Sump bolt thread restoration

[falcott]

Hi all,
I'm wondering if it's possible to restore the 1/4" threads in the crankcase back from the 5/16" threads that it is currently? I'm thinking of fitting an ally sump, and it will be a shame to drill it out to 5/16. 
Or would it be better to change the crankcase?
Ta.

[Ruairidh Dunford]

Fit helicoils.

[falcott]

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

[Ian Williams]

No they don't, if the case is already out to 5/16 or above I use bespoke brass or aluminium inserts to plug the holes if the case

[falcott]

Ah, okay. I'll look at getting some plugs made up, I guess. It could be an engine-out job.

[bystander]

How about converting to stepped studs, 5/16" down to 1/4"? That would save an engine out job.

[falcott]

How about converting to stepped studs, 5/16" down to 1/4"? That would save an engine out job.

Good point! I never thought of that. Thanks.

[Ian Williams]

Studs will work although they can make sump removal in-situ difficult. I would not recommend undertaking any of this work without removing the engine first.

[falcott]

Studs will work although they can make sump removal in-situ difficult. I would not recommend undertaking any of this work without removing the engine first.

Hmmm... it does make sense. I'm inclined to plug the holes with brass inserts and start again, then use cap screws and fibre washers.

[Robert Foreman]

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.