Is it OK to heli-coil an exhaust stud?

[911mot]

Ive been having major grief with one of my exhaust studs.
It broke becuse I didn't heat the nut so I center punched and drilled out the remains. Started OK with a 3mm pilot and the gradually went up .5mm in drill size till I could see the original thread. Great I thought, now I'll just clean it up with a thread restorer. I must have been rushing because I managed to snap it off in the head. Cue wrench being launched at high speed into garden. Next day I drilled out the broken bit and got to a similar stage as last time, only this time I tapped the hole with an M8 tap. Screwing the new stud in seemed OK at first but as soon as it 'bit' and I applied some torque it stripped the thread.
So what should I do now? Should I tap it slightly larger for a bigger stud, or will a heli-coil insert get me out of this one?
Thanks for your advice.

[john walker's workshop]

a helicoil or timesert should work fine. i like timeserts, personally.

[911mot]

OK thanks. I've already got the helicoil so I'll try it first and if I bugger that up, a timeserts it will be..

Just been out to look and realised (I think) my second mistake. I used an M8 tap. Shouldn't that have been an M8 x 1.25??

[john walker's workshop]

yes.

[911mot]

Me ---->

R.O.W-->

[ChrisBennet]

Originally posted by 911mot
OK thanks. I've already got the helicoil so I'll try it first and if I bugger that up, a timeserts it will be..

Just been out to look and realised (I think) my second mistake. I used an M8 tap. Shouldn't that have been an M8 x 1.25??

Am I missing something? It would be an unusual "M8" tap that wasn't M8x1.25. A Timesert will be a better solution. See if you can borrow someone's 8mm set.
-Chris

[snowman]

A helicoil is a lot cheeper, smaller than a time sert. If the installation succeeds, great. If not theres still space to drill it out more and put in a time sert.

I did an entire mag case with helicoils. There were a couple of spots where I had to use timeserts, because the helicoils failed, mostly due to operator error. But arn't 2 chances better than one?

[911mot]

It would be an unusual "M8" tap that wasn't M8x1.25.

That's what I thought. I just went and bought an M8 tap on its own.

But after the thread got damaged I looked for a tap and die set on the net and found they come in M8 and M8 x 1.25

FWW I can't screw a new barrel nut up the M8 tap. I'll try the 1.25 tomorrow when it arrives

[snowman]

If you are putting in a helicoil or timesert you will not be using a std tap. You need to be using the one for the helicoil or the timesert that accepts the 8 x1.25 mm stud.

See the helicoil or timesert tech info for correct sizes.

[1fastredsc]

Helicoil should be fine, ones i've had are all some really hard type of stainless steel, which i'm sure won't have any problems with the localized heat.