Why are my Rocker Arms Breaking?

[72stepside4WD]

About 2 weeks ago I had a backfire (through the carb) problem that was the result of a broken rocker arm. My mechanic replaced the rocker arm and told me that he rarely sees this and thought that the rocker must have been defective. The truck ran great home from the shop and then sat for a week. 20 minutes into my next drive the same backfire noise started happening again. This time it turns out to be another broken rocker arm on a different cylinder. Both broken rocker arms happened on the same side of the engine. What could be causing this? THANKS FOR YOUR HELP!

[dan76]

Is this a recently rebuilt engine?

[72stepside4WD]

Originally Posted by dan76

Is this a recently rebuilt engine?

It was rebuilt about 4 years ago and has less the 4k miles on the rebuild. Also, it was rebuilt before I owned it. Thx.

[Ticker]

Do you have a picture of the broken arms? Seeing the failure mode will help a bunch in determining where the issues are.

Are there any marks on the stud?

Unless it's just a mechanical failure from the rocker ball galling, these almost always occur due to bad valvetrain geometry in some way.

No other changes to the engine...?

[72stepside4WD]

Originally Posted by Ticker

Do you have a picture of the broken arms? Seeing the failure mode will help a bunch in determining where the issues are.

Are there any marks on the stud?

Unless it's just a mechanical failure from the rocker ball galling, these almost always occur due to bad valvetrain geometry in some way.

No other changes to the engine...?

I did keep the original broken arm, and will upload a picture. There are no other changes to the engine.

[dwaite72lnghrn]

I would check the timing. If it were an older engine I would say the timing chain jumped on you.

[LONGHAIR]

Originally Posted by dwaite72lnghrn

I would check the timing. If it were an older engine I would say the timing chain jumped on you.

With 4k miles since a rebuild, I would doubt that, especially since he said it "ran great" on the way home from the repair. A jumped timing chain would result in seriously retarded valve timing and ignition timing, it would run really bad....if at all.


Like ticker said, Are there marks on the studs? It is possible that the cam lift is more than the rockers can handle, but that usually bends pushrods...
How about the rocker balls? Galling?
Certainly the ball was replaced on the broken rocker arm?

[cdowns]

are the heads vortecs? stock they're very limited in lift and r usually machined and speings changged for higher lifts

[PDW HOTRODS]

They might be a cheep brand. I had the same problem, I had 2 brake. After the second one, I bought a whole new set and have not broken any more. It may have taken a few miles, and a few heat cycles for them to start braking. I would still check everything else also.

[72stepside4WD]

Originally Posted by Ticker

Do you have a picture of the broken arms? Seeing the failure mode will help a bunch in determining where the issues are.

Are there any marks on the stud?

Unless it's just a mechanical failure from the rocker ball galling, these almost always occur due to bad valvetrain geometry in some way.

No other changes to the engine...?

Attached are the pictures of the Rocker Arm. It was a hairline split. I do not have the stud.

[63chevyll]

I had some speedway rocker arms do the same thing........but only at high RPM, but have never had a stock one break like that,

Were the rockers replaced at rebuild?
What oil are you running?

possibly the fulcrum balls got mixed up during rebuld??? even though i have ran many that way, maybe some of your had wear

[Ticker]

I should have said this, but the area where the rocker ball goes is the most interesting

But, if f there are no marks on the stud...then I call junk rockers. I have *never* seen a fracture like that Do you know what brand they are?

You definitely need to check the valvetrain geometery before doing anything, though. I don't like the device below much...but it will tell you if things are way off, which they'd have to be to break a good rocker.

http://www.summitracing.com/parts/PRO-66789/

These are the rocker arms I'd replace 'em with.

http://www.summitracing.com/parts/CCA-1212-16/

You're sure to hear you should go with roller tips, full rollers, 1.6 ratio, etc. Don't. Just replace the stock rockers and get back on the road.

[blwnk5]

Replace all of them i f one broke their all going to brake sooner or later the mech should have done this when the first one broke

[72stepside4WD]

Originally Posted by blwnk5

Replace all of them i f one broke their all going to brake sooner or later the mech should have done this when the first one broke

So the mechanic said that the push-rod was bent and that he sees "stress" in the other rockers. He said maybe whoever rebuilt it did not match the push-rods with the cam (he assuming they did not use a stock cam).

The mechanic said if it were his truck, he would pull out the cam to see what size it is and then replace all the rods and rockers match up. What do you think? He said, "It's not looking good."

[Ticker]

Um....no. There is no reason in the world to remove the cam, and in fact it's not possible to find the correct pushrod length that way.

If there are no witness marks on the rocker studs, then you just need to measure what length pushrods you need and order them along with a new set of rockers. Everything you need is in my post above, linked below.

http://67-72chevytrucks.com/vboard/s...8&postcount=12

You also need to check very carefully for coil bind; I suspect in the end this is what caused the failure more than the wrong length pushrod. If you look at the valve stem, is the rocker
contacting it in the middle?

Valvetrain checking springs:

http://www.summitracing.com/parts/CCA-4758-2/

Air hold fitting

http://www.summitracing.com/parts/WMR-W84005/

Valve spring compressor, on car

http://www.summitracing.com/parts/PRO-66784/

[Captainfab]

I would suggest also checking spring retainer to seal/guide clearence

[Ticker]

Originally Posted by Captainfab

I would suggest also checking spring retainer to seal/guide clearence

- basically all clearances need to be checked at this point. Normally I'd say piston/valve as well, but I guess we'll see where the rest of the stuff comes out.

[72stepside4WD]

Originally Posted by Ticker

- basically all clearances need to be checked at this point. Normally I'd say piston/valve as well, but I guess we'll see where the rest of the stuff comes out.

If I do everything above, my only concern would be that it ends up being a band-aid for a bigger problem. What are the chances there is a bigger problem, and is my only other option tearing the engine apart? Should I just see if this solves the problem?

I really appreciate everyones input!!

[Ticker]

Originally Posted by 72stepside4WD

If I do everything above, my only concern would be that it ends up being a band-aid for a bigger problem. What are the chances there is a bigger problem, and is my only other option tearing the engine apart? Should I just see if this solves the problem?

I really appreciate everyones input!!

Well, there are a couple of pieces here. If the rebuilder screwed up something so simple, then you have to wonder about the rest of the engine But the only fix for this would be to tear the thing down...and that's certainly not free. So for the shortblock you have to decide how confident you are. Nobody can give you that answer you could always at least just pull the heads to have a look....but honestly it wouldn't tell you much.

For the rocker breaking, you're going to check everything...so at least on the valvetrain geometry you'll be sure that it's right and you won't break anything else there.

If it was me, I would probably roll the dice on the shortblock and square away the rockers. Do not use this to kick my a$$ later if the thing goes up