how will i know what size piston i need?

[2-strokes-4-life]

if nothing else gets in the way i hopefully will get this bike rebuilt soon.anyway,when i pull the cylinder what do i have to do to figure out what size piston i will need?if i will need measuring equipment,what will i need and what kind of price range can i expect to pay?i dont have alot to spend so would it be cheaper to have it measured by a shop?anybody have any opinions on what piston i should go with?im looking at wiesco or vertex.my buddy that i bought the bike from said he always stuck with vertex which is whats in the bike now.just would like to maybe hear others opinions befor i decide.also if i will need it any resources of where to buy the measuring tools?thanks in advance for any input.oh yeah my 01 cr125 is the one getting the top end done.

 

[WillyM]

The dial bore guage can cost $150-$400 I would take it to the shop who is going to do the bore and have them measure it then order the piston that you need,then bore it when they get it.

 

[NO HAND]

If you feel ready to replace the piston yourself you may want to study your owner's manual before starting to tear the bike down. It's worth it because the knowledge you gain will be helpful also for the next top end job. More likely you will need a stock bore replacement, I personnaly prefer Wiseco because the composition of a forged piston is a bit stronger than a cast one. Open the cylinder first to make sure there are no bad surprises in there and go to the dealer order a piston for the stock bore. If the cylinder is fine, there is little need to measure. Just go ahead and buy a piston. By the way, there are no iron sleeves anymore in a cr125 so you cannot just rebore to the next size like we used to.

 

[WillyM]

oh I thought that you had a sleve in your bike.

 

[2-strokes-4-life]

thanks for your replys,when i pull the cylinder is there anything particular i should look for to know if it is acceptable to just replace the piston?i spoke with my friend who i bought the bike from awhile ago and he said something about that vertex makes pistons in slightly larger sizes to compensate for cylinder wear?if i order the standard size,is there a way to tell without measuring it if the tolerances are within spec?just didn't want to end up ordering the wrong size and have to go through the hassle of having to exchange it.anymore advice would be appreciated thanks

 

[NO HAND]

Well the Wiseco expands when heated and there is only one size so choosing the right piston is fairly easy. When you pull out the cylinder, look for scratches or sings that the plating may be damaged. Look also at the bridge in the exhaust port, the plating there has a tendency to crack because Honda was lazy on bridge tolerances in those years.