Optimal Piston to Cylinder clearence measurement?

[yz250flash]

This is for a 1996 200.

I know the manual gives a range of 0.079 - 0.089 mm but I have read on a couple of post that people are running tighter tolerances than this. What are you guys running if not going by the manuals specs?

I had my cylinder re-measured this morning and came up with a measurement of 66.04 top and bottom, side to side (so it is still round). What would be the best piston size for me?

Using the manual's tolerances if I went with a "C" piston (65.96mm) I would be at the lower range of 0.080.

My cylinder is actually a "B" but if I used that piston (65.95mm) then I would be at the top of the tolerance.

Here is a list of the piston sizes from Pro-x and Wiseco:
Pro-X:
A = 65.940 mm
B = 65.950
C = 65.960
D = 65.970

Wisco: One standard size of 66.000 mm

Your help and advice is appreciated.

 

[bikepilot]

I like to run them on the tight end, just take care when warming up as it will be easier to cold seize. If its a loaner bike that is likely to be abused run it on the loose end, if its yours and you properly warm it up running it on the tight end will give slightly less piston slap noise, more compression (very little difference here) and should last slightly longer.

good luck

 

[Jackpiner57]

I just did a top end job and Wiseco specifies .002 clearance. It worked well for me. :nod:

 

[yz250flash]

Hmmm....002 equates to about .05 mm. That's pretty tight. With that tolerance I could actually run a "D" piston in my "B" cylinder. I want to reduce the piston slap but I don't want to get it so close as to seize it easily.

Anyone running a Pro-X with this amount of clearance?