs applied to a 1.75 inch lever arm that gets you 750 lbs of tension on the chain which I would avoid.

I followed the advice given in other threads to lubricate the camshaft threads and washer surfaces with oil. Make sure the washer is within the depression in the sprocket. Tighten the nut as much as you comfortably can keeping a setting at a known value. NOW - rotate the crank so that the cam holding tool is held by the case somewhere and then concentrate on safely getting 110 ft lbs on the cam nut. Once you have the nut tight, bring the engine around and see how you did. Stop and check your zero. Which way did it drift (it will always want to go one way) and by how much? - this is the "cam nut drift" referenced ......only here. If it was right on your final target you did it wrong and you need more practice. Back the nut off and set yourself up again taking into account the "cam nut drift". Tighten up the nut just as firmly as before and then lock the tool against the case and go to 110 ft lbs again. Ideally you should make stepwise progress towards your goal of the timing range midpoint or what you eventually decide is close enough.

Of note is that I think it would be a mistake to set the pin where your intended timing value is at the end of and not the middle of the range. This may stop it from drifting as you tighten, but if the setting drifts during engine operation it could drift out of the range. I'm curious how well the friction interface really holds these values. I'll be checking my timing with every valve adjustment.

Another observation - when setting my chain alignment I measured my 8 shims at 0.5 mm rather than 0.25 mm. This allowed me to get to the other side of the 0.25 mm tolerance but not spot on. I also found that the thrust washers had slightly different thicknesses at 2.9 and 3.0 mm. I was able to swap them for better measurements.