SBC -- bent pushrod -- what to do

So I was getting the car ready for the upcoming autox/de season. Pulled the valvecovers because I wanted to remove the show-n-shiney covers for the stock ones. The pics show the rest of the story. Not sure why this happened or exactly what I should do to fix it. I've asked two friends that I know what they are doing (more than I do) around engine related stuff -- one says replace the bent pushrod, ,check remainder of valvetrain for similar problems, readjust valves, check compression and move on. The other says do a total teardown/replace bearings because there has to be metal everywhere.

So the questions for the class are:

• What are possible causes?

• What are the best remedies?

• In your own opinion, is a teardown really necessary?

Engine in question is a 1991 tuned port/L98 from a Corvette. Factory roller lifters/ZZ409 cam from TPIS.

Pics:

Check the stud height and if not pulled up, replace the pushrods with the thickest wall stock diameter ones you can find.

I am not sure I would go the entire way to tearing the engine down. I would do what friend # 1 said.

As far as causes.... Hmmm.. Adjusted rocker arms without the lifter being fully extended? If that is the case, I would take the head off. Check the valves for that cylinder (I had one make slight contact with a piston and was bent BUT it still sealed). Check the top of the piston in that cylinder.

I gots nothing else.

Good luck!

Rob R.

The second pic looks like that rocker was adjusted lower than the ones surrounding it. That will cause binding/bending. I would replace that pushrod with a new one, and adjust correctly (slowly tighten until you can't spin the pushrod, turn 90*).

+1 to Bobzilla -- and this is why I come here over and over :-) Did not think to check the pics for that. You are correct -- that rocker is showing less threads on the polylock than the others!

Thanks -- keep the comments coming!!!

That wouldn't be as much of an issue on the stock cam. There's plenty of room in the springs for the stockers to be tightened even a little over. But once you bump the lift up it gets really serious. I know when I put together the 88 TPI even with new springs matched to the cam, I bent several pushrods by over tightening them just a little too much. I bent mine turning it over by hand on the engine stand.

orphancars wrote: * What are possible causes? * What are the best remedies? * In your own opinion, is a teardown really necessary?

Possible causes - improper adjustment can do it. If you have too much preload with the plunger near the bottom, it could run well for years and then one time when it is hotter than normal it runs out of lash. A good intake backfire can do it. A spring/retainer package that is close to max lift can do it. Same as the lash/heat scenario above. If you have a spring/retainer combo that hits interference at .550" lift and your cam/rocker combo gives you .540" lift, high RPM/high heat, tight lash, and bent pushrod. I've also seen just poor pushrod craftsmanship and it just decided to fail. There is another story that I can't prove or disprove. Some old-school guys swear that its possible for a spec of something to get jammed in the orifice of the lifter in effect making it a solid lifter for a second. I don't buy it, but I guess it is technically possible.

Replace all pushrods with stronger ones, or replace that one only, doesn't matter. Recheck your lift clearance. Revisit your valvespring selection. If you have stock type retainers and springs, they are heavy. Asking a stock pushrod to control them is asking a lot. Is your seat pressure too high? Often times cam manufacturers (especially with rollers) spec spring rates that are too high. They want their cam to perform well and pushrods are your problem. I would then do a good flush with a few oil changes and filters, but don't worry about it.

I certainly don't think a teardown is warranted. I suspect that if you pull the pan you might not even see flakes. But whatever is in the pan, that should tell you what needs to be done.

Broken roller lifter ?

Was that one rocker arm off the top of the valve when you opened it up? Looks to me like the pushrod guide plate has a notch worn in one side, that could have allowed the rocker to rotate to the side, which would let it pop off the pushrod, which could have bent the pushrod.

If the guide plate is worn replace it, along with the pushrod itself. Check the top of the valve stem to make sure it's not rounded off from the rocker sliding sideways, also check the face of the rocker for wear.

I had a similar thing happen to the engine in my Pontiac a few years ago.

I'd drop in a new pushrod, or even borrow one from an adjacent cylinder for a moment, see if its operating correctly, and if so, carry on and blame it on misadjustment as stated.

Curtis -- thanks -- will check springs. That is one thing I was accepting as not a problem. The ZZ409 does have more lift than the stock cam and the guy that did the heads is very good at what he does....still bears a peek "while I am in there"

You did bring up what is in the pan -- only thing I have ever found is a little metallic sludge stuck to the magnet in the drain plug. That sludge (if I can even call it that) isn't even enough to cover my pinkie fingernail and it's not gritty at all.....it's smooth. Oil always comes out honey colored in this motor. Granted I change it more often than needed (usually changing it every 6-12 months/ < 500 miles) and using a high capacity K&N filter. Might do a couple extra changes after I finish up with this little issue.

orphancars wrote: Curtis -- thanks -- will check springs. That is one thing I was accepting as not a problem. The ZZ409 does have more lift than the stock cam and the guy that did the heads is very good at what he does....still bears a peek "while I am in there" You did bring up what is in the pan -- only thing I have ever found is a little metallic sludge stuck to the magnet in the drain plug. That sludge (if I can even call it that) isn't even enough to cover my pinkie fingernail and it's not gritty at all.....it's smooth. Oil always comes out honey colored in this motor. Granted I change it more often than needed (usually changing it every 6-12 months/ < 500 miles) and using a high capacity K&N filter. Might do a couple extra changes after I finish up with this little issue.

yup. Sounds like you dodged a bullet. Replace that pushrod, check some stuff, and run it like its stolen.