My muffler came loose on my YS 63fz and I am concerned the thread on the engine may be slightly dinged. What is the size/thread of the muffler header?

11x.75mm. We have taps available if you can't find them.

I may need one and a new threaded header. How can I contact you?

775-265-7523 weekdays 8 to 5 west coast time.

Dave
I installed the new threader coupler/header with teflon tape and it still fell out so I think the engines thread are damaged. IF I buy the tap to chase the threads do I have to disassmble the engine?

Just make sure the exhaust valve stays closed while cleaning it out and you will be OK.

IS there a simple way to make sure that it is?

Take the plug out and put the piston at TDC