I just discovered a rocker arm on my small block that loosened up and popped off the stud. It kinda mangled the threads on the stud, so I’m going to replace the stud, poly lock and the rocker just to be safe. I think I may not be applying enough torque on that Allen lock nut, but I’m afraid it will just strip the inside of the Allen lock nut if I lean on it. Is there a trick to getting this tight enough?S.B.
Yes. The poly lock nut for roller rocker arms is a great little invention. I learned the little secret to locking these nuts tightly from an engine builder probably 40-odd years ago and the technique is simple and works extremely well.
The poly lock nut is merely a threaded nut with a small Allen screw placed inside the female threads. With the large adjuster positioned to set the lash or lifter preload, then the Allen nut can be tightened. But sometimes the Allen won’t tighten against the top of the stud tight enough and the large adjuster can then work its way loose—as you’ve discovered.
The technique is to set the large adjuster nut to just shy of the final position of the poly lock. With the large nut in this position, tighten the Allen wrench to contact the end of the stud. Then tighten the large poly lock nut the last 1/16th of a turn or so. This places more load on the locking Allen plug than can be accomplished with the Allen wrench alone.
This does require some practice to get the setting correct, especially when setting lash on a mechanical lifter engine since you’re working to within 0.001-inch. This requires a technique where you can estimate the amount of change that last 1/16-turn will affect the actual lash. It can be frustrating but with some experimentation, you can come up with a technique that will produce the desired lash.
One other little tip we’ve learned is that ARP makes a great adjust nut called a Perma-Loc with a simple yet very helpful addition. All other poly locks use a six-point hex that allows a box end wrench to fall past the hex, requiring you to hold the wrench in position on the hex. The ARP Perma-Lock uses a 12-point nut with a shouldered ledge on the bottom of the points that prevents the box end wrench from falling past the hex. Plus, the Allen set screw is machined flush on the bottom so it offers full optimal contact—as opposed to other adjusters that use a tapered face. This might seem like a small thing, but once you’ve used the ARP Perma-Locs you will more fully appreciate these features.
Another thing to consider is whether you are using factory rocker studs or not. Factory rocker studs were not designed for a set screw to contact them and don’t have a flat top surface, so the Allen may not be getting full contact either. ARP makes studs with a flat surface.
How about correctly identifying the engine in the photo, It’s obviously not a SB Chevy. It’s a BB.
Hey, thanks for the heads up–we’ve made the adjustment.