On our 24 roadster's exhaust manifold there is a 1/8 inch hole by the #1 cylinder that shoots upward and I would like to try to fix it with J-B weld so that I don't have to take the manifold off the engine. Has anyone tried this and been successful.

I have on other vehicles and it has been sucessful both times. Clean it good, it works great.

J-B ain't gonna cut it.Furnace cement might.You can also try a small sheet metal screw.Try threading it into the hole.A little furnace cement might help.I did this on a tractor for which no new manifolds were available[then]and every used one holes.

You can braze it .

Its not hard to straighten a manifold with the right stuff. If there is a club in you area they might have it.

Jack, as a rule bronze doesn't work very well on exhaust systems. When it gets hot it softens up. Much better to weld it. Dave

I am unclear if this is a warpage issue or a rust hole.Attempting to weld a rusty manifold that is thin enough to have holes is probably a waste of effort.

I brazed an exhaust manifold together many years ago and itis still there.

I would agree with jack I have lots of exhaust manifolds repaired with brazing, used, and obviously still working. Its so easy to pull the exhaust manifold by using a half clamp and leaving the intake on.

But the exhaust is almost always bent down at each end so the only way to repair is straighten them.