Stripped Exhaust flange thread. Can it be repaired with a Helicoil?

[Ropariva]

When I recently put my exhaust system back on after the engine rebuild I was concerned one of the studs at the flange didn't have a lot of grip in the newly threaded hole. Unfortunately this proved to be the case and I have had to resort to a 3/8 bolt through, which just doesn't look that great.





My manifold had already seen some repairs over the years by the PO and some of the threads have had to be replaced with oversize studs purchased from XKs.






My question is can this be successfully repaired with a Helicoil? Ive used them before in alloy heads etc but never in a hot exhaust application
Many Thanks, Alan

[abowie]

I think that a helicoil would work fine.

I have used the oversized studs with success. The nice thing is that they are a coarse thread which I think is a better choice for the cast iron.

[PeterCrespin]

It may not look great but it looks 'OK'

If it's one of the oversize studs that has stripped then remember that to fit a helicoil you have to drill/tap larger again and there isn't a huge amount of meat on those corners (which may be even thinner from polishing). Cast iron is not very strong in tension and rather brittle. So you need to weigh up the risk of a snapped-off corner - which will happen far easier than on the lower steel flange - versus, say, purchase of a stainless button head socket screw to use in place of your hex bolt.

The finish looks very nice but I guess it means you can't just replace one manifold if a couple of over-tight corners snap in service.

[Bfastr]

I installed two of those "repair" studs from XKs myself. I just drilled and tapped the holes to the new size. they work like a champ.

after re-reading, I think I understand its one of those repair holes that has already stripped out again? if so I would do as Peter says, not sure I would drill an even larger hole in the corner.

[288gto]

Assuming it is one of the already oversize holes, you MIGHT be able to helicoil it back to original size without the risk that Peter mentions of removing too much material on that corner.

Simon

[Geoff Allam]

If that hole is already oversize my choice of repair would be to apply a layer of braze 360 degrees insode the hole then redrill and tap it to the original size.

[JagWaugh]

If that hole is already oversize my choice of repair would be to apply a layer of braze 360 degrees insode the hole then redrill and tap it to the original size.

Silicon Bronze MIG wire works well for this too. You do need to preheat and cool slowly.

[cdaubs]

Alan,

Great looking manifolds! Are they ground and polished or are they coated? If they are coated, what product/service did you use?

Thanks,

Charlie

[Ropariva]

Hi Charlie, yes, the original manifolds were filed, linished and polished prior to a Ceracoat ceramic process inside and out. Very long lasting. Still looks great 3000 miles later.