Got the L98 running, but the #3 cylinder can't keep pushrods. It'll run for a few minutes then make a tapping sound. I pulled the valve covers off yesterday and both pushrods were inside the lifter valley. I put two new ones in and re-adjusted all of the valves and the same thing happened again. What would cause this? I don't want to keep feeding it pushrods.

 

Maybe a bad lifter/sticking valve? Is the rocker and spring in good condition? I really can't say tough, I'm not very keen when it comes to the valvetrain.

 

You running aftermarket intake manifold bolts? If these are too long, the bolt will contact the pushrod on certain cylinders and cause failure.

 

stock bolts

 

Have you verified the lengths though?
I've seen some of the stock outer intake
bolts that are longer than the inners..

Do you have screw-in rocker studs, or
press in? Any chance the press in studs
worked up?

Any engine work done? Any chance the
piston may be hitting the valve, or something
broken off in the cyl that is contacting between
the piston and valve?

Slotted rockers hitting the slot with a high-lift cam?

that's all I could brain dump at the moment..

mike

 

hey thanx man. I didn't check the lengths before I took them out. I think they're all the same though. I'm in the middle of pulling the head off now to see if anything made its way into the cylinder. It's all I can think of and the intake was already off, so what the hell is another hours worth of work ya know? They're screw in studs with stock rockers and a ZZ4 cam. I don't think I'm hitting the end of the slot otherwise it would happen to all of the cylinders. There has to be something in the cylinder. Thanx for the input, I'll keep you updated.

:lala: :lala: :lala: :lala: :lala: :lala:

 

The guide holes in the head may not be big enough on the particular cylinder and that's what's bending the pushrods. I've seen it happen in the past.

 

Guide holes? I guess you mean pushrod guide holes? They look like they'd be plenty big. It's a huge opening. They're L98 Vette heads.

 

Hopefully it's not, but worse case scenario is that you're flattening out the cam lobe on that cylinder. It could have worn down to the point that there was excessive clearance. Then when you installed the new set, it wore down even more causing again excessive clearance. Something you might want to check.

 

I'd say check your lifters! Matt

 

I had same problem in a 454. Kept eating #6. Found out that one of the lifters was junk. (Probably because I had the engine temp up to 260 at one time) I replaced 2 pushrods before I decided to go with new lifters... Runs great now...

 

Sweet. Thanx guys. The head is coming off tonight. I figure why not, I'm already halfway there. If I don't find anything I'll try new lifters.

 

If your using the vette heads, I believe that they require the use of guide plates and non-self aligning rockers.

 

whats the reason for that? they're almost identical to lt-1 heads

 

Nah. Mine came from GM with no guideplates and instructions to use SA rockers.

 

are you using the locking nuts (nuts looked squeezed on top) and not regular nuts.... best of luck, tom

 

Pulled the head off while crossing my fingers and I got lucky. There was nothing in the cylinder. Now I have no Idea what could be causing it. I'm going to take it to the machine shop that did the work on the heads to be checked out. The only thing that I can think of is that they didn't cut the valve guides down enough on that cylinder and the valve lock is hitting the valve seal causing everything to bind up and the pushrod is the weak point. It's a long shot, but it's all that I can think of. Thanx.