[32Hoopie]

I have now bent one pushrod and broke another. #8 cylinder first, repaired it, ran for a month, then bent one on the other side #5. Also broke a Rocker Stud. Any ideas on what might cause this type of failure? Motor has about 1k miles on it.

Specs: Chevy SB 350 .030+, TRW Pistons #L2403-030, CompCam(mild) #270H, Roller Rockers w/Guides, Stock heads - #3890462 1.94/1.5, Edelbrock EPS intake w/600 carb.

[NXS]

I would check for binding between the pushrods and guide plates first.

[BOBCRMAN@aol.com]

You are making contact in the valve train somewhere. Check the top of the valveguide/seal for contact with the inner portion of the valve retainer. Usually on the exhaust side. Check for coil bind, also common if you are using rotators and the wrong head/spring combo. Check rocker arm geometry. also clearance from rocker to stud at full lift (.060 min)

[32Hoopie]

I did check the guides and they all seem to allow the pushrod plenty of freedom. What I don't understand is how do you break a Rocker-arm stud? Actually broke 2 of them...

[NXS]

also clearance from rocker to stud at full lift (.060 min)

[sbchevfreak]

Over revving.

[evltwin]

Is your cam lift too high for the valve spring to compress? Did you use a different ratio rocker arm?

The push rod is the "fuse" to the valve system.

Check to see if your valve springs can be compressed enough. If the valve can only be depressed so far and the push rod wants to push more than somethings going to give.

[32Hoopie]

Thanks for the thought. I don't know a lot about this motor (inherited), but I do know the cam is a little bit wild and the heads are stock. I'll keep looking...

[GoneNova/406]

about two yrs ago i had a problem with using old head bolts and ended up replacing a head gasket and bought new bolts but when i put it back together i use a cheaper smaller timing chain and gear on it because i new i was going to be back in it in the very near future for something else and would use a better part then.soon i started bending 1 push rod at a time in the same aerea on the same side.i replaced them and started looking for the culprit and took the front cover off a cople of times in the valve covers constantly and soon i found it but almost by mistake.when i look behind the timing cover i didn't see the first two times that the timing chain was broke on one side(inside)but you really had to look hard to see it.i would drive it and be ok til i would get on the free way and stick my foot in it a little.or jump on it moving away from a lite.the chain never completely broke.

[32Hoopie]

That is really interesting, cuz I had talked that same scenario over with a neighbor and we kind of dismissed it as too far fetched. Getting to the timing cover on this hot rod is a real task, since I have almost no clearance between the pump and radiator, but it sounds like a worth while task. What's also odd is that the last time it broke we were just sitting at a stop light and Bam and then silence. We drive this car pretty mild so over-revving is not an issue, even at 65+ it's only turning about 2200 rpms, thanks to the 3.08s in the rear. Thanks again for the info...we keep looking...

[red eyes]

have you had any problems with the spark plug, missing a peace or bent? It kinda sounds like bad valve guide or bent valve steam. maby with the rocker arms off you can push the valve down to see if it moves freely.

[va4cqd]

look at the date of this posting. thread died in late 06

[32Hoopie]

The final diagnosis was just weak Rocker Stud Bolts. I replaced all of them with some new ARP big dogs and everything has worked like a champ.