Do I have the right piston??

[Z0RR0]

Hi all,

Well, I rebuilt my engine from top to bottom, and have one problem.
My old piston seems to be from the same manufacturer as the new one (OEM, and reads "ART" on the inside), but the old one has a little 1 with an arrow pointing up, while the new one has a 2 with the same arrow.
What do these figures mean? Do they represent a batch, or model, or size, or ... ???
I measured both, and the old one is (not surprisingly) slightly smaller than the new one. Would it be a wear issue, or could the old one be "undersize" (I did order a non-oversize piston)? But I don't have the right piston or cylinder tool neither. I can't remember the exact figures off hand, but I could re-measure and post 'em if it could help someone to help me out...

The bike is a TMR modded Honda CR 250, so I'm quite unsure of what's inside since I bough it used last summer.

Anyways, worst case scenario, I wait until next monday and have a dealer make sure the piston and cylinder match ... :| ... but I really was looking forward to riding this weekend...

Thx in advance for any help

 

[BJAWES]

Are you measuring the piston with a micrometer? Do you have an inside micrometer to measure the cylinder? Just how different in size are they? Even 30 thousenth's (.0030) is hard to see with a tape measure. I think you're back to the dealer or machine shop for some cylinder and piston matching/measuring. If you bought it used it may have been bored and then sleeved or just bored? Who knows? I think worst case scenario would be finding a piston to match that of your orig. if it is indeed a different size than OEM. Sorry. bjawes

 

[Z0RR0]

Of course, I measured with something else than a measuring tape ... did I really sound like such a :joke: ? lol

With a micrometer, I measured a dia. of 66.33mm. Assuming the cylinder bore is stock, is that ok? I guess it is... but would really like to be sure ... lol

 

[SX85]

gtrsd

when cylinders are casted in the factory not every cylinder comes out the same size so pistons with a #1 mean they r a size 1 if it says 2 on it the piston is a size 2 the 2 is ussually bigger than the 1 by a very small amount so for they cylinder sizing difference if the cylinder is a little big its a 2 and if its just rite its a 1