Exhaust port repair

Lock wire is also your best friend.
A reel of stainless steel lock wire and proper twisting pliers

Fast Eddie said:

@baz … how did your thread repair work out in the end ?

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I only tried it out on a scrap cylinder head so I haven't used it in anger
I have two heads to do when time allows and I'll report back with good bad or ugly results

I prefer to ensure the roses are tight.
With lock wire, the rose will not come completely undone, but could allow the rose to be slightly loose, fretting away at the threads.

If the lock wire is applied correctly there is no way it can loosen.
Tighten the rose with the engine hot and running. Locate a point tangentially to a rose fin, then apply the lock wire through a hole in the rose fin. Twist the wire from your anchor point or slightly close to the rose, as it twists it will shorten. Pass the wire through the anchor point and twist from about 20mm beyond. As the wire twists it will put tension on the rose ensuring it stays tight. Finally snip the ends at the final twist and bend the twist in half to leave a smooth end

Better than just static lock wiring. Live loaded after tightening. Allows you to remove and refit without using any lockwire or lockwire pliers. Never had any come loose.

That would work but I'd do it more neatly, maybe replace the wire loops with "S" hooks bent up from 3mm stainless steel wire hooked between the spring and hole in rose fin

As to the welded in repair. The new threaded section should not be straight through, but have a seat on the bottom. The pipe would but up against the insert and not the head itself. This would stop the pressure of the tightened exhaust nut from pushing the insert out of the head.
Not an original idea to me, but read about it on this site.

The problem is the design. Hundreds if not thousands have failed because the nut loosens and then the threads pound out. Redesign so the pipe slips in (add sleeve) and is held with a spring and the problem is solved forever. Screw the nut in tight till it bottoms out. Use high temp silicone bronze brazing rod on the sleeve and the spring catch. Seal threads and sleeve with high temp RTV and retighten nut when hot. Then forget about it.



BTW if the threads are just starting to fail you can expand the nut by machining plugs in .010" increments and press them through the Ex nut until the threads are a good fit again.

robs ss said:

This is probably a bit like an oil thread but...
I never use any compound on the threads - my rationale being if the lube helps it tighten, it'll also help it loosen.
I have a two foot length of pipe that fits nicely over the rose spanner. For final tightening I ensure the head is good and warm then apply tightening pressure with the engine running.
Vibes plus heat seems to work - they stay tight.
I also check for looseness (hot or cold) every month or so, just in case.

I never lube spark plugs either - same reason
Cheers

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Very good advice .