Roller Rockers in Stock

[Jeff Lee]

Todd,
One thing I never mentioned. My Stocker AMX was shifted at only 6500 RP, launch @ 5800 RPM. I wouldn't conider that excessively high for a 4-speed Stocker. Though maybe that's high for a Pontiac...

Regarding breakage, I not only experienced the pushrod through the rocker cup, I also experienced the rocker arm lifting at the folcrum numerous times. How could that occur? Just as SSDiv6 has stated, it's from inferior production techniques. Simply stamping out a rocker arm on a cold plate of steel stretches the metal, especially in the area where the rocker ball situates. Since this area is the receipient of the most stretching, this is the weak area. I'm not an engineer but I would suspect any area stretched into a ball or semi-ball shape would be weak. Thus the breakage at the (1/2 round) push rod cup and the rocker ball folcrum area. What I witnesed each time the folcrum area failed was (typically) four stress cracks that originated from the very bottom which traversed vertically. In essence, the rocker arm was attempting to pull itself away from the rocker ball. The rocker arm would mushroom out in this area never leaving parts behind, they would just flare outwards. I always considered myself very lucky that a broken rocker never caused other engine damage. Broken lifters (Schubecks) are another story.

A local friend of mine by the name of Ron Smith still owns the '72 Duster 340 he bought brand new with the specific purpose of racing in Stock (H/S). That's a hydraulic cam, low-compression 340 T-Quad engine. Back in 1972 he was breaking factory rockers. Only now will he addmitt to "cheating" by running the HD Direct-Connection stamped steel rockers (which I believe were the receipient of a heat treat process or maybe just the A+ parts off the assembly line; before the allowance of Isky ductile-iron adjustable rockers in Stock to non-OEM equipped MOPAR small blocks). Only then did the breakage trickle down. So that's at least one racer I can name who can valididate problems with a shaft-mounted system before the advent of really radical spring pressures and cam lobes. I have spoken to others but I can't remember enough of the specifics to bother with mentioning them as sources. So again, this is not a new phenomenom (sp?).
As SSDiv6 keeps trying to drive home. this is primarily a problem with inferior parts.
Thanks,
Jeff Lee