Timing 4-strokes

[Debra]

This note is in response to Clarence Lee's recent engine clinic column
on timing 4 stroke engines.

I always recheck my cam timing in 4 stroke automotive engines by a
simple method. Set the crank at tdc of the exhaust stroke on #1
cylinder. Slowly back off both valve clearance adjusters until you can
get a .005 feeler gauge in. Then rotate the crank to the top of the
compression stroke. Recheck the valve clearance. It will be quite a
bit largeer, but both valves should be within +/- .005 relative to each
other. If the cam is off one tooth, it will be obvious since the
clearances will be quite different.

I learned this from Iskenderian many years ago and it is based on the
assumption that the cam(s) are designed with "split overlap". Most of
our cams are indeed designed this way.

Cheers,

Mike F

Dear Mr. F --
Thanks for the info regarding Ed Iskendarian's method of checking valve timing. This is a new one on me and I have installed and degreed many automotive cams over the years. I don't think it would work on some of the cams that are installed one or two degrees advanced or retarded. I gave it
a try on both a Saito 91 and O.S. 120 without much success. A small movement of the crank one way or the other makes a big difference in the valve lift, in turn making checking the valve clearance pretty difficult, not to mention trying to keep the pushrods from falling out of their sockets. I think just bringing the piston to TDC on the over lap stroke and noting whether both valves are the same is a lot simpler.

Thanks again for taking the time and having the interest.

Regards,

Clarence Lee