Broken/Bent pushrods

[Immaterial]

A while ago I overheated my engine, 2.8L V6 in an '86 Cherokee. The engine was making knocking sounds, so we took it apart, figuring the heads were warped, and sent them into to be milled. They were milled, and now we're putting eveything back together. While tightening the rocker arm studs, we noticed that one of the pushrods began to bend. We immediately loosened the corresponding stud, and removed the bent pushrod. After checking it, the only real difference between it, and all the other pushrods was that the lifter was in the 'up' position for that rod. So, we 'bumped' the engine (As my dad calls it) : We turned the key for a split second to I guess change the cam positions, and try and get the lifter to go down so we could install the pushrod without it bending. The lifter went down no problem, and we installed the pushrod there and it was fine. Upon looking up, however, we saw that two other lifters had raised, and there were two more broken pushrods with them.

We need help trying to figure out why the pushrods are breaking when the lifters rise. Were the pushrods simply damaged when the engine overheated, causing them to weaken (So they can't take the pressure, and just break)? Or did the milling on the heads mean that we have to use shorter pushrods now?

[Edit: had to fix some spelling issues, heh]

Thanks for your help!

[AlohaBra]

The lifters are hydraulic and could be damaged (??).

Take them all out and take the clip out and clean them and check the fit of the internal mechanism. If they won't go down, replace the damaged lifters.

[fredjacksonsan]

Don't even try to run your engine with bent lifters. Replace them.

[Scrapper]

role them all on a board and see if any more is bent..or you can role them on any thing flat surfaced...good luck..

[Immaterial]

Well, I took out the lifters and compared them to a new one we bought, and they all look fine. They all push in about the same length, and none of 'em are bent or anything. If the lifters are OK, what should I check next?

[AlohaBra]

Put the push rods in one by one. Make sure they are straight.

[Immaterial]

I checked the pushrods. I replaced the ones that were bent with new ones. When I tried to put one of the new ones in, it bent as I was tightening the rocker arm stud. I wasn't torquing it down when it bent.

[AlohaBra]

Back to the lifter...the hydraulic part is supposed to "collapse"....about a quarter turn..

Put the rockers on... on the low part of the camshaft...till you get zero lash...then start the engine...

***I would set it for zero lash and run the rocker nut down a 1/4 turn or so with the engine running...