Over the holiday weekend a friends boat started acting up like it had dropped a cylinder. Last night we found that a poly lock had failed allowing the rocker to come off. Basically the barrel part of the lock with the threads inside split into 3 pieces.

454 with a .600ish lift 230/236 duration at .050 lift roller cam. Engine made 496 horse on the dyno at 5200 rpm. Valve train geometry looked good when engine was setup.

Question, are these locks known to fail? The rocker itself was fine

I had one fail on a motor once. Possibly over tightened on jamb nut.

Check and make sure the lock is a .600 diameter and not a .550 diameter. They normally will crack if over tightened

Ok, I'll check that. Did the .600 replace the .550 or something? I had them pretty tight as I didn't want them to loosen up.

The crane gold is machined for a .600 nut. Which is beefier than the .550 nut. I normally set the lash, tighten set screw , and give them both a gentle "squeek" to snug them down. No need to go crazy tight on them .

Also, its good to make sure the tops of the studs are nice and flat, so the set screw gets a good contact area on the stud.

Had 20 of them crack on 2 575's because some hammer head snugged the set screw and then gave the nut some more.

Ok, thanks for the info.

Yeah, definitely didn't do that, just snugged the lock good with an allen wrench. This was run all last summer and this summer.