It would be interesting to see the two broken off pieces with adjusters as you found them just for comparison purposes. I wish you the best, like, hope nothing else is bent.


64F100 57FAIRLANE500

The rocker arms are reasonably robust so they don’t break without a reason.  Can you identify exactly which rockers and pushrods (intake/exhaust) had the problems?  What kind of valve lift numbers are you running?  Assuming you have ruled out old or sour gasoline, a couple of things to look at would be valve spring coil bind or retainer to guide interference.

Lorena, Texas (South of Waco)

Isky 301333 cam. .448 lift. They both appear to be exhaust valves. It's the 5th rocker from the rear on the passenger side and the 4th rocker from the rear on the driver side. The sour gas is certainly a possibility. The fuel in the tank is approximately 6 months old now, maybe a little bit older than that. 

a friends 56 sat for the winter and done the same thing.broke a rocker.no other damage and it didnt do it again.i didnt think they would break that easy.

I am running the same cam in my 292 with flat top pistons.  I have stock 1957 "G" heads and rockers with stock valve springs and tubular push rods.  I set my valves at .018" hot and never had a problem.  It would take a lot of force to break those rockers.

Are those FoMoCo rockers?

Yes, they are FoMoCo rockers. Isky #6005 springs, which are 135lbs at 1.750" seat pressure and 285lb open pressure. 

So I had planned to remove all my rocker arms that were on this engine and replace them with the rocker arms off of my old engine. Upon further inspection, the rocker arms that were broken are the ECG, higher lift (1.54) rockers and the ones on my core engine are the lower (1.43) ratio. The specs on the camshaft are all based on a 1.5 ratio rocker arm. Would I see a big difference between the two? I'd planned to swap the rockers and reinstall everything once my new pushrods came in and then rotate the engine by hand while checking for coil bind. I wonder if that slight difference in lift would keep the coils from binding, if that was ever my issue in the first place. Just trying to avoid having to take these assemblies apart over and over again, but I may have no choice. 

So I set one head with the 1.43s and one with the 1.54s. Both are causing coil bind on the inside valvespring. I've emailed Isky to see if they have any suggestions. The heads have been milled previously and the block was decked a minimal amount when I rebuilt it, but I have no idea how much has actually been removed over the years.

135# on the seat sure sounds like typical Isky. For a street engine 135 is a lot to me. Our 7000 rpm flat tappet cam dirt track engine will run close to that but my 6000 rpm 6’s stay closer to 110 or under. May not have anything to do with the breakage but over time will cause some fatigue from my experience. Good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.