Auto Racing: Camshaft timing, bob sharpe, dial gauge

Question
Mr. Liddy, I have asked several questions previously and received very good answers from you. I now have another question which I hope you can enlighten me. When using a dial gauge and a protractor to determine the valve full lift angle, I have been told to go for 5 degrees before and 5 degrees after maximum reading, add the two results and divide by 2. The objective is to get over the fact that dwell around the full lift point makes the precise determination of the center of the full lift point difficult to locate. Does it matter if I do it clockwise or clockwise first? In which position should I be when determining clockwise or anti clockwise, facing the water pump or facing the flywheel? TQ for your time.

Answer
I've forgotten which engine we're working upon, so the subject I raise first may be "chain lash" or "belt slop" or even "gear lash"  But in other words, looseness in the system that is driving the camshaft.

So first I would suggest you fix a degree wheel on the crankshaft and determine how many degrees of "lash" or "slop" are in the drive system before the camshaft moves.  You should be able to determine that simply by looking at it all while it rotates, and by "feel" .  Now then

With the slack ("slop" ) taken up , rotate it in the same direction you used to take up the slack,  move it the 5 degrees, and mark. Then I would go back the other direction, REMOVING the slop/slack first , by the number of degrees you recorded. proceed in the opposite direction another 5 degrees,  and make your second mark. Add the two and devide as they suggested.  This will give you a fairly good shot at an absolute zero point.  

Now, I pick up a regrind from my camshaft guy (who used to work with Bob Sharpe and Paul Newman)  and he gives me the timing card.  I install the cam according to his specs, take it to the track and find that the car runs like CRAP !  I check everything , and finally notice that at mid-range RPM there is a fog standing out above the carbs.  I'm getting reversion !!.  Reversion is from too much advance in the cam, so I end up making cam timing adjustments at the race track and of course, there I am guessing, and it's hot, and I'm mad and  sometimes it works and sometimes it doesn't.  It can also end up a little retarded, and the engine will howl at super high RPM but have no torque.  As I said, a black art.

The lesson here is that Cam timing is a science, and a really complex set of factors enter into the determination of where the cam should be. And those factors can mislead you , because cam timing is also a black art- - -like witchcraft.

So get as right as you can, and hope for the best, but without a dynamometer, your final answer is going to surface at the racetrack, adn if it doesn't , you should find someone WITH a dyno and plan on giving them some money.

I don't see that it would make any difference which direction you were to choose first.  And all references to engine rotation on all engines I know of, assume the mechanic is facing the engine from the front, ie. looking at the water pump .

Thanks for a challenging question !!

Dan Liddy
Sarasota Florida