Tapping threads

[oomis]

I have 2 threaded holes in an exhaust can that connect it to the midpipe that are stripped. I'm going to tap them and use the next biggest size, so going from M6 to M8.

Do I need to drill the bolt holes first before tapping, to remove the existing threads? If so, is there a reference chart I can use so that I don't use a drill bit that's too big, which would remove too much of the material before tapping?

I'm hoping I can just use the M8 tap. The repair doesn't have to be pretty - it's on a track bike that's pretty ghetto already...

 

[VFR.CBR]

I have 2 threaded holes in an exhaust can that connect it to the midpipe that are stripped. I'm going to tap them and use the next biggest size, so going from M6 to M8.

Do I need to drill the bolt holes first before tapping, to remove the existing threads? If so, is there a reference chart I can use so that I don't use a drill bit that's too big, which would remove too much of the material before tapping?

I'm hoping I can just use the M8 tap. The repair doesn't have to be pretty - it's on a track bike that's pretty ghetto already...

Metric Tap Drills

You probably want to drill it out to 7mm.

 

[Tripletrouble]

With metric threads subtract the pitch from the diameter to get the tap drill size.

 

[Paulhv1]

Course thread, fine thread? 8mm tap is usually a 6.8mm drill

 

[meester_jamie]

if it is M8x1.25 you can use an H drill,, or 17/64 is 0.0004 smaller,,, so I use the 17/64 bit

 

[Acadian1974]

Or you could just install a helicoil