90 KX125 Compression!

[VooDooChile]

There are a few things I've been wondering. I'm in the middle of rebuilding a 1990 KX125 I bought not too long ago, and finding all sorts of stuff out as I go along. Right now, I'm contemplating a top end rebuild. I just checked the compression on the motor, and it was sitting at about 135 psi. Is this enough, and if not, what should the ideal amount of compression be for this motor? If it were say, 160 or so, how big of difference would I notice by rebuilding the top end?

Also, I heard on these cylinders, it's a good idea to have them sleeved and bored. Bumping up the displacement. I've heard it's a fairly common thing to do, and was curious about looking into this.

I JUST got done putting on my new Chain, Rear and front sprockets, (Thanks Sage!!), and I want get the rest of this done while i've got the bike torn down. I want to get back to riding!!

 

[cr25096er]

135 is pretty low. a new top end should get u about 180-190psi.

 

[VooDooChile]

Would the addititional 60 PSI be a noticeable difference? I guess I'm just trying to figure out if it's time to rebuild this motor or not.

 

[imlostagain]

Sounds like you are definately due for a top-end.Cosidering the age of the bike and not knowing the history I would atleast disassemble the topend and check the condition of the parts. A top-end is a lot cheaper to do now than if the piston shatters due to not being within spec. As for any cylinder work look into Eric gorr's site . He has a WEALTH of info and did an excellent job overboring and replating my cylinder.

 

[cr25096er]

i dont know how much of a performence difference u will feel but i know u will feel a difference if the piston shaters and u have to hang onto the bike s u dont go flying forwerd

 

[125 rider]

You'll notice a power increase especialy down low. I wouldnt put a sleeve in that bike as it changes heat transfer characteristics and will wear faster.