16 bent pushrods

[Danvitt]

Hello all,

I replaced the heads on a 93 chevy 350 engine. After listening to some bad advice on how to adjust the rocker arms I believe they were over tightened.

The question here is, is it possible for the valves to be over adjusted enough to cause piston to valve contact in a stock motor?

I'm thinking no and that is impossible since the intake valve is opening as the piston is on the downward stroke. At worst I should only have 8 bent push rods. The only possible contact I can think of is the piston coming up as the exhaust valve is moving downward.

I think that the bent push rods are the result of being shoved into over compressed and binding valve springs.

What are your thoughts?

[MT-2500]

Originally Posted by Danvitt

Hello all,

I replaced the heads on a 93 chevy 350 engine. After listening to some bad advice on how to adjust the rocker arms I believe they were over tightened.

The question here is, is it possible for the valves to be over adjusted enough to cause piston to valve contact in a stock motor?

I'm thinking no and that is impossible since the intake valve is opening as the piston is on the downward stroke. At worst I should only have 8 bent push rods. The only possible contact I can think of is the piston coming up as the exhaust valve is moving downward.

I think that the bent push rods are the result of being shoved into over compressed and binding valve springs.

What are your thoughts?

I think your valves hit the piston from rockers adjusted to tight.
Exhaust valve can hit the piston to as you have found out.
Be glad the push rods bent instead of valves.
Replace push rods and do a proper valve adjustment.
Let us know how it goes.

[Danvitt]

Originally Posted by MT-2500

I think your valves hit the piston from rockers adjusted to tight.
Exhaust valve can hit the piston to as you have found out.
Be glad the push rods bent instead of valves.
Replace push rods and do a proper valve adjustment.
Let us know how it goes.

Thanks for your response. I've done some more checking and unfortunately the results confirm your suspicions. After pulling the push rods and looking at them a little more closely I actually have 8 bent push rods and 8 broken ones (their still intact but broken in 2 places).

The broken ones just so happen to be the exhaust valves. Given the angle that the pistons must have hit the valves I doubt it would be salvageable. To confirm I installed 2 straight but rusted push rods and ran a compression check on two cylinders. The number 1 spot came up to 118 and the number 3 cylinder wouldn't push past 60.

So much for me getting off easy and only having to replace the push rods. I went against my gut and listened to some bad advice to torque it down to 20 ft lbs. There was about a half inch of threads showing above the rocker arms. Which is about a quarter inch more it should have been I think. I will be counting my losses and ordering a crate engine.

[777stickman]

Hope this link will help you next time. And also the advisor!!!

http://www.classiccarauto.com/impala...t_valves.shtml

[Schurkey]

Pistons hitting intake or exhaust valves is totally dependent on piston head shape including the valve reliefs, valve size, valve timing, valve opening, etc.

BOTH VALVES ARE OPEN on overlap, and that's when the piston is at or near TDC of the exhaust stroke. If the valves are open enough--because the rocker has been cranked down too far and the valves cannot close--both intake and exhaust valves could be in the way of the piston.

"I" would compression-test and/or leakdown test EVERY CYLINDER. Even then, low compression could be from broken valve springs rather than bent valves...but bent valves are a possibility. BEST case is that the rockers are STILL too tight...

Valves would have to hit the pistons HARD to break pushrods. First Guess: Valve spring coil bind; and/or retainer-to-guide interference.

Originally Posted by Danvitt

I went against my gut and listened to some bad advice to torque it down to 20 ft lbs.

That'd be correct for certain Pontiac engines having the so-called "bottleneck" rocker studs. There's no "adjustment" per se, the nuts are torqued and lifter preload is assumed to be correct. Requires precision machining of numerous parts.