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.