Lightly buff the top of the piston,if it's an over size should show on the opposite side of the stamped marks. Would show a .25 (.010) or .50 (.020) on a Polaris piston. I believer the 5W is a stock piston. Have the cylinder measured before you order a piston kit! Standard bore is 72mm. You can get piston kits all the the way up to 74mm! You don't need to take anymore metal from the cylinder liner than necessary to clean up the bore. OPT

 

its is a stock piston im looking for just the rings now cause i believe the piston is in good shape, the piston number is 3083942 and the rings im looking for is 3083546 im having a hard time finding the rings, the rings i found are for a 488cc can i use those on my 250? i need two rings also.

 

piston only says F and 5W no other marks, i looked it up 5W is stock

 

After 5 pages of posts have you done a compression test yet ??????? You can't just throw rings on a two stroke just because the piston looks good!! You have to measure the clearance of the piston to the cylinder. If you're going to take the cylinder off anyway,just have it ACCURATELY measured as to where you can reuse the existing piston(if stock,highly unlikely) or if it needs to be bored out to the next oversize or larger to clean up the bore. These engines are not like car engines to where you can just "re ring em" OPT

 

and why cant i just put rings on piston????????

 

it is a stock piston for sure and cylinder is in good shape just the rings were shot

 

BUT have you measured the clearance of the piston skirt to the bottom of the cylinder?? If it's .004 or more you're just wasting money on rings,especially on a stock piston on a 15 year old machine!!Talk to any cycle shop on 2 strokes. OPT

 

it is all taking apart so how do i measure lol

 

i am wondering how to check my timing and wondering why its back firing out the carb when trying to start, it will not fire up at all thanks

 

Timing is set electronically by the cdi(replaces the old points and condenser) Back firing out of the carb usually is from low compression on two strokes,fuel can't atomize well,will pop back through the carb when it occasionally tries to fire . OPT