Buddy of mine asked me to replace the piston, rings, etc. on his '86 RM80. Can anyone give me instructions on how to do this? Thanks.

 

sure:

1. unbolt the 4 nuts holding the cyclinder to the case, and the 5, or so bolts on the head, where the plug goes in.
2. order a weisco oversize piston + rings, like .010 or .020 over.
3. bring it to shop and get it bored to match the pistion( make sure the chamfure the ports) bring the piston and assc, with you when you get it done
4. reassemble, put rings on piston, slide cyclinder on to piston, and bolt down, + bolt down head.
5. break the new motor in-dont rev it too high, nice and steady.

 

What he said, except if it is already bored out then go the next biggest bore.

 

Wash the cylinder with soapy water to get all the honing grit out after it is bored , and make sure you lube the cylinder with 2 stroke oil before you install the piston assembly to prevent metal to metal contact on startup. A dry start will reduce the life expectancy of the engine. Also make sure you point the arrow on the top of the piston to the exhaust side, it likely wont last long unless you do. Same goes for the head gasket if applicable.

 

thats all there is too it, just make sure your borer "chamfures the ports" thats a big deal on a 2 stroke

 

What does chamfure... mean?

Why can't we just put the same size piston in it? Does it have to be bored?

 

all chamfure means is cleaning up the ports on the cyclender after it is bored, when a engine has ware, the cyclined gets stightly out of round, so boreing it to the next size will remove those inperfections, and give it a true round area in side the cyclinder