Originally Posted by FarRider
A helicoil didnt work? Thats a new one on me, I've been useing them for years on full sized motorcycle engines with no problems, but ok, no biggie.
There are 2 options as i see it-
#1- drill and tap it out to the next larger size CAREFULLY!
#2- remove the cylinder, have the hole welded up and then drilled and re tapped for new studs.
If you choose to go the next over sized route be careful not to drill to deep or at a bad angle it might breech the exhaust port or the cylinder its self or even crack the barrel altogether.
At this point? id say screw it and buy a new cylinder, piston and rings from a reputeable dealer.
But thats me.
Drilling the exhaust stud hole won't breach the exhaust port. If you drill a STRAIGHT hole, the drill will breach into the cylinder stud hole. Drill all the way through to the cylinder stud hole (only to the hole), tap for stud (I would use a regular tap followed by a bottom tap), and replace the exhaust stud after the cylinder is installed and torqued. The replacement stud will use the cylinder stud as the bottom of the hole.
Here is a jig I made out of 2 X 4's
The cut away are for 6mm screws to screw into the head to secure it when drilling.
There are 3 mounting holes. This enables to drill either the exhaust or intake holes. The head can be flipped over and rotated 180 degrees. I don't remember the angle of the jig, but set head on the intake, and measure the exhaust angle.