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02 KX250 rebuilding top end

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Hi everyone,

I just pulled the motor out of my 02 KX250 and am starting to do the top end.

Figured I would open up a thread, I will probably have a few questions along the way.

1st Quick Question:

I was wondering if the 2002 KX250 came stock with carbon reeds? I just pulled mine out and found that they are carbon fiber but I thought the stock reeds were white regular fiber? They need to be replaced, I'm thinking either Boyesen Carbon Pro Reeds or Super Stock carbon. Recommendations?

2. I am going to go with a Wiseco Pro-Lite 66.40mm piston/rings and cometic gaskets. Do these gaskets fit good on the '02? I read some things about them not fitting the 05+ KX250's

I can post pictures of the rebuild if anyone is interested.

I'm thinking about painting the frame too.. None of the graphics seem to match the Stock Kawi green anymore and it makes the frame look dirty.. All the graphics I see these days are flo green or neon. I was thinking of either silver like the newer KX's or black (I run white plastics, check out the garage) what do you guys think?

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I used cometic gaskets and a wiseco piston with no problems for the head but the water pump didn't seal well.Top end kit this might not matter,also upgraded to the rad valve with carbon reeds mine came or had a clear like reed but I don't know if it was carbon.All was done with a 265 bore so can't comment on how just the reeds performed.

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I thought all KXs had carbon reeds stock. My 125 and 250s always had them. When they started chipping or warping they were replaced with Boyesons.

The piston for your bike runs from '92 thru 2004. The gaskets may run from '93 to '04 but don't quote me on that one. The '05-'07 engine has a differant power valve setup and piston.

Just type in KX graphics on ebay and see what comes up. Personally I think there is too much dark colors in most of the new graphics. I may be a kawiguy but i'm not into the monster look. I like green and blue, old school, not green and black. Yes the 125 in "my garage" is mostly black but its green and white now.

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I thought all KXs had carbon reeds stock. My 125 and 250s always had them. When they started chipping or warping they were replaced with Boyesons.

The piston for your bike runs from '92 thru 2004. The gaskets may run from '93 to '04 but don't quote me on that one. The '05-'07 engine has a differant power valve setup and piston.

Just type in KX graphics on ebay and see what comes up. Personally I think there is too much dark colors in most of the new graphics. I may be a kawiguy but i'm not into the monster look. I like green and blue, old school, not green and black. Yes the 125 in "my garage" is mostly black but its green and white now.

Thanks, i'm pretty sure everything in the motor is stock on this bike and from what i can tell, it has low hours. I haven't cleaned it up or anything yet, but the cylinder does not show any signs of wear at all. No up/down play in crank. Everything seems to be ok, minus the reeds. I just wanted to replace the top end as it is an older bike and I dont know it's full history.

I'm also not a fan of the monster, not only do I dislike the drink, i'm sick of seeing on every Kawi. I like the blue/green look also. I wouldn't get black plastics, but I think a black frame might look cool with the white plastic.

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Hi everyone,

I just pulled the motor out of my 02 KX250 and am starting to do the top end.

Figured I would open up a thread, I will probably have a few questions along the way.

1st Quick Question:

I was wondering if the 2002 KX250 came stock with carbon reeds? I just pulled mine out and found that they are carbon fiber but I thought the stock reeds were white regular fiber? They need to be replaced, I'm thinking either Boyesen Carbon Pro Reeds or Super Stock carbon. Recommendations?

2. I am going to go with a Wiseco Pro-Lite 66.40mm piston/rings and cometic gaskets. Do these gaskets fit good on the '02? I read some things about them not fitting the 05+ KX250's

I can post pictures of the rebuild if anyone is interested.

I'm thinking about painting the frame too.. None of the graphics seem to match the Stock Kawi green anymore and it makes the frame look dirty.. All the graphics I see these days are flo green or neon. I was thinking of either silver like the newer KX's or black (I run white plastics, check out the garage) what do you guys think?

The stock reeds were CF, not epoxy. I use Boyesen Carbon Pros.

I used to run the Pro Lite, but now I use the Racer's Choice with the TiN rings. If you go with the Racer's Choice you'll have to get the cylinder re-plated, it runs tighter clearances than OEM.

The stock springs will be too soft for moto if you weigh more than about 165 pounds. Especially the forks. I run .44 fork springs and a 5.4 shock spring. The fork springs made a huge difference in keeping the forks from blowing through the travel and making the front whee caster in turns.

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The stock reeds were CF, not epoxy. I use Boyesen Carbon Pros.

I used to run the Pro Lite, but now I use the Racer's Choice with the TiN rings. If you go with the Racer's Choice you'll have to get the cylinder re-plated, it runs tighter clearances than OEM.

The stock springs will be too soft for moto if you weigh more than about 165 pounds. Especially the forks. I run .44 fork springs and a 5.4 shock spring. The fork springs made a huge difference in keeping the forks from blowing through the travel and making the front whee caster in turns.

Thanks for all the info in this thread! I have been enjoying my all original (even the original tires), and low hour "2002" since I got it this spring. Now that I have ridden it enough hours over the summer and fall I am doing some tuning over the winter. One of the things on the agenda is the top end so thanks for this thread. :bonk: The rubber boot between the carburetor and the reed cage has some cracks in it so that gets replaced along with the reeds at the same time. Boyesen's for me.

Another thing on the agenda is new springs so I am glad to see you mention it Chokey. I am 195 lbs without gear and I know I need to go heavier on both springs. All my research has pointed towards a 5.4 (or 5.3, really) rear spring but I was really torn between .44 and .46 fork springs. What made you choose the .44's? The far majority of my riding is on outdoor MX tracks.

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The stock reeds were CF, not epoxy. I use Boyesen Carbon Pros.

I used to run the Pro Lite, but now I use the Racer's Choice with the TiN rings. If you go with the Racer's Choice you'll have to get the cylinder re-plated, it runs tighter clearances than OEM.

The stock springs will be too soft for moto if you weigh more than about 165 pounds. Especially the forks. I run .44 fork springs and a 5.4 shock spring. The fork springs made a huge difference in keeping the forks from blowing through the travel and making the front whee caster in turns.

Thanks for the info. Never heard of the racers choice/TiN rings, where do they sell them? Are they for a different year or something?

I am around 165-170lb, how much do you weigh Chokey?

I'm in South Eastern MA so everywhere I ride is about 0-100Ft above sea level. How do the Carbon Pro's affect jetting if at all? I believe I have all stock jets, and the bike seemed to run great.

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i have had great luck with cometic gaskets and wiseco pro-lite piston/rings on my '99. no leaks, no issues, 2 top ends so far with this setup.

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Thanks for the info. Never heard of the racers choice/TiN rings, where do they sell them? Are they for a different year or something?
Wiseco part # 800M0664 for the '02-'04 KX250.
I am around 165-170lb, how much do you weigh Chokey?
About 180 without gear.
I'm in South Eastern MA so everywhere I ride is about 0-100Ft above sea level. How do the Carbon Pro's affect jetting if at all? I believe I have all stock jets, and the bike seemed to run great.
They made it richer from idle to about half throttle.

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I found those pistons under 800M06640 is this what you have? My cylinder is in good shape, no need to replate so I will go with the Pro-Lite. How does the single ring affect performance?

That is very interesting that it made it richer from 0-1/2 throttle. This is what boyesen recommends for Jetting:

KX250 02

MAIN JET 162

CLIP 2

SLOW JET 55

AIR SCREW 1 1/4

all stock except for a leaner main? weird. i'll have to play around with it if I end up getting them.

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This is the plating worn off correct? What could this be caused from?

check out my cylinder:

IMG_0812.jpg

I can catch my fingernail on the worn part at the top left of this picture:

IMG_0813.jpg

IMG_0814.jpg

worn area is thicker on one side of the cylinder:

IMG_0815.jpg

and the piston:

IMG_0826.jpg

IMG_0827.jpg

I already ordered a new piston/rings... I'm thinking this cylinder should be replated. I dont want to replate and have this happen again. It's weird, its more worn on one side of the cylinder. What do you guys think?

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It needs to be replated. The wear is on the intake side and that is kinda normal if it were on the right or left side I would then think a bent rod as it is I think it is just wore out. The new plating is tougher than the stock plating so I don't think you have anything to worry about on it happening again.

Ed

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needs a replate.. usually poor filter maintenance causes them to wear like that.

good lucky with it...

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thanks guys, i'll be having it replated then.

While I have it apart, i also want to make sure the bottom end is ok. I have read that there should be no up and down play in connecting rod, and there is not, but i do have side to side. From what I read, a little side to side is ok.

Is "side clearance" the side to side play everyone is talking about? Is it measured by it by pushing the rod to one side and stick a feeler gauge in and see what the clearance is or what? Do I need to measure on both sides of the rod? I'm just a little confused, the diagram in the manual just shows a rough sketch of the crank and doesnt give instructions it just says "measure the side clearance with a feeler gauge"

Edited by jkenney177

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I measured the side clearance with a feeler gauge where the yellow on the picture is. is this correct? i came out with .5mm which is in spec.

Untitled.jpg

There were light scratches on the crank where i drew blue scribbles and they went the opposite way that the crank spins?? has anyone seen this before?

Please note: this is not my crank i found the picture somewhere in the forums

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ok heres pics of my actual crank:

measuring side clearance:

IMG_0839.jpg

here are the scratches i was talking about:

IMG_0836.jpg

IMG_0835.jpg

IMG_0832.jpg

Could these be from when they manufactured the crank? maybe they had to shave it down for some reason? i just dont understand how it could happen as the crank spins the opposite way

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No worries with them marks at all. just the manufacturing process where casting flash is removed

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hey guys, i'm removing the KIPS so i can send out my cylinder. is there a trick to pulling the exhaust valves out from the bottom of the cylinder? i have pulled out the phillips head screw on the side that holds the rod in and i have the rod pulled out as far as it will go. the manual just says "remove exhaust valves and guides" so im guessing they just pull out? should i use pliers or something? dont want to ruin anything. thanks

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