You can buy a $900 set of heads, and a $300 set of roller rockers, and a $250 set of lifters and even a $30 set of moly pushrods....

All that doesn't make a **** bit of difference if the damn $.20 rocker stud won't stay in one piece...

The broken stud shown is the #7 cyl exhaust valve. So my question to you fellas is why did the intake pushrod bend? I'm already totally discourage so I won't be bummed if it's because the piston smoked the valve.

The intake pushrod bent, and because of that the rocker cocked off kilter and lunched the tip of the valve.

All this happend at a stoplight, while idling.

 

It sure looks like a piston smacked the valves. But since im assuming you have had that set up going for a while maybe did the timing chain break which would leave valves open. I know you said you were idling but for all its worth thats my $.02. My unlces charger did something similiar. Bent the majority of the pushrods and valves yet when we popped the heads off absolutley no piston to valve interference. We're still stumped. The only thing we can think is that they got hot and after years of use they went.

Josh

 

My '85 Z28 broke the #6 intake pushrod several years ago. I replaced the push rod and she ran strong as ever with no other problems for the rest of the time I owned her. No one could ever give me a satisfactory explanation of what might have happened (Yes, including the brain-trust here at TGO!)

 

Cap'n,

That's almost the definition of a bad day. At idle, no less. And your cam isn't even that wild.

Looks like it's time to clean out the tunnel and make room for that turbine. That blows - not as much as a turbine, but still...

ARP stud?

Did the stud appear to crack, then bend? Or did it bend, then crack? It may be hard to determine now that it's out, unless you know how it was oriented in the head. That might give you a clue as to which direction it failed. It might not even matter, since it sounds like you'll be pulling the head to see what the hell happened anyway. I was thinking that it might lend a clue as to whether the force was from the valve side or lifter side.

Do you suppose the intake bent FIRST, bumped the exhaust push rod out from under the cup in the rocker and toward the fulcrum, then the lifter slammed the exhaust open farther than was ever intended? If that were the case, I would think the exhaust push rod would have pretzeled, too. that would still indicate a valve interference problem or some other reason for the mangled intake push rod. And still. you'd hope that studs weren't the weakest link in the valve train.

I'm just hypothesizing now. This ought to be interesting. I hope the domes are intact.

 

Does this make any sense (??):

1. Exh stud broke first, so valve stayed closed. Piston (on up-stroke) builds ~ 150 psi in cyl.

2. Intake valve tries to open into high-pressure gas - press inside cyl adds about 450 lbs to normal valve opening force - intake pushrod bends?

Just some speculation, FWIW.

 

I dunno fellers. I really don't.

Vader - the studs came with the heads, I thought they were Comp Cams studs. The guide plate defnitly are because they have it stamped right on 'em. The exhaust pushrod is completely unscathed. I wonder what the chances are that the intake pushrod was bent before, then somehow that fatigued the exhaust stud?

I guess the intake valve could have gone first. I heard the POP, and then all the racket that followed. After I got it apart I assumed the POP was the stud breaking. It looks like a clean break. Doesn't really look like there were any signs of it bending.

I'm gonna pull the passenger side valve cover and see if there's any broken stuff under there.

 

The same thing happened to my buddies 289 Ford with Chevy studs & rockers on it. It ended up being that the studs were too short & the nuts would not thread on far enough, breaking off the top of the stud like in your picture.

 

Kaiser gets the prize.

The exhaust stud broke off first, right below the the nut.

Then the intake valve attempted to open against a cylinder still full of combustion pressure. That's what bent the intake push rod.

I can't tell looking at them.... are those self-aligning rockers? That would be a major malfunction, if you have both guide plates and SA rockers.

 

It's nearly impossible to tell from the photo angle, but the SA "wings" on the rockers aren't apparent after enlarging the photo - they look like 1400s.

Bending a 3/8" CrMo pushrod against only combustion pressure? At idle? I s'pose it could happen, but the Comp 948 springs have 950# of open pressure, and those are the push rods that are used with them. Once it starts to bend only a little, it's "game over" for the tube.

Also, the push rod cup of the intake rocker appears to have been impacted more than once. That IS the intake rocker on the left, correct?

And just to confuse the situation, how were the push rod lengths measured?

 

You're right Vader, I can't see the rails for sure, but I can't clearly see that they're absent either. But those are full rollers such as the 1300 series, not the roller-tip ball-fulcrum 1400s.

Those looks like the regular 7800 series Comp push rods, not the good ones.

What springs are those? Seems like it wouldn't matter too much though, that's a really mild cam.... just the same it would be worth knowing.

 

The rockers are 1301 Comp Pro Magnums. You guys already figured out that they are NOT self aligning.

The pushrods are Comp Cams pn 7808.

The valve springs are Comp Cams pn 981.

Yes the rocker on the left is/was the intake rocker. It got a little beat up, but not too bad. The bent pushrod also has a bunch of gouges in it at the top where it was jammed in the guide plate.

The pushrod length was measured with one of those telescoping pushrod measuring things.

 

There goes the "valve train geometry" theory...

Yeah, I realized that I should have said "130X" rockers. I've got "1318" on the brain for another project, and generalized about them being self-aligning.