Exhaust Studs

[unplugged]

I am replacing my header. One of the studs stripped out the threads in the head. Upper R, facing exhaust ports.
The studs I used when I rebuilt the engine had only a 10mm section in the engine. That was many years ago and I don't recall why I chose them. I now know that was a bad idea but can't go back. There is a min. of 20m depth of thread in all of the mounting holes. I would like use the entire 20mm since the first 10 is already pretty much shot. It is hard to find an existing stud with the specific dimensions to fit. Easy if I ignore having the smooth section in the middle. Does that part really matter? does it just help center the manifold ? Any other thoughts would be greatly appreciated. Worst case I can redrill an tap a 10mm stud into that one whole (with an 8mm exterior stud), but would like to avoid that if I could.

Thanks

[18Fiatsandcounting]

The simplest solution would be to replace that one stud with a regular bolt, with a length so that you can make use of all of the threads in the head. If you want a stud, a place like McMaster-Carr likely has what you need. Look for "setup stud" in the section on metric threaded rods and studs.

Other less appealing options (to me) are to use a mild threadlocker to keep the stud in place even if you can't get it fully tight, or to drill out the hole and tap it for the next size up, which might even be an SAE thread.

I couldn't tell for sure which stud you were talking about, but of the five studs, the uppermost two (numbers 2 and 4) lead into an oil pooling area in the head so you'd need a thread sealant on those anyway.

-Bryan

[unplugged]

Thanks for the suggestions.
I decided I am going to try a helicoil to repair the threads and then go with some new ARP studs.
Hopefully that will work out ok.

[18Fiatsandcounting]

Thanks for the suggestions.
I decided I am going to try a helicoil to repair the threads and then go with some new ARP studs.
Hopefully that will work out ok.

That should work. Do you figure you'll have to remove the head to do the helicoil repair? I've heard of it being done with the head in place, but I think that's above my skill level.

-Bryan

[Nut124]

If you think you have 10mm of thread left at the bottom of the hole, then I would try to use it before trying helicoil.

Just get 8mm bolt with a long threaded section. Cut it to length and cut a slot in the end with hack saw so you can turn it with a screw driver. The unthreaded section of a stud just makes it so that the protruding length is the uniform regardless of how deep the hole thread was cut.

[unplugged]

Thanks for the suggestions.
I ended up putting in a Helicoil. I incrementally increased the drill size 1 step at a time to decrease the chance of drilling the hole crooked.
Taping straight was the hardest part. It was hard to get it straight and because of where it is, you can't see it from the side.
I reinserted the old studs in the other holes to use a references and used my cell camera to take side pictures to check it.
I then replaced the studs with ARP 8x1.2mm versions with 12.5mm thread depth. A bit overkill maybe but it is now very solid.