OK, so the exhaust cam is timed by rotating it relative to its pully. This is done at the factory independently for each car because of variations in the distance between the axis of the crankshaft and the camshaft from car to car. I'm assuming that if I replace just the camshaft and maintain the original indexing of the cam to its pully, I shouldn't need to redo this adjustment using dial gauges. I'm less certain if this is the case if I replace the entire head. Anyone know if that's the case?

Thanks,
Tom

 

I assume you are talking about a twin cam head. Both the exhaust and intake cams are precision manufactured to very fine tolerances. I would speculate that the indexing adjustment on the exhaust cam is there to compensate for differences in chains linking the cams and if it is a 968 with varo-cam it would be there to set the rest position for the varo-cam chain adjuster (which is not such a precision fit to the cam housing etc).

 

Thanks Martin.

Just to clarify, it is a 968 head (twin cam, variocam).

Correct me if I'm thinking of this the wrong way, but you can't adjust the timing of the 2 cams relative to eachother, right? No matter what you do, the two cams are tied together directly through the chain and their cogs. The only way to adjust them relative to eachother would be in increments of 1 tooth on the chain. Its not a problem because of the precision with which the cams are manufactured. If this is correct, then the fine adjustment in the exhaust cam pulley only varies the timing between the crankshaft and the cams. That's why I'm wondering if it is necesary to redo the fine adjustment after replacing the head. Are the critical dimensions in the heads held to tight enough tolerances? I've never heard of anyone redoing the fine adjustment after replacing the timing belt, so I would tend to think that it would be OK.

Opinions?

 

Tom, forgive me if I am in over my head. But once the fine adjustment is done at the factory, how would changing the belt affect the adjustment. Unless the belt length or tension were different. With those variables out of picture, the belt is somewhat like the chain,(it could only be off one whole tooth) Seems to me that the ONLY way to really be sure the cam is set proper to the crank is to do the fine adjustment, when replacing the cam, pulley, or head. It does not look to be that difficult, a couple dial indicators and an air adapter to presurize the Vario Cam unit? Doug