Aluminum rocker arm failure - replace one or all?

I experienced a failure on one aluminum rocker arm on Monday. See attached picture. The rocker arm split in half right where the adjusting screw is. The engine is a 383 big block, with a .550 lift mechanical roller cam and matching double springs on ported cast iron heads. My set of roller rockers is from Hughes Engines, but this post is not meant to knock them. It is merely to get some feedback on what I should do. The failure occurred right off of idle, as I was SLOWLY accelerating from a stop sign. Out of nowhere a loud ticking noise developed, and I knew it was wrench time.

So if one rocker arm failed, should I be concerned that the others might fail? The engine has about 5,000 miles on it. All of the other rockers look OK (no signs of stress cracking or fatigue). Should a person not run aluminum rocker arms with a roller cam? Or is this an isolated incident? Should I check the head for something weird (stuck valve or something?). In an ideal world I would replace the one rocker and get back on the road, but more importantly, I want to do what it takes to not have future failures.

5000 miles isn't enough for a fatigue issue to occur.

I'm thinking the rocker was running up against a hard stop at some point.

It could be just that cylinder or valve, it could be all of them.

I'd suggest a dye penetrant test on all the rockers. Cracks start from the outside in, so PT will tell you if there are other failures about to happen.

But more than that, you need to find the root cause of the failure.

R.

I broke a Mopar alum roller rocker (same as a Crane gold). Took a while to understand why, but it turned out that the ground electrode came off of the spark plug and momentarily created a solid "hit" on that valve rocker. Replaced that one rocker and still run them now, 2 years later with no problems.
In your case though, seeing where its damaged, I'm wondering if its possible that the jamb nut was over tightened, causing the inital weakening. Just an idea, but I do agree, you gotta find the root cause of the failure.

Brian

I'd check clearence at the retainer, over tightening the lock nut could cause that.

Check your P to V clearance... but if thats plenty then
I would pull the spring and see if the valve is bent
or the spring ins broke... if thats fine then I would
see what the rockers can take for max open pressure..
if it is all fine then I would just replace the
rocker and move on.... I've only seen a break of
that nature when something bottomed out... even a
over tightened lock nut shouldnt do that... that
would tend to rip the threads out... JMO

I checked the PV clearance when the engine was being assembled, I do not have the spec handy but remember it being adequate. However I will check for a bent valve and broken spring. As a side note, the engine had just come up to full operating temp of 180° whe the rocker arm broke.

How much adjuster thread was exposed?

If you find no interference and you didnt over-torque by a bunch. Check to make sure you have high enough spring seat and open pressures.

Yes, HIGH enough. (some margin is also a good idea)

Just to let you know I have been these Hughes rockers since 2011 with no problems. How long have you been using them rockers ? Ron

I first built the engine in 2004 with the Hughes rockers. As stated earlier, only driven about 5k miles since.

If it has been driven 5k miles I doubt it was a probelm related to PTV clearance, it would have happened right away. Still check for a bent valve just to be sure....

Overtightened nut sounds probable....

maybe your spring pressures are too stiff for those rockers to handle, check that and call Hughes and see if they are within spec.

Check everything closely.....if all looks good, I guess Id just replace that single rocker.

Im no expert...Im usually just asking questions and learning as I go.... most people on this forum may be more knowledgeable, but if it was my engine I guess that would be my game plan.

I have a very similar combo 383, .600 roller cam and Mopar (Crane) 1.6 rockers and I split one in half right off the shaft a few weeks ago. I had changed my burnout style and was letting the 3 step limit the RPM's at 5200 and about 5 runs doing that one broke. So apparently getting into the 3 step during the burnout is a little rough on the valve train. I've since upped the burnout chip to 5800 so it barely if at all hits the limiter. It happened at the track on the 1st time run and I swapped the broken rocker for a spare, replaced the bent pushrod and have probably made 50 passes since (blessed with 2 runner-ups & 1 win). So I think swapping the rocker will be just fine. I checked valve lash again last weekend and it was spot on.