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My son and I are tearing into a 1955 M38A1. We have come a long way form when we towed this thing home! It ran well and did not smoke. The engine has a rebuild tag from the early 60's. We removed the tub and doing a frame up restore. IN part of the refresh we decided to at least go in and replace the front and rear oil seals as well as new gaskets and inspect all the internals while we were in there.

Removing one of the head bolts it became obvious that someone used an odd bolt in the front left location. WE had to wedge under the bolt head to make it back out of the hole. Once we had the head off it was visually apparent that the threads are nearly gone. The bolt they did try was longer than the stock length and think it bottomed out against the exhaust manifold stud that is just below this bolt. The ape behind the wrench kept turning and I'm left with the results. Good news is that the head gasket did not seem to be damaged nor leaking in that location. The bolt was rusted badly and I suspect it's only a matter of time and it would have been leaking coolant.

So now I need advice on how to repair. I am leaning toward a Helicoil kit with the longer 0.875" threaded insert vs the standard .656" depth. I've also read some good and bad reviews of other insert types (Time-Sert and others). I've used Helicoils in aluminum in the past with great success so I was leaning that direction. Any advice pro or con I'm all ears (and eyes).

BTW - I could go with studs if I have to but would like to avoid it if I can. Out of originality if I stick with bolts what bolt sealer do you recommend to keep coolant from seeping up through the threads?

http://www.repairengineering.com/e-z-lok.html
This is the style insert I like the best if you have enough room to drill the hole out and tap it for the insert.

I would use a Helicoil if this were mine, and permatex ultrablack rtv to seal the threads.

My vote is also Helicoil and the old standard Permatex Aviation Sealant #1. I prefer to drill and helicoil only as the last result. When I do use a helicoil I try to make the installation a stud instead a bolt. Helps keep the now slightly weaker helicoil from deteriorating faster with repeated use.

I have used both heli-coils and the E-Z-LOC system with success.

In cast iron I prefer the E-Z-Loc, especially where it goes into a water passage. The E-Z loc has less pathways for water to travel. They are inexpensive and easy to install with common tools. Like heli-coils, you will need to buy the appropriate drill and bottoming tap. E-z LOCs are all based on standard thread sizes, so you may be able to borrow a tap and drill if you don't have the larger sizes. For example, a 7/16-14 E-Z insert you will need a 17/32" drill and a 5/8-11 bottoming tap.
They are readily available on Amazon, thru Flea Bay vendors, and industrial suppliers like ZORO Tools. Pack of 5 on Zoro is less than $14.

Another thought, regarding your manifold studs. Remember that the stud that got plowed into by the head bolt will be particularly difficult to remove should it break in the future - the threads will be peened over. Might be a good time to replace all your manifold studs with quality replacements. My experience is they snap at the least convenient moments. The rear most stud is a real task to replace with the engine in situ.

Dittos on the Permatex #1 - on all the head studs and bolts.
Jeff

PS:

BTW, being a bit slow, I had to read WESK's comment twice on the Stud vs Bolt when there has been a thread repair.
Great suggestion Wes!
Jeff

Yes, as stated, go with Heli coil and a stud and Permanex it as usual. Do not run head bolts into Heli Coils.