Problems In Big Block Land?? Help

[6600DURAMAX]

WOW, let me make this as short as possible. Put the big block on the test stand and everything seemed fine, dropped in truck and had a horrible miss/pop went thru everything and finally had to pull the cam and found a flat lobe. Installed a new 292 cam and lifters and had a valve job with new springs installed on the heads. Seemed to run fine, Lots and Lots of power but the valves were starting to tick. Sooooo now to the problem

Went to adjust the valves real quick and found a brok in half pushrod and a hole in the rocker on #5 cylinder.

What causes a pushrod to break, I am almost certain the rocker was not to tight????

Do I just buy a set of roller rockers and a new pushrod and go on with life or is there something I need to check????

Oh ya by the way I cannot find the other half of the pushrod, hopefully just in the valley somewhere I can fish it out

Any Help guys??????

[JBstor]

Well, unless there is something real weird going on, there are only two reasons.

1) stuck valve

2) piston hit valve

I have only seen bent, not broken pushrods, but I have seen rockers break under normal driving conditions.

For one reason or another (above) the rod pushed up, and the rocker did not want to move, causing the damage you describe.

At the very least, I would pull the intake to get that pushrod part out if you can, and turn the crank to check the lifters have no damage and are all working

I had a F@rd 460 bend and pop out pushrods because the intake was sucking exaust in, gummed up the valves, and jammed them. There is next to no room for give when there is a problem.

Check everything now, or fix everything later

HTH
JB

[6600DURAMAX]

I must be really unlucky then, cause the 355 that I had in the truck also broke one pushrod and bent another. Never found the cause just went the cheap route and stuck new pushrods in and ran it, never had a problem

This motor is a little different, it is an older motor but is very tight, raps to 5600 very fast with no problem (that is were the rev limiter is) and makes all kinds of power. I sure would hate to srew something major up here by going the cheap route.

Just had a buddy do a quick vavle job while I had the heads off for the cam install and installed new springs

The motor has flat top pistons and if I didn't break a valve spring I do not see how the valve could have hit the piston??

But I am not an expert by any means so any suggestions are welcome

[JBstor]

This is usually the part where things get squirrely.

Did your buddy replace the guides? Did he just lap the valves and throw in new seals? You know where I am going with this.

Also, which lobe was worn off the old cam? Was it the same lobe that you now have a broken pushrod?

Sorry, I have seen guys do a "valve job" and hammer the valves in, because they mixed them up in a bucket when they were cleaning the parts, and then expect the engine to run like a dream.

It might not be something your buddy did, or knows about, or even touched, but if it was me, the whole mess would get looked at REAL close.

JB

[Green Machine]

Check the length of the rocker arm slot. I had a big block once, that after I changd to a bigger cam, rocker arm was binding on stud at max lift and was breaking off rocker studs. Good thing they were screw in studs. Put long slot rockers on and fixed the problem.

[6600DURAMAX]

Sorry JBstor, I guess I am not following. All he did was take a stone and grind out the seat until the valve was fully seated, install new valve seals and put the new springs on. Yes the valves were NOT put back in the "original" hole. Everything went back together smoothly.

No the lobe was wore off the #6 cylinder on the original cam.

[dwaite72lnghrn]

A 292 cam is a big cam! Did you check the lift and the spring compression? If the lift is too much you should mill out the spring area to give you enough room for the lift.
I have seen bent push rods(8 to be exact, When the timming chain went) but never a broken one. maybe it came off the rocker and got caught between the rocker and head and thats what broke it. just guessing.
Also make sure the valve moves freely up and down before you put it back together.

[mr402]

I've encountered broken rockers a few times now. The flat lobe on the cam is also a big hint. When the lobe flattens the pushrod is no longer tight on the rocker arm. It will just bang against it. I still have a rocker where the push rod broke through the rocker and stuck itself in there. Rockers will also have a tendencey to split on the sides once they've worn a bit.
When you pulled the cam did you put in new lifters?
Also did you make certain to keep the pushrods matched to the port it was removed from?
Actually all that is moot at this point.
My advice is to check all the rockers for wear at the inside surface. If the surface where the ball mates to the rocker isn't smooth or looks thin replace the rockers. Check all the pushrods for straightness. Best way is to roll them on flat glass and look for any wobble. Also check the ends for wear.
Depending on where the pushrod broke my guess is that's the one that was mated to the flat lobe on the cam.

[JBstor]

See, this why I said this is where things get squirrily. It's hard to know which way things were done. I'm not trying to be confusing here, its just that there are so many ways for the thing to mess up, it's risky to leave anything to chance.

What I meant by replacing the guides, is the tubes that the valves run in. Lapping the valves is a method to regain seal on the valves if they don't require a full grind, and if they have been ground, you should lap them. It's just spinning them by hand with a plunger while they have a gritty compound on the valve/seat mating surface. It shows you how good the seal is,too.

Mixing the valves and replacing them, as well as lifters, pushrods, and rockers, is generally to be avoided. It will still run, but you increase the wear rate and chance of failure of the part, especially with lifters on cam lobes.

Anyhow, I after re reading your post again, I would also agree that the damage to the pushrod and rocker could have been from before. I had assumed that you hadn't mixed the parts.

What to do now? If the valves all went in nice and easy, check, check and double check everything you can, (Springs, lifters, rods, rockers,etc) replace the damaged parts, and give it another try. Good Luck!

HTH
JB

[Big Block]

I bought a 1970 Kingswood chevy wagon with 454ci. It ran poorly with a miss. Pulled valve cover and found one of the push rods missing. Put a used push rod in and adjusted valves. Engine ran fine. Later after I removed engine. (The car was purchased for the engine only.) I took it apart found the push rod in two peices in the lifter valley. The motor was a 4 bolt main B.B. with steel crank. Big Blocks are hard on stock pressed steel rocker arms when they are used with high lift cams. I would invest in a good set of aftermarket high performance rocker arms. Good luck. B.B.