How to see if cylinder has been bored out?

[TheSlacker]

I have a 1995 CR250 that I bought last year. I'm looking to rebuild the top end, but am not sure if the engine is stock bore. Is there any serial numbers on the piston that will tell me if it is stock bore, or is an oversize piston?

Thanks

 

[oilspot]

is there a harbor frieght close to where you live? If so go buy some dial calipers. The cheap ($14) ones will work just fine. You can measure your piston diameter with them.
You can get nicer calipers... but for rough dirty work cheap ones get the job done just fine.

 

[76GMC1500]

The crown of the piston will usually have the size stamped in it. It may say nothing or STD if standard. If bored, it will usually be marked .25, .5, 1.0 etc... indicating how many mm oversized the piston is. Generally, 2-strokes made after the mid-80's do not get bored because they have plated cylinders. Depending on the quality of customer service, your local shop may mic your cylinder for you at no charge, especially if you buy your piston from them. My closest shop would never do this, but I drive to one 20 miles away to another shop and they are more than willing to help me out with any questions I have and any quick tasks I may have.

 

[john stu]

the 95 cr250 came stock with a plated bore...........just to let you know ,but who knows if its stock you will have to take it apart and see

 

[TheSlacker]

Thanks. I didn't think it would be bored out because of the Nikasil (or whatever they call it) plating, but want to be certain before I start ordering parts.

 

[oilspot]

I may be wrong about this. But I was under the impression that even standard pistons came in an a,b,c, and d size. I do know that you need to take measurements to insure the correct piston/ cylinder clearance.
I wouldn't want to assume that I had the right piston. I could see that ending up costing a lost of extra money.
Of course to measure the bore of the cylinder, the calipers are not going to be good enough.

 

[griffbones]

I agree with oilspot!
This is what concerns me about buying a Wiseco piston for use in an oem cylinder of stock bore. What if their supplied piston is slightly over or under sized and the cylinder is slightly under or oversized, things aren't always perfect to specs? I know Wiseco makes great pistons but they don't offer A,B,C etc....
I have been thinking about this for reasons of maintenance on my son's 2007 KX100 engine, it is new now, but will need freshened up soon enough.