Ever hear of this??!!

earthquake68 · #1 07-20-2013, 10:31 AM

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.

Ms Grumpy · #2 07-20-2013, 08:35 PM

Alan that engine has is out for you.

carpoor · #3 07-21-2013, 09:03 AM

How is the swipe on the valve stems?

earthquake68 · #4 07-21-2013, 09:27 AM

They're almost perfectly centered. I checked. This thing is haunted.

BillsCamino · #5 07-21-2013, 10:43 AM

ARP bolts and studs have rolled threads.
I wonder if this batch just happened to be slightly undersize in diameter and were overlooked by Quality Control...
I'd mic the stud diameter (and pitch diameter if possible) and compare those measurements to a known good one.

earthquake68 · #6 07-21-2013, 06:51 PM

Bill. That's the only thing I could think of that could be wrong. Under load, the nut would pop up a thread or two and get loose from there. I guess I'll figure it out when I tear it down and mic everything.

carpoor · #7 07-22-2013, 02:29 PM

Quote:

Originally Posted by earthquake68

They're almost perfectly centered. I checked. This thing is haunted.

I kinda figured you checked it. I am leaning towards what Bill said.

earthquake68 · #8 07-23-2013, 05:47 PM

Well, I FINALLY figured out what was wrong with the GTO. After I took it apart, I saw my side of the engine held together. Nothing loosened up at all. ......and that was the problem. Whatever jack hole came up with this combination should have his finger nails removed with rusty pliers and forbidden to touch another tool as long as he lives.

The problem was the combination. He had oversized, triple valve springs on a relatively stock, flat tappet cam. ...That's over SIX HUNDRED psi open! These are the springs you need to run a full roller cam with gross lift in excess of .600". The adjustable stock Chevy nuts couldn't hold that kinda' force and slipped up the studs. The only reason the studs didn't fly out of the engine was because they were ARP studs. Since I got the valves to hold adjustment, all that force was displaced to the next thing in line. .....the cam. It snapped the cam off clean in between two bearings.

The engine is getting pulled tomorrow and sent to the machine shop. The combination didn't work at all anyway. A stock engine would've outrun this turd.

Bigger is not always better, and more expensive doesn't mean faster. Do your research and come up with a combination of parts that works well together. Or you could just throw money into a burn barrel. It'll have the same effect in the long run.