Maintenance & Technical > KX250 / KX125

'89 KX250 Project

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keithluneau:
That and the powervavles not working are probably both to blame!  :|

This is quickly turning into a fun project though. I like working on these. I just wish I could have got some riding in! I'm dying to ride this one, it's the first two-stroke bike I've had...  :-D

Jopiz:
How much does a steel sleeve affect on power output? Is the difference significant compared to a nikasil cylinder?  :|

KXcam22:
Jopiz,
 As a teen I used to race a rotary valve KX125. Very fast but had a chrome bore (not nikasil) and they would eventually chip.  In those days no-one could replate so a steel sleeve was the only fix.  No matter how well we matched the ports the bike was always slower than before.  The only thing I could attribute it to was the higher friction of the steel liner. Cam.

Hillclimb#42:
 I believe that the steel sleeve requires a looser tolerance than with nicasil. I'm pretty sure that I read that on here. Since the sleeve is iron and the piston is aluminum, they expand at different rates and to different amounts. Stock cylinder is the way to go. Can a stock nicasil sleeve be put in there, or is it toast once you put an iron sleeve in it?
You're definately getting the crash course in engine service.  :-D

KXcam22:
I had forgotten about the greater piston clearance required. The nikasil can run a tighter tolerance since it essentially is a thin hard coating over the base aluminum cylinder and so expands and contracts at the same rate as the piston.  A steel liner expands differently so needs more clearance.  Once you are sleeved you can't go back since they bore the cylinder larger to accept the thickness of the steel sleeve.  It may be possible to go for a 300 kit or something similar with a larger than stock bore.  KL, keep in mind that although this has been a hassle, look how much you have learned about your bike. Always valuable. Cam.

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