Team Chevelle banner

Broken rocker arm, replace one or all?

20K views 20 replies 11 participants last post by  MikeC66 
#1 ·
Hi all, was out the other day for a drive and heard pinging under the hood, so I shut it down immediately and got towed home. A look under the valve covers revealed a broken rocker arm (cyl 5) split in half at the stud. Since then, I have looked at a ton of articles and posts about possible causes, etc., especially since the engine has run smoothly for first 10 thousand miles. I think it is likely that the original rocker arms were reused when the engine was rebuilt. So I am hoping that the failure is due simply to age/fatigue rather than some of the more serious things I have read about.
My question is should I replace only the broken arm, or all of them? Based on a visual inspection, I don't see signs of stress in any of the others. But I have a new complete set if I need it. Also, should I replace the push rod(s) as well? Also, most of what I have seen relates to roller arms, and I was wondering if anyone knows of a good reference post/article on setting lash on stock/solid rockers?
Engine is stock 350.
Thanks so much!
Mike
 
#2 ·
I would change them all as well pushrods , just for the peace-of-mind. This may have been a fluke but it will worry you about a repeat failure. Put a little moly grease on moving surfaces. Get some oil stopper clips or cut the middle out of an old stock valve cover. Engine needs to be near operating temp for final adjustment. Get as close as you can when replacing old rockers, crank it and adjust all the noise out.Once its running smooth , loosen each until it clicks ,tighten slowly up to a full turn-I like at least 1/4-1/2 turn but each engine seems to respond differently. It will be messy so I would do one side at a time-leave the cover bolted down to minimize oil leakage .
Things get hot so it may take 2 runs to get both sides done-after a cool down
 
#5 ·
Thanks for all of the replies!
I guess the one unknown is how old they really are (assuming the engine builder used the originals, which may not even be from this engine).
I wonder if an arm fails all at once, or might there have been some signs of fatigue I could have seen (had I looked).
I also wonder why this arm in particular broke...perhaps just luck of the draw.
Mike
 
#6 ·
I took some time to more carefully inspect the other rocker arms and I see another one that looks a little suspect. It has what appears to be a tiny hairline crack developing at the push rod pocket. So I am thinking of replacing all of the arms.
Before I start, I have a couple of additional questions:
I compared the new arms I got (GM replacements) and they are identical to whats on there now, except that the valve end has small shoulders (not sure what to call them) that appear to center the valve on the arm. Whereas the old ones do not. Is that okay?
Also, some of the old arms seem to have a lot of play when you wiggle them by hand (but zero lash of the push rod). Since I have not done this before, I am wondering if that is okay.
Thanks again for all of the help!
Mike
 
#8 ·
I rebuilt a old 307, bored, turned crank, valve job, bigger cam etc. I reused the rocker arms and after the rebuild and many many thousand miles I had a rocker break. I swapped it out with another used rocker, and a few weeks later a different one broke and a few weeks later another one. Probably should have just replaced them all, but I was cheap and lazy. Jim
 
#9 ·
Believe it or not, Chevy's have been known to eat rockers. I've seen them push through the pushrod pocket, Iv'e seen them break at the fulcrom point. Change them all, stock rockers your out not alot of cash. Valve covers are off already. Check pushrods, make sure they are not worn to an irregular shape from a worn pocket.
 
#11 ·
Good read, had to read through posts again to see. Absolutely correct. Old school low performance heads have a pushrod "slot" that guides the pushrod. Hi performance heads have a larger round "hole" that requires guideplates or self aligning rockers.
 
#13 ·
Thanks so much for all of the help! So I guess I can use the self-aligning rockers that I bought (just without guide plates - which I don't have anyway).
About the cam, the short answer is that I don't know. I brought an old 350 to a machine shop that came highly recommended in the area. And magically, a rebuilt engine was dropped off a couple of weeks later. I made several calls to inquire about specifics, one of which was the cam. I never got a definitive answer.
Mike
 
#14 ·
Based on all of the excellent feedback I got, I chose to replace all of the arms and pushrods. I went carefully one by one, and am ready to do a break in. I started it briefly, and noticed a very slight clicking. Can I run the full break in and then adjust, or should I go perhaps a 1/4 turn tighter? To ball park it I went 0 lash + 1/2 turn. This is with hydraulic lifters.
Thanks again for all of the help!
Mike
 
#17 ·
I spent some more time carefully adjusting the arms, and everything sounds good, engine runs great.
Although, I have been out for a few runs and just noticed steam from the radiator overflow hose when I got home - which is something I don't think has happened before. Coolant might be boiling? I always keep an eye on the temp gauge and it looks right on target. I will check the rad cap, and thermostat, hoses, etc. But I am just wondering if this could have anything to do with my rocker arm adjustments, or might this just be a coincidental problem?
Mike
 
#18 · (Edited)
I would replace the broken one. Might have just been a manufacturing defect. If another breaks i would investigate cause.

Now since you are noticing a defect in another, I would investigate. Maybe verify pushrod length. From experience, I discovered the hard way that incorrect valve train geometry will damage rocker arms and pushrods. My guess is that the pushrods are not the correct length. Don't follow the summit racing video on pushrod length, the wear mark method is not the best way in my opinion. Use the mid lift method. Using that method I have had no problems since.

I would think coolant going out the overflow is normal, removing excess coolant, so long as the thermostat or rad cap is working properly. It's totally normal for some coolant to be in vapour form. If your engine goes way above halfway on temperature gauge that may be a sign your thermostat failed. Otherwise it's something else.
 
#20 ·
Running too lean will make it hotter. Also too far advanced timing will increase temperature too which also depends on your compression ratio, but you will lose power if your timing is too retarded. Rocker arms I don't think have too much effect on the engine temperature.

I would check air/fuel mixture first. Then timing.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top