Valvetrain breakage - Non-Buick

[TR Custom Parts]

Have a friend that has a 71 Chevelle with a 454 big block in it. He has broken three pushrods in the past few years on the same cylinder. A while back he had someone replace the lifters without changing the cam which I always considered a no-no. This is a moderate hydraulic cam and he has roller rockers. The pushrods are 7/16" and they are snapping off at the top. I would think it might have something to do with the cam itself, maybe a lobe rounding off and creating too much slack?? Any ideas?

 

[John Larkin]

I would suspect coil bind first. it might even be the internal dampner springs that are binding. Also since BBCs are splayed valve arrangements look at the guideplates for interference. Who knows, maybe the wrong keepers were installed on that cylinder's retainers if that is even possible.

 

[bruce]

Originally posted by BuickGn Boosted
Have a friend that has a 71 Chevelle with a 454 big block in it. He has broken three pushrods in the past few years on the same cylinder. A while back he had someone replace the lifters without changing the cam which I always considered a no-no. This is a moderate hydraulic cam and he has roller rockers. The pushrods are 7/16" and they are snapping off at the top. I would think it might have something to do with the cam itself, maybe a lobe rounding off and creating too much slack?? Any ideas?

New lifters on a used cam is fine, new cam with old lifters is a no-no, if reusing lifters with a given cam, they have to go back in the original places.

I'd look to make sure the actual geometry is correct. ie Prussian Blue the valve stem tip, and make sure the rocker is tracking on the center of the valve stem.

Then measure the lift at the rocker's tip.
Look at the rocker of contact with the retainer.
Then possible coil bind.
Then test the spring rate. A soft spring can let the valve float early.