ChitownRC

I was looking for back plates for the os 18 tm b/c i just bought a bump start and 40mm flywheel. Do you have to shave off the crank shaft nubby to put the back plate on?

Yes you do. RD makes a backplate and the non-ps backplate from a OS CV-R will fit also.

Going to have to take the motor apart?

yup

Yeah man, you dont want those shavings floating around in there. Take it apart, grind that thing down and make sure you clean it good. Seal up the carb and backplate good also.