Technical Broke another rocker arm

This is the second one on my daily driver 64 El Camino in 6 months. Junk metal? I had one in a customer's small block just last week break. Took another one out of my pile of parts slapped it in everything is fine. Weird stuff

 

How old are they, do you have coil bind or were you winding the hell out of it?

 

That is weird! Only other broken one I saw the push rod poked through the socket.

 

You didn’t really break another, one in your car and one in a customers if I read the post correctly?

Nevermind, I re-read the post correctly this time

 

I've never seen that happen before. All of the small block Chevys I've worked on have been stock or near stock.

 

Is it the same rocker arm position?
I'd be wondering if that pushrod is possibly a little bit longer than the others?
Don't know, just thinking out loud.

 

I had a 351c that would break a rocker arm fairly regularly. Always a different one. Sometimes intake and sometime exhaust. Broke one while it was idling.

 

Usually with coil bind the pressed in stud will work loose, but it screw in something has to give. Like asked is it the same one? Might be a lifter pumping up and getting stuck? Just thoughts.

 

There is a thing called metal fatigue, pulling parts from a stash that are fifty years old has it's draw backs.

 

Blowing up the pictures, it looks like it took a chunk out of the top of one of the keepers for the valve spring?

 

This one happened on the opposite side of the engine then the first one. I was cruising along about 1,900 RPM and then pop pop pop pop pop through the carb. The engine is a 383 that is very mild and who knows how old the Rockers were

 

Post a picture of the underside of the rocker arm.

My guess is it's hitting on the retainer.

That push rod is junk as well and from the pic looks like it might be rubbing where it comes through the head.

 

Supposed to rub, thats what guides the rocker.

 

Not to the point there are filings on the head. It can't bind in the hole.

Typically on OEM castings you'd enlarge the pass-through holes and run guideplates.

 

Looks like you were close to dropping a valve.
I think you had a good day.

 

Had a few in the 70's on my 396 and always pulled that head for a valve check/job just in case.....really got old....

 

Not just random failure; something's wrong. Look for evidence that the end of the rocker slot was contacting the stud. Too long a pushrod or too much lift can cause that. Coil bind or overly stiff springs are other possibilities. Millions of Chevys have done billions of miles with those rockers; "junk metal" is the least likely cause of your troubles.

 

Years ago in my Dad's dirt track modified we were breaking stock stamped steel rocker arms, i turned out the engine builder was angle milling the heads on the intake side for more compression and forgot to use shorter push rods.

 

I would look into this. From the pic it does look as if one or both keepers sustained some damage. The other thing I noticed is the oil passage in the push rod looks deformed or some shavings are sitting on the tip of the pushrod. The rocker isn't blue ing so heat wasn't a factor in its failure. Possible the geometry is way off.
Investigation time.

 

Looks like the top of the valve stem was ground down..
I would pull the engine and take it apart. I couldn't trust it. Something is dead wrong.. Can you get one of those cameras and send it into the spark plug hole and see if anything's hitting..

 

Or benefits, depending. I'll take a 50 year old OEM over a new Chinesium any day.

 

A few years back there was a bad batch of rocker arms.
I put a brand new “blue print” engine in and at about 50 miles the rocker broke. I called the manufacturer and they apologized profusely. They knew the supplier’s rockers were defective, thought they had recovered, changed all of them. They covered everything

 

That has to be caused by fatigue, not overstress. I build a SBC engine with my grandson years ago and we both thought the other had timed the cam. Neither had. We turned the motor over and bent a bunch of push rods and jacked several rocker mounting studs out if the head but rockers were fine.

I would be interested in seeing the base of the fracture and bottom of the ball socket. My guess there was a scratch or nick in the metal there. That would inevitably result in a fatigue crack being initiated. The fracture should have indications of a crack in that area that in time eventuated in the part breaking. That's why a lot of care is used to be sure parts that are cyclically loaded are smooth with no scratches or V-notches in their design. Fatigue failure happens at WAY less than nominal strength of a material. Realize we calculate stress at force over an area, or psi. when the area effectively is zero as in the root of a crack or scratch, or even the root of the stepped shaft with no radius, the stress becomes infinite - lbs/0.0.

A pretty nice fix would be just get one of these!!

 

Seen it happen many years ago. It was usually on high mileage 283's that spent most of their time being driven sedately...Then the driver goes on a long road trip breaking a few rockers. It was claimed that sludge limited rocker ball oil and they overheated and failed.
However, this failure is different

 

Not going to pull the motor.if I do it would be to replace it with 2 other sbcs I have.i put a rocker in yesterday and drove home 25 miles with no noise or problems.i will pull the vc and inspect the keeper for the valve today after work.

 

I wouldn't be so sure about that. It could be a random failure. Although, the age of the part increases the odds of failure a bit.

I've only had one Chevy stamped rocker really break like that, it was on a big block, and not very old.

It's a really good rocker arm design, but metal does fatigue after half a century, and millions of cycles of use.

 

From what I see in the photo... By the color and the grain size of the freshly viewed metal, that rocker arm started breaking a "long" time ago.

1. The dark color of the broken material says that, that metal has pulled apart down by the stud opening in very small amounts (micro inches) for a long time. Long enough ago to get oil into the crack. Plus the material is smoother, which indicates wear, or the material has been rubbing on itself for a long time. Again, in VERY small amounts.

2. Then in the photo, the rocker's upper right side, for some reason the grain structure is very course as compared to the rest of the broken material. This by itself is a weak point in the material.

I'd say, you've got a case of bad heat treating and MANY MANY, loading cycles (as in OLD and well used).

Just start with fresh, "known" lightly used or new rocker arms next time.

Mike

 

Here's some new pics. Degreased the rocker arm so I could get a good look at it and it looks kind of bad where the valve stem rides. Can't see any other cracks or anything else they may have caused it but we'll have to check out the top of that valve stem today.

 

To solve the problem....keep two spare rockers with you, along with the valve cover bolt wrench, and the rocker nut wrench.

The part broke after years of service, it happens. Don't overthink it.

 

As cheap as a set of good stamped SBC rockers are, I'd buy a set and replace all of them, just for peace of mind.