tore the trailboss 250 down this afternoon. everything went as well as expected. exhaust was a little hard to break loose. after getting it all apart, i ended up breaking one of the head studs off while removing. ended up drilling and am going to install a thread insert. only small question i have is- as far as i know, stock bore is 72mm. i measure the piston and cylinder and read 72mm, but the piston has a marking of 5w on the top. does anyone recognize this marking? seems like if it stood for .50 over, i would have a much larger reading on the bore and piston. any advise? it is going to the machine shop and i will let him measure too.

 

Mic the piston then measure the piston to cylinder clearance.Then go the next size to get .002 clearance.

 

took the cylinder to the shop monday. he measured stock bore also. he called tuesday morning with great news-all done. picked everything up and had her fired up in a couple of hours. what a differance. starts right up(no extended cranking or playing with choke). it idles!!!!! down pouring rain and cold, so no test drive. may take it out wednesday.