Knocked out a rocker stud after rebuild

[bowserb61]

I just put my 1959 beetle back on the road after a rebuild of the original 36hp engine. All stock spec, and NOS when available. However, I had a major failure about 1/4 mile into the first drive.

The engine started running rough and then not at all so I pulled over and looked it over to find that one of the rocker studs on the 1-2 side of the engine had been hammered clean out of the head.

As you can see, it took the aluminum with it and cut straight out. So here's the back story:

I first cracked into this thing because of a broken lifter guide and then started down the path of "well, while I'm in here..." The first rebuild consisted of a NOS camshaft, rebalanced rotary assembly, new rings/ honed cylinders and a valve job that retained the original valves.

Everything else was left alone, and it was driven like that for about 600 miles. As it turned out, the valve job wasn't done correctly and the guides worked their way down and shattered into the 3-4 cylinders, meaning I had another tear down to do.

The old pistons/cylinders were good enough to use, but not good enough to repair, so I replaced them with a stock Kolbenshmidt set, and sent the heads to Rimco to have the debris damage repaired and have new, shouldered valve guides installed. Without asking me, Rimco replaced my original intake valves with Wolfsburg West parts "just to save time by not cleaning the old ones." Since I have never been more than unimpressed with WW parts, I got a whole set of NOS ATE intake/exhaust valves and swapped them out. The exhausts fit fine since the guides were ground to my original ATE valves, but the WW valves had smaller stems than the ATEs so the ATEs didn't fit and I settled for the WWs, not wanting to pay for a third valve job just to have it done right.

This is how it was set up when I started it a few weeks ago. I ran it in for 20 minutes at 2000rpm with no noticeable issues and then turned it off and let it sit for a little while. Before driving it, I opened the valve covers and checked all the rockers by hand to make sure nothing was too tight or too loose. All the valves had been adjusted to 0.006" when cold. I then did some first gear/ reverse gear driving in my driveway before taking it on the road where it did the damage in the pictures in a quarter mile or less.

After I found the problem I immediately checked that none of the valves on that side were stuck, and they all moved freely when pressed with a screwdriver heel.

Repair isn't a big deal, I'll just use a helicoil and put a new stud in (unless there's some special reason not to use a helicoil on the head). What I'm concerned about is WHY did it do that? Did I shoot myself in the foot by swapping the old ATE exhaust valves for the NOS ones? Was it just a weak spot that failed under the new, higher compression of new valves, pistons and cylinders? Does this point to some fatal flaw in my build, and can I expect this to happen again if I just repair the stud and keep going?

Sorry for all the text and thank you for any useful input you may have.

[57BLITZ]

[Cusser]

[60ragtop]

x2 on the time sert and probably just old age made it pull. Has happened to me several times on my 36HP engines
_________________
Rick
Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

[Zwitterkafer]

I wouldn't use a helicoil there. IMO drill and/or tap oversize + step-stud would be the way to go. Was the rocker shaft tilted out of that one saddle? Maybe even better to replace both studs on that head. If it was coil-bind, I'm surprised that the first test running did not show a problem. A rebuilt engine should always be turned over slowly by hand to check for any unusual resistance or tightness.
Good luck, and may the heads always look that clean when you remove the valve covers!
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"Criticism comes easier than Craftsmanship"
- Zeuxius, 400 BC

[richardc]

Helicoil will work fine.
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1970 Ghia vert

[bowserb61]

Thanks for the replies. I will definitely check that the seat shoulder isn't contacting the spring cap, but I know that they were fully seated when I installed the valves, so I would hope that's not the case.

Of course at the very least it was turned over several times when I timed it and set the vale gaps and nothing was seemed tight or unusual. Even when I checked right after the 20 minute run-in nothing seemed too tight or too loose and that's part of why it worries me. It seems that whatever happened only happened under the load of driving, and not just running at idle or holding 2000 rpm. I could be satisfied with the old age explanation, but I still wonder why now an not before, and why so suddenly after I started driving.

The only issue I see with a helicoil or time sert is the fact that the face of the hole is in that concave cylindrical seat. The time sert would have to be counter bored deep enough to fall below that profile. I think the best option would be if I could find a stud that was a step larger on one end and the original size on the other.

[60ragtop]

when I installed a timesert and couldn't sink it far enough, I just used a file to make it flush so the rocker would fit. Lasted 130 K +
_________________
Rick
Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

[eyetzr]

You should check the other side as well. Heli coil may work, step stud would be the direction I would go. Good luck
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I think he meant "rare", as in "not well-done"

[stanovich]

looks to me that the stud was too long and jacked itself out when it was torqued. heli coil should work .I would pull all and check depth of hole and stud length. time spent now=money saved later.

[bowserb61]

Just to button this one up, I ended up pulling the head and running a helicoil just far enough not to interfere with the seating surface. I've got about 200 miles on it now. I've been watching the valve adjustment pretty closely and there's no sign of anything coming back so I think it was a successful fix.

My best guess is that I just over torqued it during assembly and made the initial break and the engine did the rest. I'm always very nervous about threading anything into these aluminum/alloy heads for that very reason and I guess it finally got me.

[Bug-nut]

Glad to hear you got it all straightened out. I recently rebuilt my 36 hp '59 Beetle engine also and ended up using WW valves and guides - I hope they don't cause me any trouble...
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1959 Fjord Blue Volkswagen Beetle
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1962 Austin-Healey Sprite