The Gearbox drain plug hole on my old motorbike has stripped threads. The gearbox is Ally and the plug is steel. I need to repair and I guess there are a number of options.
1. Run new ally weld onto the old hole and then recut threads.
2. Recut the thread larger and get a larger plug
3. Helicoil insert down to original thread size.
Which do you think is the best/easiest solution. Is it true that a helicoil would not be suitable because oil would still leak? I've used them before but not in this sort of application.
Thanks,

The easiest option would be to redrill and tap to a larger size imo, but that depends on whether you have sufficient metal to take the larger thread.

I have no idea what helicoil is but i would think recutting a larger thread and getting a larger plug would be the easiest

A helicoil should not provoke a leak as the sealing happens between the compressed face of the plug and the flat face surrounding the tapped hole. Is there not a fibre/copper washer there?

Or there is another alternative........
Use a tapered thread plug.
Whatever is the best size for your hole (!!) and as long as there is enough maet around the hole.

I've repaired similar in the past using a BSPT (Tapered BSP) plug, after re-tapping of course. Minimises the risk of stripping again as there is no shoulder to over tighten against.

Another vote for a re-tap




Ronnie

I would tap oversize --- try BSP tapered

Any idea where I would get a BSP tapered plug? Are they easy to get hold of? Current plug is 1/2" I think.

Thanks for all the input

I once owned a ZX10 that had a parallel thread drain plug with a copper washer.
The copper washer had worn to a sort of cone shape. When I tightened it the coned washer caused the ally sump to split.
I still hear that metallic ping in my dreams.

For this reason I would not advise a tapered plug in ally.
I would use a straight thread and a NEW copper washer.


Paul G