FH Dry build - primary case

One of the problems you always come across when tinkering with unloved old bikes is broken screws. The Huntmaster hasn't had many, but while I am working on the dry build it is time to fix these kind of problems as we come across them.

This is a typical example - a broken 1/4" BSW screw in the primary chain case. Of course, it is too short to get hold of and Plus Gas has no effect on loosening it enough so that the little bit I can get hold of can help it come free.

The only sensible option is to drill it out and and re-tap the thread. I set the inner case up on the pillar drill and used a centre drill to start the hole, opening it progressively (0.5 mm increments) to tapping size, hoping to release the remains of the screw.

This didn't work out, and after attempting to chase the rest of the bolt out with a tap, for the first time in my life I managed to break a tap in the hole. I spent the rest of the evening laboriously grind it out with a diamond coated tool in the Dremel.

Once I had removed the tap, the next step was to drill out the mess for a Helicoil:

Then tap for the Helicoil:

Then screw in the insert. You break off the tang used to put the insert in when you are done: