3.0 cam timing help needed
 

I have an 80 3.0, and I am finishing up a top end rebuild, the following are questions on cam timing:

First, the book mentions prying the tentioners to relieve pressure on the sprockets. What is the intention of this step?

Then the books says to move both cams until the punch mark on both sides is up? What punch mark? On my cams there are two marks, one looks like a part number, the other looks like a stamped "930". I ended up installing each cam with the crank up at the Z1 mark where I was assuming 1 and 4 were at TDC, so each cam was rotated to have both 1 and 4 valves fully closed. The left cam ended with part number up and the rights cam ended up with the "930" up were the crankshaft was up at the Z1 mark. Is this correct ?

I turned the crankshaft to set TDC on various cylinders and adjusted the valves on the left bank, (1,2,3) to .004 in. at top dead center for the appropriate cylinder. When I turn the crankshaft, nothing on the left side binds, but at times the exhaust valves when not at TDC have more play then at TDC, .004 in. Is this correct?

I know how important the cam timing is and want to be sure and do it right. What can I check to 100% verify the timing is correct?

Do you have the factory 'spec book' and Bruce Anderson's 'Porsche 911 Performance Handbook' ??? He has a discussion on the the various timing settings for an SC. If you have (or can borrow) a dial indicator and magnetic base, you can check the timing at TDC overlap as given in in the spec book, for cylinders 1 and 4. That guaratees the timing is correct, or within spec for both sides of the engine.

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Warren Hall
1973 911S Targa

I have Bruce's book, along with a good dial indicator. I am just a little "Junior" at this. When you say "Overlap", do you mean simple valve clearence?

No, overlap acually refers to that portion of the timing curve where both exhaust valve and intake valve are both 'slightly' open. It is actually one crankshaft revolution before the ignition firing point.

My mistake referring to a magnetic holder, that can be used for checking the timing when the engine is mounted in the car ... when you are still putting the engine together, there probably no sheet metal attached to the engine, and you need a 'Z' holder. What you are measuring when checking the cam timing is the actual amount of lift at the valve ... how far off the seaty the valve has been pushed down by the rocker arm. That value measured precisely determines how far up the ramp of the lift curve the cam is at.

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Warren Hall
1973 911S Targa

OK, after re-reading Anderson's and Hayes several times, I get it. I have measured the overlap to be exactly .059 in., which is within valid range for an 80 SC, (.055 to .067).

Thanks for the input...