Extract exhaust bolt: weld nut or drill?

[Boogle]

Hi guys,

Removed my exhaust manifolds from my 2000 986 2.7. Despite liberal use of care, time, penetrating fluid, heat, etc, I managed to break off 4 of the bolts. All are sticking out 3-5mm from the surface.

My question is, should I try the weld on nut technique first, or go straight to drill-out with a jig/kit?

I’d like to try the welding method, as there’s a chance of getting 1 or 2 out with little time spent, but I am worried about warping the head or something. Can I do this with a stick welder, or would MIG or gasless MIG be less risky?

I’m of course planning to take it easy - attach the nut, let it cool, build up some more weld in the nut, cool, etc. But, the whole point is you get at least some good heat in the stud/head, else it won’t work. The “MAP” gas I’ve been using obviously was not getting things hot enough to break the bond between rusty stud and head.

[theiceman]

if there are 3-5 mm of thread that should be enough to screw a nut on ... a couple threads.. if that is the case i would DEFINITELY weld. The heat alone from welding the nut on would help too ... i drill as a last resort . cant speak to stick vs TIG , it depends what you have on hand i guess

[Boogle]

Originally Posted by theiceman

if there are 3-5 mm of thread that should be enough to screw a nut on ... a couple threads.. if that is the case i would DEFINITELY weld. The heat alone from welding the nut on would help too ... i drill as a last resort . cant speak to stick vs TIG , it depends what you have on hand i guess

Thanks! Yeah, they are pretty rusty, but there’s enough thread left to even screw a nut on a little bit to keep it in place.

Still worried about welding just being too hot and there being a danger of warping the head. Hoping to hear that this is not a big risk if I take it easy from someone that has been through this with an M96 engine. Have you, Iceman?

I have found quite a lot on the net of people drilling out with jigs on M96, but not much about the weld method. Wondering why.

[theiceman]

Originally Posted by Boogle

Thanks! Yeah, they are pretty rusty, but there’s enough thread left to even screw a nut on a little bit to keep it in place.

Still worried about welding just being too hot and there being a danger of warping the head. Hoping to hear that this is not a big risk if I take it easy from someone that has been through this with an M96 engine. Have you, Iceman?

I have found quite a lot on the net of people drilling out with jigs on M96, but not much about the weld method. Wondering why.

not on an M96 engine. but given the heat an exhaust manifold puts out . i wouldn't hesitate to do it , but i get it, everyone's risk tolerance is different.

good advice above.

[elgyqc]

I can't help with the idea of welding... but I have drilled out several broken bolts and installed helicoils. With a good bit it goes pretty quickly. I didn't use a jig so some of my holes were a little off but no big problem. I installed stainless steel studs with bronze nuts so the next time it will be a breeze.

[S50Sinner]

Arc-welding shouldn't transfer that much heat to the head if you just weld one tack at a time. You can get a spot-weld with decent penetration and cause no damage, as long as you let it cool down between welds. Don't go all the way around in one go, and you'll be fine.

Higher amperage should work better, as the faster you melt them, the less heat will pass through to the head.

[Boogle]

Originally Posted by S50Sinner

Arc-welding shouldn't transfer that much heat to the head if you just weld one tack at a time. You can get a spot-weld with decent penetration and cause no damage, as long as you let it cool down between welds. Don't go all the way around in one go, and you'll be fine.

Higher amperage should work better, as the faster you melt them, the less heat will pass through to the head.

Thanks for the advice - makes sense. Will try to follow it!

[maxbottomtime]

Originally Posted by Boogle

Thanks for the advice - makes sense. Will try to follow it!

You ever sort this? I had 6 of 12 broken on a new to me engine. I tried welding, but the bolt just kept snapping below the welded nut, and had to buy the pricey jig to drill it out. I think the welding effectively heat treated it. Tungsten carbide bits were the key.