KX250F/KX500 convertion

[TerryK]

We are looking at building a couple of AF 500s for ice racing and need some advice from the guys that know their s**t (you!). I've heard good things about JFab frame rails. Do they also sell the engine mounts to go with the frame rails? We want to use 2006 KX250F chassis if possible. Any advice would be much appreciated.

Thanks in advance!

[cbrfrenzie]

We are looking at building a couple of AF 500s for ice racing and need some advice from the guys that know their s**t (you!). I've heard good things about JFab frame rails. Do they also sell the engine mounts to go with the frame rails? We want to use 2006 KX250F chassis if possible. Any advice would be much appreciated.

Thanks in advance!

Typically in any of the conversions you would fab the mounts your self, as any slight change in engine mounting position, intake boot choice, etc. will change the position and shape of the mounts.  Everything I have read and seen have been hand made mounts after the engine was positioned in the frame during mockup.

Whats going on with that front brace thing??

[scooterVOOII]

The brace would be to keep that metal stud laced front wheel from tearing the hide off a comptetitor in a corner, or anywhere, for that matter.  (Think treechipper)  Plus if you take a tumble, well.......
Some have them on the back wheel as well.  Imagine doing 60 mph and having that thing sawing on your ass.   Welcome to ice racing and cold northern climates.  In Canada, we have 2 seasons.  Summer, and 4 months of riding at -30 celsius.

[brooksie]

I'm in Canada too!

A project like this needs to go to somebody who really knows what they are doing regarding fab work. Either previous examples of their work, or reliable recommendations are what you need. This is a MUST!
Once you've found your guy, making the frame rails will be a piece of cake for him. Positioning of the engine is critical to get "some" clearance where needed. Even then, things are tight in the 250 frame and a bit of fiddling here and there will most likely be required. In reality, there's not much space to work with anyway.

Having the SH pipe on hand will be a big help with setting up. If you haven't got one already, get it on order as sometimes they take a while for a batch to come through if they are out of stock.

As mentioned, the mounts are made after the frame rails have been welded into position and the engine rigged in its final position. I would suggest making the front mounts removable as the engine is a SOB to get in and out. Plus, it really does make the finished article look very "right!" I'm no fan of the front mounts being welded to the frame. I know the SH bikes are like this, but it looks really gash to my eye. Hopefully, I'll be able to upload some pics of mine in a week or so. I was very pleased with how things have worked out on my build the last time I went to see it.

Then there's the air boot and radiators. Still trying to get some straight answers regarding these. I'm kinda leaning towards ordering a set of standard KX500 rads now, after changing my mind several times. If you could give me the dimensions off your bike, that would be a help!
The original 250F rads, well the right one can be reused but the left is way too long. Hope this helps.

Cheers

[cmotodad]

Brooksie,


I would look into CR125 radiators or CRF250. On my CRF250/K5 build the radiators are not taking alot of rework. Have done a CR5 in a 125 frame and they worked good too. Couple mount changes might do the trick.

[don46]

I would go with the Jfab rails, service honda cuts the stock set and mounts a piece to fill the gap, I don't like it. I've done 3 now and did the first like that, the second was a 250 2s and the last a 500, on the last two I bent my own rails (used a JD3 bender for square tubing) using the radiused tubing and they came out great, looked just like the Jfab rails. you really don't have much in the way of options when installing the motor, it really does have to be positioned properly, the center line of the countershaft has to be in the center line of the swing arm, if you roll the motor up the chain get loose as the suspension compress and of course as it goes the other way it gets tighter, so like the stock you have to have a compromise, and fudging one way or the other can have consequences. So don't position the motor for reasons of clearance or anything else, the clearance is what it is and you have to live with it, having said that I think my 500 has more clearance that the 450 did.

The other thing, I think Sandblaster is on to something with the duel headstays, I haven't done it yet but may.

I used a 250f for the 250 2s conversion but not the 500 conversion, for some reason, and I may be wrong, I thought there were issues with the tank hitting the motor, but don't hold me to that, was it sandblaster that said he melted a hole in his tank trying to form it or somebody else. The 250f Showa suspension bolts right up to the 450, thats what I used on my latest.

Worth the effort for sure, by the way, I also like (maybe even more) 04-05 250f steel chassis, good suspension (newer will also bolt right up) and they feel narrower than the Aluminum chassi bikes

Good luck

[alexander-vmann]

i think you should go with a newer frame. or a steel frame. 06 was the first aluminum frame (along with the kx450f) attempt by kawasaki. so you would be better of with 08. it is basicly the same frame but with improvments!