Head Stud pulled out
 

While torquing the head studs in a cast block the threads pulled out in one hole. If I put in a heli-coil will it hold the torque?

Yes

Absolutely agree. Many years ago we had a student run a 7/16-20 tap through all 17 head bolt holes in one side of a 350 Chevy. He thought he was "cleaning up the threads!". Of course we questioned him about the huge amount of iron chips this "cleaning" had produced. We ended up putting 17 heli-coils in that side of the block and it worked out just fine. He will never make that mistake again.

The Heli-Coil--properly installed--will absolutely hold the torque. Stronger than the cast-iron threads ever were.

But Pontiac blocks are bad about bore distortion from head-bolt torque to begin with, (even though folks think they shouldn't be, considering that the head-bolts go into holes anchored away from the cylinder bores) and a Heli-Coil may change the amount of thread engagement in the block, and the way the block is stressed by that torque.

Quick 'n' dirty thread repair? Sure.

In a perfect world, you'd fix any other marginal threads in the deck surface, 'cause all those holes have had the same stress as the failed one, and then have the block torque-plate honed so that the cylinders come out round AFTER the heads are torqued in place. But this gets expensive, quickly.

Remove all doubt and use 2 helicoils (i might have trimmed 1, forget.)

I've used heli-coils in the past with good success but never in a hole that was torqued to 95 ft. lbs. I just wanted to know if they were strong enough to hold that much torque. Thanks for the replies.

Yes .. I have not done to many Helicoils in the past but a few with no problems.. https://www.mcmaster.com/products/he...d-size~1-2-13/

I would pay attention to depth / length of coil to get as much thread engagement as you can for obvious reasons. I would want more than minimal 1/2 depth

Only caveat would be if the metallurgy in surrounding area is sub par .. But Helicoil will be better than original even in that case

Heli-coil brand says you can stack them, but I have never been thrilled with doing that. I always seem to have a snag as one coil ends and the next one begins. McMaster Carr offers the coils in various lengths for your purpose. You can probably find a coil close to the ideal length. Also, make sure the coil enters a chamfered hole and rests a full thread below the surface so there is no chance it pulls out the top and rests in the gasket.

GM recommended a product called a Time Sert for the head studs on Corvairs. They are notorious for the long studs pulling out. The benefit is that they are available in different lengths to fully repair the threads without stacking inserts.

Is a 3/4 length helicoil adequate of should I go to a 1" length. The 3/4 is 1.5D and the 1" is 2D. The 2D is harder to find especially in a kit. I don't want to stack two helicoils and risk they won't line up so the the lower one will engage the threads.

Is it still a blind hole? that effects length of what you can put in it, Taking in account a heli'tap isn't going to fully reach the bottom to form threads for the helicoil

I had one Pontiac block where i was cleaning out the head bolt hole/threads and the bottom fell out from a incomplete pour

If i needed more thread in a blind hole i have removed a portion of the taps lead in to get it, .... even on a bottoming tap just that there is less that can be removed and have the tap still cut

What was the original thread engagement of the bolt in the block?

Schurkey

Not bolts but studs. I couldn't tell you the exact amount of engagement but for sure it wasn't enough.

OK.

Should be easy to determine. How far down in the block are the threads damaged?

Doesn't matter I am using 1" long helicoils

Time Sert. - works good, lasts, used em😀

Time Certs are really nice and essentially a thread repair solid bushing. The kits are much more expensive, about 3-5 times the cost of a coil style repair kit. It's a good option if cost is not a factor. Not quite as forgiving as a coil type repair. Work should be done in a mill or at the very least, you need a drill bushing to make sure the hole is perfectly straight. Time Cert kit on Amazon $149.00 Heli-coil kit $26.99.

I installed a helicoil. the hole isn't quite deep enough for a 1" so I installed a 3/4". I'll be holding my breath with I torque the heads.

The thread engagement with stock bolts is right at 3/4.. I didn't think the hole and or ability to thread it for helicoil was deep enough for 1"

Be brave, TQ to 95, and be happy.


Re-TQ all after some miles.