Those exhaust studs are probably 6mmI have a Schwinn stingray friz fifty and the exhaust bolts and the intake bolts keep coming loose, I put rubber never tried without it, I'm on my 3rd cliynder due to the screw holes getting stripped from coming out so much, any ideas?
If they stripped, (pulled out) just tap em to 1/4"x 20
1/4" x 20 is the next size bigger thread size
It's so close you wont event need to drill it first
Just tap the stripped hole
This is a common way to fix stripped 6mm threads in aluminum Motorcycle cases