Cam Diag

[Kidd-7]

I have a 71 C-10 307 3 on tree. I have been researching the 307 and read somewhere that the cam was a problem in this motor; wearing out prematurely. My question: How do you diag a worn cam?

[geezer#99]

Pull the valve covers and watch the rockers for how much they move. Flat lobes will be easy to see. You don't need to run it. Just get someone to crank it over for you. Less messy that way.

[Kidd-7]

Originally Posted by geezer#99

Pull the valve covers and watch the rockers for how much they move. Flat lobes will be easy to see. You don't need to run it. Just get someone to crank it over for you. Less messy that way.

Kinda figured that; it makes sense. Whats the chance of all of the lobes being worn the same or close to the same?

[geezer#99]

I've never seen more than a couple worn at a time.

[RIA69]

for what its worth I my '69 had a 307 in it that had four (4) flat lobes. all this I found out after I was 3/4 of my way through a 1200 mile trip to KS. it was making an awful noise like very bad back firing. the way I was able to finally find it out was like stated above pulling the covers and turn the engine over.

[screamin_c10]

Remember, barring catastrophic failure, the lobes don't just go round. They wear down over time and will still remain somewhat egg shaped.

With that being said the lifter will still move up and down in its bore and the rocker will still actuate the valve, just not as much as the valve-train on a healthy lobe. So even if you don't see anything as obvious as a rocker just sitting there motionless you could still have heavily worn lobes.

I would rent a dial indicator and check the travel of the rocker / valve on any suspected worn lobes.

Below is a pic of the cam I just pulled from a very good running 307 and it is very clear the lobes circled are very worn, but not round enough to stop valve actuation....The truck ran and idled perfectly at ~ 750 RPMs