A '67 GTO came in the shop. It had a bent valve and broken push rods. Just so you know the whole story, it has a 389 4 barrel in it. Someone, at some point, converted the Pontiac valve train over to big block Chevy. That is actually pretty common. Pontiac uses 3/8" rocker studs that tighten down to zero. (that is, there's no adjustment. They tighten as far as they can go and that's it) Big Chevy uses 7/16" screw in studs with lock nuts to adjust the valves.
Now for the aggravating part. We replaced the broken pieces and sent the head out to be repaired. We put it all back together. The head has ARP studs, brand new lock nuts and comp cams roller tip rockers. As I adjust the valves, I notice there's not much tension on the nuts. By the time I adjust the last cylinder on that head, (the engine was running) the first cylinder had loosened up. WTF??!!
Ok, cheap aftermarket lock nuts. I put the O.E. stuff back on and it seems to hold the adjustment. Five minutes later the owner comes back with it bucking and coughing. The valves lost adjustment again. W.T.F.??!!
Ok, I'll fix you! I take everything back apart. Clean all the studs and blue loctite all the studs. Then, after I get the valves adjusted, I take a punch and hammer and pien the nuts into the studs. There, that oughta' do it.
I take it for a test drive. ONE MILE LATER, ...the friggin' valve are clattering. YOU GOTTA BE KIDDIN' ME??!!
Ok, sucker, I got your number. The studs are long enough to jam nut them. I put jam nuts on all the studs. I crank them down tight. I take it for a spin. It seems to be fine. The owner jumps in and takes off. The engine flies to pieces less than a mile away!
There are no words to describe how mad I am about this. The studs ARE NOT pulling out of the heads. The lifters ARE NOT collapsed. The cam IS NOT wearing lobes off. When I pull the rocker cover, you can physically SEE the nuts backed off the studs. Short of welding the nuts to the studs, I have NO . FREAKIN'. CLUE. why this is happening. In 30 years of building engines, I have NEVER had an engine that straight out REFUSED to keep a valve adjustment.