2003 KX 250 SF Conversion

[umberto]

zz3gmc gave a lot of great info on doing this swap. You do need to trim the swing arm and bearing sleeves, but thankfully the motor mounts line up at the bottom and with the swing arm pivot, so you just measure and trim. Another great tip he gave me was to use a 2005 or later tank. The heads on the later models sat more upright, requiring a more shallow tank. This helps a lot with the obviously taller K5. Thank you zz3gmc!!

[umberto]

Good deal! That's a nice looking '03.

I can't speak for the Magura hydraulic conversion on a KX500, but I do have one on my '00 KX125. With all the clutch abusing required to ride a 125, I think it's a pretty good barometer for the Magura system.

I've had zero troubles with the slave cylinder, but I've had to replace the seals a few times on the master cylinder. As for performance, it's everything it's supposed to be: self-adjusting, easier lever pull.

Motocross Action featured a KTM/KX500 that used a Magura hydraulic conversion. The 250SX uses a Magura master cylinder, so they just added the KX500-spec Magura slave cylinder. I assume it worked well.

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Thank you!  It was a long drive to get it, but I think it was worth it.  The motor is very nice, and the bike is in great shape.  I'm going to be selling the motor so it was the most important part to me, but the rest of the bike should clean up well. 

I have had a weird issue with my slave cylinder. It was making a weird sucking noise when I got home.  I assumed it had a blown seal and it would quit working at any time. After a bit it stopped and the clutch still works very well. It was raining pretty heavily when I went to get it, so maybe it was water that was being forced out from around the seal. Has anything like that ever happened to yours?

[zz3gmc]

You can use the stock 03/04 tank. If a big tank is needed then use the 05-07 KX250 Clarke/IMS tank.

[umberto]

Gotcha.  Do you need to heat and bend the stock 2003 tank to get it to fit?

[KevinTwoStk]

My Magura slave cylinder makes the same noises you're describing after I wash the bike or anytime the slave cylinder gets wet. I wondered about it, too.

I've always used Magura Blood mineral oil in my clutch system. I've heard you can use common mineral oil from the drugstore but have never tried it--likely never will.

[umberto]

My Magura slave cylinder makes the same noises you're describing after I wash the bike or anytime the slave cylinder gets wet. I wondered about it, too.

I've always used Magura Blood mineral oil in my clutch system. I've heard you can use common mineral oil from the drugstore but have never tried it--likely never will.

That's a relief, that sound was freaking me out.  I've always used Magura Blood as well. I'm like you, why take the chance?

[umberto]

I made some progress on the bike today.  I built a platform to hold the engine level and leveled the drill press as well.  The hole drilled cleanly and quickly.  Whew!



While I was doing the drilling, my 15 year old son stripped the bike down to pretty much nothing.  It makes you proud to see your son using the things you've taught him. Here's a picture right before he pulled the swing arm.



After some fiddling, I was able to get the motor in the frame. I went ahead and cut off the front motor mounts and trimmed back the head stay so they would be ready to weld. I just need to trim the swing arm bushings and install them back in the already trimmed swing arm to have her rolling and ready to pester my welding class instructor for advice.  

[zz3gmc]

Looks like the 88 engine has more room for radiator clearance due to the lack of the 3rd powervalve that the 89 up engine has. I cut the lower rad mount off of my frame and moved it about a 1/8th" forward so the radiator tank doesnt touch the head. I removed the clutch cover and basket so the engine had a flat surface to rest on. I had my machinist buddy open up the pivot hole. The next one I build I'll do it myself. Lookin good!
 P.S. If you decide to get rid of the 03 forks let me know! When properly revalved they are the best forks Ive ever had for offroad! I swapped a set onto my 07 250, 04 500 hybrid and my wifes 04 300 big bore. With a set off Flexx Bars and 03 forks it will eat up rocks, roots and all sorts of trail junk!

[umberto]

I was so nervous drilling that hole out that I leveled everything in site, including myself.  I used the all thread and the nuts to allow me to adjust the motor up and down to level everything.  It was a lot easier than I thought, you're really just drilling a little bit on both sides not the entire hole.  The motor went in the frame really easily too, once I took off the two 90 degree elbows for the cooling system.  Lord knows I took it in and out enough times yesterday as I fiddled with stuff.  I'm pretty excited to get it back into a roller so I can start fitting the exhaust.  I know I have a ways to go before I'm done, but it was nice to get the first steps out of the way.  I'll be ordering some goodies this weekend to start redoing some of the hard parts.

I'm thinking about sending the suspension to Race Tech.  The forks are leaking, and the shock is in major need of a rebuild.  I had my 07 suspension done by Factory Connection and it really turned out well (it ended up on my 04), but I wanted to try a Race Tech re-valve with the gold valves.  Does anyone have thoughts on which one is better?

[umberto]

Made some more progress today.  I was able to get the swingarm and swingarm bushings trimmed down and installed.  I left everything a little big and then slowly fine tuned it using my belt sander.  The swingarm moves really easily, and the chain is in perfect line.  I am going to replace all the bearings, and the rear end should be good to go.  I'm pretty excited to have it this far.  On to the exhaust and motor mounts!

[sandblaster]

I'm thinking about sending the suspension to Race Tech.  The forks are leaking, and the shock is in major need of a rebuild.  I had my 07 suspension done by Factory Connection and it really turned out well (it ended up on my 04), but I wanted to try a Race Tech re-valve with the gold valves.  Does anyone have thoughts on which one is better?

I've rode both and if set up correctly for you and your riding style it would be difficult to tell them apart.
I use Race Tech because the set up options are more varied and they make it easy to get a good starting point.
Whichever you decide on, spend a few extra dollars and use the low or zero drag oil.
I love the difference it made on my K5.

[umberto]

Did you do the gold valves or did you just have them re-valve your suspension?  I've heard really good things about the gold valves, so I thought I would give them a try.  I'll definitely request the low drag oil.  Thank you for the advice Sandblaster.

[sandblaster]

Did you do the gold valves or did you just have them re-valve your suspension?  I've heard really good things about the gold valves, so I thought I would give them a try.  I'll definitely request the low drag oil.  Thank you for the advice Sandblaster.

I did my own suspension and used the gold valves.

[umberto]

I got to do a little more work on the conversion today.  I was able to fit the CR 500 pipe.  It actually does fit really well, except the neck had a bit of a curve in it.  When I cut off the flange, it left a funny angle.  I somehow managed to match that angle in the neck from the KX 500 I cut off.  It's a classic example of a blind squirrel finding a nut eventually.    I'm going to take it to a welder and get him to weld the neck on, and then I'll work on the mount and "relief" for the coolant hose that runs to the head.  More pics to come.

[umberto]

I got my pipe back from the welder in record time. After a few tweaks, I was able to get it to fit.  I still need to do the bottom mount, and then it's off to the pipe repair shop to get out those really bad dings.