oil tank threads, re-cutting threads?

I heard these are not normal thread sizes like pipe so not sure what would be used as the cutter. Maybe install an aluminum cap and then apply heat to it from a torch and melt the threads a little deeper??

I've used Dano's insert. Quality piece but I found the cap was very finicky and seemed to jump threads real easy. I calipered the cap in a few spots and it was not round either.

I put the cap on the bench and gently used a propane torch to make it round, then installed it again and seemed like it wanted to jump threads and become oblong.

I put a large hose clamp around the cap to help keep it round and it's worked well for me so far, one season. In doing this, I removed Dano's insert to allow the cap to screw on a tad further.

Can you remove the O-Ring on the insert to allow the cap to screw on further?

not a normal thread, not going to find die to fix thread but a thread repair tool might work but it will cost more than a new tank

dont get ANY plastic bits in tank...they could plug oil hole