Question on Top End

[gthoma23]

This is the first time i've torn down my top end on ’03 CR250 (bought it 9 months ago), so i got a few questions. and i'm goin off what the service manual said, so i hope it's right.

it says the recommended piston ring gap should be .4 -.55mm with a service limit of .65mm. it says to take them off the piston, and push them an inch into the bottom of the cylinder and measure the ring gap. my question is, what does it mean if it's less that the recommended gap? I measured mine, and there around .175mm. does that mean I need to replace them, or did the guy that owned it before me put them in wrong, or can I just file them down and be good?

Also, the manual says that the piston and cylinder should have either an A or B on them. I looked, the cylinder has an A, but the piston doesn’t have either, just some numbers. So I’m guessin it’s aftermarket, is there a way to tell what kind it is?

Thanks fellas!!!

 

[steve.emma]

as it happens im in the middle of doing a top end job on my 02' cr250 so maybe i can be of some help......
the honda pistons are either an A or B as you know, but if its a wiseco or pro-x tye piston then they make just the one standard size for the 02'-04' cr250's. the actual difference between a A and B piston is pretty small anyway (if you do a search on here you will find a post that tells you that difference).
wiesco pistons normally have a part stamped onto the top of them.
are you sure you measured the ring gap properly? as that end gap sounds very small. did you use the piston to push the rings into the cylinder evenly? otherwise you wont get a correct reading. re-gap them to the factory spec if that reading was correct or the rings could cause it to seize when the engine gets hot.

 

[whenfoxforks-ruled]

File the rings to with in spec. Check that the skirt to bore clearance is proper. And finally check the skirt to exhaust bridge clearance.

 

[gthoma23]

I found out i have a wiseco piston std. and i was lookin on their site, cause i read that forged pistons have different specs than cast/stock. and i found what the ring gap is pose to be. on top ring is 0.265mm and the bottom is 0.33147mm. that is still over what mine are at now, but still a lot smaller than the oem at .40-.55mm.

so since it's forged, does any one know the other specs for the wiseco piston? like the cylinder to piston clearance, and the piston o.d.?

Thanks!

 

[steve.emma]

sorry gthoma23 i dont know those specs you are after but if you have the service manual i would just go with whatever is in there. i dont think it would be any different for a wiseco piston than a standard piston, but i could be wrong on that. maybe a question for Eric or Rich.
while on the subject for clearances for a minute do you or anyone else reading this know what the conrod big end side clearance should be? i just checked mine and ive got .80mm which seems a tad big to me...... i hope its not as i really dont want to have to do the bottom end as well. :(