Sump bolt thread restoration

[Ruairidh Dunford]

Do helicoils work for threads already tapped out to 5/16"? I've never used helicoils before.

For example, would these work?
https://nzsafetyblackwoods.co.nz/product...-20-457154

Sorry not to come back sooner, I have been away.

In theory, the answer should be no. However, over the last 30 years, I have probably fitted at least 100 1/4 bsw helicoils straight into 5/16 bsw sump holes.

To be absolutely certain that this is the case - I just went out into the workshop and fitted one into a bell housing stud hole of a crankcase I am working on. I can confirm the 1/4 bsw helicoil wound nicely into it and the 1/4 bsw sump bolt them wound into the newly fitted helicoil, as it should, using my finger and thumb.

I use 1/2 depth helicoils in this application.

If you wish to try this yourself, V-Coil thread inserts are reasonably priced, here at least.

[falcott]

Thanks for getting back, Ruairidh. The thread pitch is different for 5/16" and 1/4" -- 18 vs 20 threads per inch. You're saying that it doesn't make any difference over half an inch?

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I make a steel threaded insert from 3/8"BSF studding with a blind hole. I set it in the crankcase at the set height with Loctite. No more stripped threads. 

Nice work, Robert!

[Ruairidh Dunford]

As mentioned, I have always used half depth coils - these are nowhere near half an inch.

I am not sure what else I can offer you on this.

[falcott]

Ruairidh, I've bought a V-Coil kit based on your recommendation. Thanks.

[Ruairidh Dunford]

Do try to get 1/2 depth, these are 3-4 coils only.

If you cannot get these 1D are more commonly available.l and should be fine too.

[falcott]

Ruairidh, I ordered 1.5D, as it was the shortest that I could find locally. I guess that should work.

[Ruairidh Dunford]

It needs to be 1/2D or 1D.

[Ruairidh Dunford]

Hold the coil with long nose pliers and use the edge of a bench grind stone to remove one thread coil at a time.

If this does not make sense, ask, and I will photograph the process.

[falcott]

I guess it's cut from the top of the coil?

[Ruairidh Dunford]

Correct.