Broken rocker arms two weekends in a row

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Les Gibson

Les Gibson

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Asking if anyone might have any thoughts on what might be causing this.
For consecutive weeks I've broken an exhaust rocker arm. Last week #4 exhaust rocker broke. This past Friday night #5 exhaust rocker broke. These are Harland Sharp rockers installed on Mopar Performance aluminum W5 heads. There's no oiling issue or clearance issues. I am told by the previous owner of my Arrow that these rockers are about 6 years old. Is this a case that they're just wore out and I need a new set or is there another reason. Appreciate any constructive thoughts.

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Is it possible you're spanking a valve, I used to poke a pushrod thru when I missed a shift and spanked a valve.
If you got a bore scope, see if you can see a witness mark on the piston.
Maybe interference with the retainer and top of the valve guide.
Weak valve spring ?
Same cyl ?
 
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How about a close up pic of the break.

My recollection is the SB rockers are quite thin adjacent to where the bodies are counterbored for the bearings.

My thoughts are, either the rockers are reaching the end of their fatigue life……..or the springs are going away and as a result, the Valvetrain isn’t as happy as it could be/once was.
If the springs are total “overkill”, then the service life of the rockers will be shorter.
 
Actually, you can see it here……. Not much material there at all.
The wider body of the intake rocker would have the load spread out over more material.

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inertia said:
Is it possible you're spanking a valve, I used to poke a pushrod thru when I missed a shift and spanked a valve.
If you got a bore scope, see if you can see a witness mark on the piston.
Maybe interference with the retainer and top of the valve guide.
Weak valve spring ?
Same cyl ?
Click to expand...
Did that, no evidence of any witness marks on the pistons. These valve springs have around 120 mostly 1/8th mile runs on them since installed new. Can't see any sign of retainer to guide interference. First rocker that broke was #4 exhaust, second broken one was #5 exhaust.
 
Any indication the retainer is sawing/marring the rocker at the break.
2 Diff banks, gotta think interference, timing chain ?
Fatigue, sure, agree. But what are odds of 2 conservative wknds.
More likely something changed.
jmo
 
I had the same problem with Indy rockers with 600# pressure over the nose springs, lasted about 2 years before they fatigued to the point of snapping in the same area as yours one right after another. Have two friends with big block Chryslers with Harland sharp rockers, back in the 90's with high rate springs do the same thing. They switched to solid body rockers(non roller bearing) One went to Mopar Perf. and the other went to Cranes. Like PRH said they were just to thin with the bearings in them.
Back then I ran W2's with 1.6 Mopar Perf. rockers, .630 lift and 420# over the nose for around 10 years with no failures. Sold the whole W2 setup and bought the Indy Brock heads and rockers. I've been running Hughes rockers since 2010 and on my 3rd set of 600# springs with no signs of the rockers stretching or ovaling around the shafts yet.
 
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Aluminum rocker arms, they snap occasionally. I’d call Harlan sharp and ask them the service life of the rocker arms for your combination. But before you do, check your springs,pushrods and valves. I’d pull a head and thoughly check everything.
 
That looks like fatigue life failure, or way too stiff a spring failure to me. Since it's been running for so long on those springs..... I'd guess fatigue life. The more spring, the sooner the rockers will fatigue.
It looks like a serious offset to the intakes. I would see if i could get eight of the non-roller bearing HS version that Mancini sells, and keep the high dollar offset intakes.
 
Aluminum has no fatigue strength. It continues to weaken till it breaks. Steel and titanium have a point where it stops weakening.
 
If you replace the rockers with stronger, problem won't take long to find, if it's something else.
Once is an anomaly, twice has a cause, in my experience .
 
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Maybe try to find some KYMDYE (sp) and check the remaining rockers for minute cracks.
 
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I can’t tell you how old some of my rockers are. I’ve never broke a Harlan Sharp, T&D, Indy, Crane, or Mopar Performance rocker. But when I’m building an engine I sometimes spend several days on Geometry. Zero broken rockers in 47 years.
 
When did the rocker break. After a run? Shortly after start up? Had the engine been run that day?
 
I go along with the "somethin's hittin somethin" crowd. That seems likely.
 
Only race every 3rd weekend. Just kidding......

Well that is what alum rockers do...There is no way of testing the ultimate fail strength of alum. You have to wait for the 'bang'...Steel does have a fatigue limit that can be tested for. Just beats me why people risk using alum rockers when there are so many stronger steel & S/s rockers available.

I see a number of reasons for these rockers failing, reasons either singly or collectively:
- valve springs too strong
- valve train going solid
- rockers weakened by fitting roller brgs
- less surface area on the exh rockers to carry the load.
- exh valves opens against combustion pressure, so more load on exh rockers, all else bing equal
 
I've heard that ignition cut two-steps can possibly ignite fuel in the exhaust that can unseat the valve. You can hammer a valvetrain to death if you unseat a valve on the base circle.
 
Geometry? Make sure the roller is in the center of valve at all times. Depending on the lift there are times we need to install longer valves and raise the rocker to bring the valve closer to the rocker shaft. When the valve gets longer and the rocker shaft is raised the spread gets closer due to the angle's coming together. Just ran into this on B1's with 863 lift.
 
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