When removing the nuts from exhaust studs from one of my cylinder heads, the entire stud came out - which I have seen several times before. What I have not seen before however is that one stud was in a helicoil that was pulled out. In the process of the helicoil pulling out, the threads were destroyed (see pic).

I have a friend that is a professional welder that I'm hoping can fill (weld) this hole back up with aluminum, then drill & tap a new hole. Does anyone see any issues with my plan? Is my head a goner?

I have a 2L head with a loose thread and may need the same work.

If you can actually find a welder good enough to fill the hole, then thats the way to go.
You dont have much meat there to work with.
IF he can get it filled, I would pay a machinist to drill the new hole.
Take the studs and the exhaust with you to make sure they line up.
You would be very pissed to get it all back together to find out you cannot get the HEs on.

You didn't say what you were doing to the car--but the head will need to come off to properly weld that up and machine it. The heat will most likely cause the aluminum to move around a bit, so you'll probably need the seats replaced or at least re-cut.

Might as well have the head rebuilt while you're at it... And the other as well, of course. Maybe send them to HAM if they're 2.0 liter heads? If not, consider getting a pair of the aftermarket AMC heads and having them gone through.

--DD

What Dave said ...

The Cap'n

Sorry about that, I should have been more specific. I am doing a complete rebuild on the engine, so the heads are off. After I get the welding done, I will have them checked out. They are 2.0L heads as well.

The welding should be done by the shop doing the heads. If they can't do it, you've chosen the wrong head repair shop. It's more common than not to have cracks in the exhaust port that contribute to the pulled studs, and the welding job is likely to extend far beyond the actual boss. HAM, CE, EMS and a few other shops here in the US are qualified to do T4 head work, and going to a shop right down the block or right across town because it is close by is usually a mistake. The big brown truck makes everything local!

The Cap'n

Is there enough meat there to Timesert it?

re+re the valve seats,check for cracks,remove the guides before welding.
A ceramic filled adhesive may work here after pinning the stud into place.
The TIG method is of course #1.

Timeserts require the same amount of parent material as Helicoils. In fact, they both use the same tap. The question here, as has been pointed out earlier, is the integrity of the head. Most often this damage is a result of cracking, which can include the ports, seats, and spark plug holes. Just installing the timesert can open up the cracks, and torquing down the fastener in a helicoil can expand the coil enough to do the same.

The Cap'n

True that! my plug threads were "repaired" with thread inserts. Cracked the combustion chambers around the inserts like an egg in no time at all .Please post If you find someone to rebuild your heads, I'm in the same boat myself.

+100 on this. Don't waste another second thinking about how to fix this exhaust stud, get your heads checked out to see if they are worth rebuilding/reusing, and if this is repairable.

What about the stepped exhaust stud. One end is still M8-1.25 but the other end is oversized so you have more surface area. Of course if the heads are not rebuild able then it is a mute point. All of my exhaust studs are the stepped oversize variety.

David

Good option; you should be able to get custom studs made with whatever oversize on one end you need. With a lathe i could see starting with a say 12mm bolt and machining down one end to the 8mm size and then running an M8-1.25 die over it.
Then drill & tap the head for the 12 mm thread.

Someone makes these special studs. I have seen them somewhere.

At 12mm you're gonna have a wall thickness just barely enough to hold that stud in a strong crosswind ...

The Cap'n

I would like to offer my personal opinion on this.

A master welder may not be a great machinist.
A great machinist may never weld.

I have had good experience splitting up certain types of repairs with this in mind.
It does not work all the time, but it may in this case.

rich

Flat out BS. Talkin shit.

The 3 places I mentioned do both as well as anyone could, and they know how and where the cracks form and how to repair them. And, better yet, when NOT to pursue repairs.

The Cap'n

I know HAM is hoffman automotive machine, but what is CE and EMS?

Competition Engineering
Engine Machine Service

EMS is European Motorworks who also does type4 machining.