now that i have read up the book...what if I screwed up the cam timing?

[Zendalar]

Now that I have read the Waynes book, i was just wondering that what would be the effect if I somehow screwed up the cam timing.

The engine works, but would that affect performance, would some cylinders act weird, how would it affect ignition timing etc etc..?

Whats the outcome of wrongly adjusted cam timing if the engine still works (I have driven 2500km after the rebuild)?

[Doug Zielke]

And just *what* did you do to make you think you screwed up the timing?

[Wayne 962]

Lower than normal power. If you really screwed it up, then you would have piston to valve contact the first time you turned it over. Checking the valve timing is very, very easy with the dial gauge - just remove a valve cover and install the gauge. You can probably check your timing on both cams within an hour...

-Wayne

[snowman]

Depends on how much you screwed it up. It may acutally help perfromance in some cases, but Wayne points to the worst case, ie piston valve contact.. You clearly do not have this case.. SO how do you know its wrong, and by how much????

[Zendalar]

well, it seemed too easy when i did so :9 I just wanted to know what would be the effects

[sayah]

I had the same situation with my 71T. While replacing my tensioner, the chain slipped. I didn't realize it and started the engine. I heard a Klink sound. My mechanic told me I ruined a valve. I redid the valve timming 2 more times but I the engine will not idle and has absolutly no power. Is this a timming issue or did I indeed ruin a mechanical part. When the engine is running, or if it is turnd over by hand without the plugs, the engine sounds perfect.

Any informed responses woluld be greatly appriciated.

[Wayne 962]

Run a compression check - that will tell you for sure. Odds are that you did bend a valve or two, and it's getting zero compresson on those cylinders...

-Wayne

[snowman]

I just checked how many degrees of crankshaft rotation corresponds to the normal tolerance the factory allows in setting the cam timing. It is about plus/minus one degree. In my case thats 0.090" to 0.105" valve lift with a 1970 911T. For the lower performance engines like the T and the E you can probably get by with as much as plus or minus 10 degrees without hurting anything. I have not verified this so be careful. With the higher performance engines like the S you might possibly run into a piston at 10 degrees, but my guess is that even here there is not a great risk, not sure though so be sure to check it yourself. I suspect that you would need about 20 degrees with the S to hit the piston for sure. YOu can estimate the number of degrees by assuming about 0.007" for each degree. Only good for small number of degrees.

What is the effect of advancing or retarding the cam by 10 degrees? It will not be extreemly noticeable but you will get somewhat better low end performance with a cam that is advanced and somewhat better high end performance with a cam that is retarded. If you have over camed an engine and you hate having to run it up to 1500 RPM just to get it started you might solve the problem by advancing the cam. This would make the car act more like a normal car, but would give up some of the highe end go power. If you like hearing your engine sing and want more high end and do not care about getting off the line your might benefit by retarding the cam. My personal experience is that 5 degrees is not enough for the normal driver to notice much, ie only the most pickey will be able to tell the difference. 10 degrees will make a difference a normal person can readilly notice. More than that you have the wrong cam and need to change it.