cam questions

[Ryan Wright]

my dad has a 1976 corvette, because it was backfiring when you would try revving it up around 3k rpms, we were told it could be carb, timing, and now cam, The carb was just rebuilt, so i doubt that, and the guy saying cam has been wanting us to do a top end rebuild for a while.

we were wondering how to check a cam on your own, and possibly a good but lower priced corvette mechanic in broward/ palm beach counties in florida

[Jim38243]

Re: cam questions

You could do a visual inspection by removing the valve covers, remove the rocker arms then pull out the pushrod and lifter. Look carefully at the bottom of the lifter for wear or scratches and be certain you put the same lifter and rod back in the hole it came out of. If you can see wear odds are the cam is badley worn and should be replaced. Before I did this though I would be certain your timing is set properly and your distributor functions correctly. Good luck!

[Clem Z.]

Re: cam questions

the easy check is to bump the engine over and check the lift of each valve at the spring with a machinest ruler. you can not check the lifter with out removing the intake manifold. if the lobe is worn enought to cause your problem the lost of lift will be easy to spot.

[Doug Flaten]

Re: cam questions

Maybe I am wrong, but couldn't you also be chasing a vacuum leak or lean condition at the higher rpm's? You may have a warped carb base, leaks on vacuum lines or the intake manifold. Carb rebuild kits do not typically have throttle shaft bushings, and you could have a leak entering via the throttle shaft.

[Duke W.]

Re: cam questions

I reommend going down the vacuum leak path before you remove the valve covers for a valve lift check. Think of all those 25+ year old vacuum hoses and Corvettes have a lot of them (don't forget the headlight actuation system).

A vacuum leak will cause a lean condition, which is usually the cause of backfiring through the inlet system, which should not be confused with afterfiring - popping in the exhaust. Under load this can be caused by a leaky valve that allows unburned mixture into the exhaust system, which then ignites after it's heated to the autoignition temperature.

Duke