Posts
174
Joined
10/17/2013
Location
Crystal Lake, IL
US
Edited Date/Time
5/11/2018 9:50am
Bike Builds has always been my favorite forum on Vital. So, when a friend called on Xmas eve and said that he had a KX 250 for me I figured here's my opportunity. It won't be anything too fancy. Just a solid rebuild and a few items to bring it up to current performance standards.
Here it is as received.
Clutch cover has a dent that turned out to be a crack.
Radiators are straight which is surprising for original pieces.
Air filter has been maintained.
Wheels are straight.
But, the left lower fork leg has a dent.
Here it is as received.
Clutch cover has a dent that turned out to be a crack.
Radiators are straight which is surprising for original pieces.
Air filter has been maintained.
Wheels are straight.
But, the left lower fork leg has a dent.
Motor will be gone through with a full rebuild.
Not looking forward to stripping the swingarm.
Here's the motor blasted and ready to be sent out for vapor blasting.
And here it is back from vapor blasting. The Hot Rods crank that was in it was ditched for an OEM crank and a ProX rod. The rest of the components are ProX or OEM including all new trans bearings.
Here it is with a fresh cylinder from Millenium, all new seals, bearings, a complete clutch assembly, and, new OEM bolts. We also did a little head work and added some epoxy in a couple areas in the cylinder.
Swingarm and linkage ready for new bearings.
But, not until it's machined for a 25 mm axle.
I picked up a set of Showa 47 mm forks and triple clamps from a 2009 KX250F. The Showas have a 33 mm lug offset and that year triple clamp is 23.5 mm offset. The combination will have the net effect of going from a 22 mm clamp to a 21.5 mm clamp on the stock 99 forks. I had to weld a new steering stop on the frame to use the 09 triples. Those footpegs are 2014 KTM and are a direct bolt on. That will give me a lot more options for pegs. The triple clamp has the casting marks removed and I Cerakoted it burnt bronze.
Shock received a new seal head, piston band, and bumpstop. The clickers are in perfect shape. They don’t look like they've ever been adjusted. Spring is a 5.0 kg/mm from Factory Connection.
Not a fan of the logos on the covers... so they're gone. They turned out well using a 4" wide belt sander w/36 grit followed by an orbital sander with progressively finer grit in 3 steps. i'll blast these and finish with Cerakote.
Since current KXF rear wheels use a 240 mm rotor (99 was 220 mm), I'll be running a 2017 rear brake. But first I'll have to address the issue of the caliper alignment bracket on the swingarm.
And here's the bracket having been addressed.
With the bracket out of the way I can mock up the 17 caliper. The caliper will have to be rotated 10 degrees counter-clockwise around the axle to clear the swingarm. That will mean machining a caliper bracket as well as a new bracket for the swingarm.
The new swingarm bracket was the easy part. It's held in place with a screw for mock up. Once fitment is verified I'll TiG weld it in place.
For the caliper bracket I machined off the area with the slot for the swingarm bracket. Then I TiG welded a piece of aluminum in its place and machined a new slot to provide the 10 degrees of rotation. I Cerakoted the caliper and bracket burnt bronze along with the engine covers.
Here it is finished
The front is a 2017 Nissin caliper that's been rebuilt. For the master I'm going to try the rebuilt 99 as it is a 9.5 mm piston. The goal is to achieve the same feel as my KTM Brembo. The 99 master is updated to the 2018 push rod so I can use a current style lever. The rotor is a 270 mm OS from Galfer.
So I sourced a new take-off shock and proceeded to machine the body to shorten it and machine a new circlip groove for the seal head. I also had to machine the clevis and rebound rod to get the required OAL. Race Tech supplied a 20 mm shorter spring. Valving was light on the low speed a firm on the high speed for this year. The high speed uses .30 mm shims in 1 mm increments, so I removed every other shim to have 2 mm increments as a starting point on the 250. I also had to machine a small amount of clearance on the reservoir to clear the frame. The subframe was also modified as was the body above the compression adjuster.
Up front I decided to go with a set of KYBs. These are new take-offs from a 2017 YZ250F. I'm going to start with stock valving, but changed the springs to 4.5 N/m. For triple clamps I used a set from a 2007 KX450F. These have a 24.5 mm offset to work with the KYB lug offset. The forks also required a new caliper bracket, hub, and rotor as the axle is 22 mm and the KXF axle is 20 mm. Faster USA made a YZF hub and anodized it green. Unfortunately, the green is very dark. I ended up machining the KXF hub to use the FasterUSA bearings. Their bearing has a smaller OD than a stock YZF bearing.
The Shop
I had KX's all though the 90's, the last 2-stroke I owned was a 99 with Ohlins forks... my favorite.
I decided to try the footpegs from Next Components. I machined a set of titanium pins.
A KX build has to have a R304 Shorty and a PC Works pipe... my opinion of course. The R304 Shorty is readily available, not so for the pipe.
I finally located a new pipe that had been laying around since 1999.
The first thing I did when I got the bike was to go on Babbit's and order every oem bolt on the bike. This took almost all day to look up every bolt. As you can see in this picture, I missed the bolt for the radiator bracket. What you can't see is that I also missed the 2 for the power valve cover, 2 for the subframe, and 1 that holds a pin for the power valve arm. I remembered when I placed the next order.
2007 front plastic. Bars are Carmichael bend.
WC clutch perch and ODI lock on grips- soft.
Carb was rebuilt and uses Pro Circuit jetting , new carb manifold, and Boyesen Carbon Pro reeds..
Brake pedal was modified for a Hammerhead tip. The pivot hole was reconditioned by machining it for a press-in bronze bushing. The pivot bolt is for a 2017 and has a larger diameter thread. The frame was drilled and tapped for the larger thread.
I'll update with photos when I get graphics...
I'll ride with a second set of plastics with my number.
The vapor blasting was done here: http://www.arnoldsdesign.com/Vapor-Blasting.html
I'll have to wait until June for a comparison to a '19 250SX. For now I'll have to compare it to a 350SXF... also with KYB cartridges. Even though the KX wasn't the best turning 250, I still think it will be better than any 450. Suspension-wise I hope it's as good as any modern bike... we'll see soon.
Great bike build.
On my ‘00, to get a 240 rear rotor, 25mm axle i just bolted a 03 up swingarm on.
Nice bike.
Pit Row
It’s a fairly simple procedure for someone with a vertical CNC. The link I provided above for vapor blasting also list machining as a service...
The '03 swingarm was an option I considered and I actually sourced a swingarm early on. But, since the '03 swingarm is very different visually from the '99-02 swingarm, I chose to stay with the '99. Also, a certain amount of satisfaction was derived from adapting modern wheels/brakes to the '99 swingarm... not so much when I bolted on the '03 swingarm.
Cool bike. Something about that era. Im into 500s, id still like to convert a 99-02 250 into one. Always thought thatd be a good home for a big kx.
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