I had a exhaust stud on my 360 "J" headed motor start leaking. Well long story short the exhaust holes are heli-coiled and I can't get a new heli-coil to "hold" in the head. Re-tapped, new coil with rtv & let setup for a couple days. Install header stud. All seems well till I try to torque down nut. The heli-coil keeps pulling out of the head. Ran the tap in further and got some 1" long coils from McMaster Carr. Same damn thing. I know the threads in the head must be too rounded over to hold the coil in. Question: What is the best epoxy to use here? High temp area that needs to seal from coolant as well.

This is my last attempt before ripping the top end apart. Any ideas would be great.

Next time you have the head off install these. My local Ace Hardware stocks and sells them. For now JB weld will probably bandage it for you. Its not good for in the port but should be high enough temp for that repair. May not be the right size for you but just an example.


http://www.mscdirect.com/product/details/97435796

Rather than a helicoil find some of the solid thread inserts and epoxy that in there. That should fix it for good.

Wasn't aware of these solid inserts. That's great to know for next time. Appears to be much stronger.

Can you go up a size in a metric?

The best fix is to pull the head and make an oversized (and solid) insert. It requires a lathe to thread the OD but it's relatively easy. I will also say in a pinch I have taken the next over size (you may have to go two sizes over) of bolt, drill and tap the existing hole to the appropriate size and screw the bolt in with a quality sealer. Cut the bolt head off and grind/file it flush. Lay out the center of the hole with the gasket (or lay it out by math...they don't have to be THAT close but you can lay it out) and drill and tap the bolt to the correct size.

I would never try these on the car. But it's a clean fix.

In you example, since you have the helicoil already in, you would use a 7/16 bolt to start with. That will get you out far enough from the helicoil thread (IIRC the size of tap for a 5/16 bolt).

There are some inserts that I have never seen or used that do the same thing as I said with the bolt. I don't remember the brand name, but by the time you bought the kit, you could do the same thing with a bolt.

Some really good thoughts. Never thought of possibly metric. There's about 3/8" at the front of the hole that's already larger with no threads. Will have to mic it and see where I'm at. Maybe I can drill from the wheel well to size it for a new tap.

If I do epoxy in a heli-coil as planned, is there any "killer" high temp epoxy that would be a better choice than JB weld, although I do have that in stock.

Keyserts (Keenserts) is probably gonna be your best bet to try and fix it in place. You can find them on line or at your local parts store - maybe. They are like a thick walled helicoil. After you thread them in, you drive in 4 pins to hold them in place - rotational speaking. I have used them before in your application with success.

I used these to fix a leaking header bolt in a pair of 906 heads on my dad's 6 pack car. That was about 5 years ago and no problems.

Best fix for this is to drill and tap the head to a pipe size. The taper pipe will seal on the outside, and give you fresh material to drill and tap to the correct thread size.

I guess the question is that if I have to drill out for an insert, can the hole accommodate up to 9/16" thread without ruining the head? For reference it's the 2nd bolt in.

You can get then in a smaller outer diameter and the larger outer dia, I have used them for years in the aerospace industry and they work quite well.

Problem is they wont seal water. Go with the pipe plug.

Don't waste your time , Heli coils get threaded into the hole , the hole is slightly undersize so the coil grabs and form the proper size thread for the screw you are going to install to be able to be torqued.It sounds like your threaded hole is already too big and that is why the helicoil won't allow you to tighten the nut on the stud.

go to vatozone , they will have a high temp epoxy that you can fill the hole with , but I think your best bet is to go up to 7/16 thread and put in a keensert.

Put them in with epoxy and they will seal. I do like your idea also.