Finally some Cam Degree Numbers - Now what?

JSeery said:
He checked that the mark on the cam gear lined up with the mark on the crank gear. The current question is if the cam gear is mismarked.
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Cut and paste tells me he checked that


"After comparing the cam gear with another, matching bolt patterns and matching marks. I left the cam and crank gears in place. The cam itself has been run in another motor so I was convinced the cam itself is a good 77B."
 
Just some numbers to ponder: His readings show the exhaust closing at 9 ATDC - with .014 lash. The cam card specifies 19 degrees ATDC - with zero lash. So you can assume that with zero lash, it will close LATER than 9 degrees . . . probably a couple more.

So, with some guesstimating, maybe 11 - 12 degrees afterwards. So, that means you need about 8 more crankshaft degrees (retarded) to get it to 19 . . . hence my thinking that he'll need a "tweener". From his original numbers, I doubt a whole tooth will get him where the cam card says it should be.

To backup a bit, we don't know WHAT mechanical problem is causing his issue - could be the crank gear, could be the cam gear, could be how the cam was ground, advance issue (timing) can also be related to the cam slot location . . . or a combination of all of these.

To me, one has to pull the heads, zero the lash, get a dial indicator, use a mag base and a good degree wheel - and start from there. Only then will he be able to truly figure out the accurate "as is" cam timing - then you go from there.

I'd do this before undertaking any sort of "fix". With that said, one can do the "catch me screw me" method of just trying stuff - but I've never found that to be terribly successful and also one never truly knows what the root cause was in the first place.

Best of luck!
B&S
 
I appreciate the lesson in cam checking, but as the process has unfolded, I don't understand why more attention wasn't paid to the fact this cam ran fine in an earlier installation. It simply came down to "what caused the static timing to be so advanced. It wasn't the cam, demonstrated by prior use, but the cam was off time. The cam gear was the only component with which I had no prior use experience.

I generated the numbers requested for the cam which were actually quite relevant and helpfull, as both Int and Exh had the same lobe center, so a decent set of exhaust numbers said a lot. I am happy I did not succumb to pulling the heads again as it made no sense to do so with the info that was obtainable from the exhaust valve, and the cam history.

I did learn a lot from you guys, and I thank you for your time analyzing what info I was able to provide. Special thanks to "flatjack9" for coming up with the solution to the problem. His recommendation to retard the cam one tooth brought the timing right down to where it is supposed to be. The timing gear was miss-marked. I pulled the cam gear, advanced the crank one tooth, put the gear back on and walla, timing perfect. It runs great too.

I must add. I have become a believer in the wisdom of checking a cam early in a build.
 
I enjoyed following along on your ordeal, glad to hear you were able to resolve the cam timing issue. I better buy a degree wheel.
 
Russ/40 said:
I appreciate the lesson in cam checking, but as the process has unfolded, I don't understand why more attention wasn't paid to the fact this cam ran fine in an earlier installation. It simply came down to "what caused the static timing to be so advanced. It wasn't the cam, demonstrated by prior use, but the cam was off time. The cam gear was the only component with which I had no prior use experience.

I generated the numbers requested for the cam which were actually quite relevant and helpfull, as both Int and Exh had the same lobe center, so a decent set of exhaust numbers said a lot. I am happy I did not succumb to pulling the heads again as it made no sense to do so with the info that was obtainable from the exhaust valve, and the cam history.

I did learn a lot from you guys, and I thank you for your time analyzing what info I was able to provide. Special thanks to "flatjack9" for coming up with the solution to the problem. His recommendation to retard the cam one tooth brought the timing right down to where it is supposed to be. The timing gear was miss-marked. I pulled the cam gear, advanced the crank one tooth, put the gear back on and walla, timing perfect. It runs great too.

I must add. I have become a believer in the wisdom of checking a cam early in a build.
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Way to go Russ!!!
 
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