So I'm doing a top end rebuild and the blaster I have has been bored out so I'm not sure of the piston size. The piston has 125 stamped on top. Which makes no sense to me in inches, mm, or anywhere on the web can I find what size this correlates to. Any ideas?

 

stock displacement on a blaster is 196cc(they say 200)but actual is 196cc its stamped on the left side of the jug.the stock bore is equal to 66mm. so the piston u have i am assuming is .125 over but i would measure in with an inside micrometers. before u order a new piston.make sure u hone or have some one hone the cylinder to brake the glaze.

 

could it be the weight of the piston?

 

no..i have been working on bikes for a long time and have never seen the piston weight scribed on it...99.9% sure that it is meaning that it is .125 over bore.if you have like a harbor freight or northern tool.(cheep tool stores sells knock off and reman tools) get your self a cheap set of calipers and measure the i.d. of the cylinder.