Anyone ever break/bust/crack/fracture the factory 273 adjustable rocker arms?

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dibbons

dibbons

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I just had two sets of 273 rockers/shafts reconditioned at Rockers Unlimited. Used to run these back in the day on my 273 bracket car. The current ones will be used on a 340 and 305 (de-stroked 340) I am building.

Just wondering what kind of failures (if any) others may have experienced. Fotos would be interesting, as well. Thank you.
 
Ran a set on my roller cam 408 4 speed for a few years. I regularly spun it to 6k. Never once did I have an issue with the old ductile iron rockers. They are tough.
 
Actually I believe the 273 rockers are forged, not cast, and they're pretty damn tough.
 
dibbons said:
I just had two sets of 273 rockers/shafts reconditioned at Rockers Unlimited. Used to run these back in the day on my 273 bracket car. The current ones will be used on a 340 and 305 (de-stroked 340) I am building.

Just wondering what kind of failures (if any) others may have experienced. Fotos would be interesting, as well. Thank you.
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Read the thread on the broken PRW rockers. If you are running anything other than stock, even with 273 rockers you need to correct geometry.
 
ran the 273 rockers on stocker 273 years ago, spun to 7500 . never broke one. now use them in 340 stocker and spin them 7400 rpm . with a lot more aggressive cam profile. never broke any!! yes they are forged.
 
can you say bulletproof? Ductile iron is cast, not forged but is hardened by a process to make it more impact and fatigue resistant than pig iron. Its very difficult to forge iron.
 
I feel sure somebody has broken some, but I haven't seen one.
 
All of the ones I've seen broken, including my own, have been ones that were relieved for spring/retainer clearance. Naturally, the amount of "relief", spring pressures, lobe profiles, if one is getting into valve float and time, have an influence on their life expectancy. Same with aluminum roller rockers.
 
I ran Isky double valve springs with dampers and aluminum retainers with a .580 lift Isky cam for years and never even thought to check for spring/retainer clearance. (I know I machined the guides for teflon seals and the valve seats to accommodate the springs, but never touched the rockers)
Makes me wonder under what conditions there would be interference.
 
dibbons said:
I ran Isky double valve springs with dampers and aluminum retainers with a .580 lift Isky cam for years and never even thought to check for spring/retainer clearance. (I know I machined the guides for teflon seals and the valve seats to accommodate the springs, but never touched the rockers)
Makes me wonder under what conditions there would be interference.
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I have a 360 in the shop I built for a customer. We went with the Comp 901 spring and I had to clearance the rockers.
 
Thanks, RRR. That's funny, my machine shop just installed 901 springs on one set of my cylinder heads. I have Mopar 340 performance springs P4120249 (factory 340 style) for a second set of cylinder heads. Should be interesting to find if I need to clearance either setup (I hope not, don't want to weaken anything). I wonder if the clearance problem is the fault of the retainer (and not the spring diameter).
 
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I wonder if RRR can tell me if the 901 springs he installed on the 360 (assuming the 360 has the 273 rocker arms) have a yellow identifier stripe. My machine shop, at first, could not remember what springs were used and I would love to double check:

DSC01173.JPG


DSC01177.JPG
 
pishta said:
can you say bulletproof? Ductile iron is cast, not forged but is hardened by a process to make it more impact and fatigue resistant than pig iron. Its very difficult to forge iron.
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Right, that's 'cause they're forged steel, Crane offered ductile iron rockers tho'. I read a
bunch about the modified nodular iron used in the new drop spindles out there.............
 
901s all have that yellow stripe. Least all the ones I've used over years have.
 
dibbons said:
Thanks, RRR. That's funny, my machine shop just installed 901 springs on one set of my cylinder heads. I have Mopar 340 performance springs P4120249 (factory 340 style) for a second set of cylinder heads. Should be interesting to find if I need to clearance either setup (I hope not, don't want to weaken anything). I wonder if the clearance problem is the fault of the retainer (and not the spring diameter).
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These were hitting the spring itself.

And yes, these have yeller stripes too.
 
Killer6 said:
Right, that's 'cause they're forged steel, Crane offered ductile iron rockers tho'. I read a
bunch about the modified nodular iron used in the new drop spindles out there.............
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Im no metallurgist, just what I read from books. "...The valvetrain consisted of a cast nodular iron camshaft, solid or hydraulic lifters, solid pushrods and shaft-mounted, malleable iron rocker arms..." (Allpar.com) Malleable, nodular, ductile, pearlitic all seem to be somewhat interwoven in their definitions.
 
Ran 273 rockers in a 13:1 340 with Crane triple valve springs spinning to 7800 RPM back in the eighties. Never broke a rocker, bent a lot of pushrods, but never broke a rocker.
 
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