500 KX500 PF

The PF is for perimeter frame.

I finally got to the point where I could start this project.

The chassis is a '92 KX250 which was my primary ride for over a dozen years. I scored an '08 KLX450 front end and shock for it on Ebay. The engine donor bike was an '87 KX500, but I have since gotten enough stuff to make the engine an '89 to '04.

This bike will be used for trails.

Enough with the background. I started the basic engine mounting a few weeks ago. I bored for the swingarm bolt as a starting point to get a baseline. Obviously, the front mounts were not even close:



Before and after them being cut off:





The mockup before welding:



After the welding:









The lower mount was so close to where it needed to be that I decided that it was a waste of time to try to move it like I did the front mount. I could have left it alone and used an 8mm bolt, or shave it a bit oval (.020") to use a 10mm bolt. I went with the ten.

torch
 
Now you see it:



Now you don't:



How I got there:





The above work was the roughing in part, and I got to the after part with a die grinder. I sand blasted the area to try to make it look like the as-cast surface of the rest of the head. My goal was to make it look like the factory cast it that way (without the rear headstay):

Playground sand worked good!



torch
 
The tank still needs to go down about 1/2 to 3/4 inch, and it is sitting on the head right now. It was much worse with the headstay there. I might still need a shorty plug, too.



I got the tank done. At least I hope so, since I don't know what else will get in the way.

I used a heat gun to get it to about 250 degrees, then used my drill press as an arbor press with a bungee cord to hold it. The thing between the drill press and the tank is the ball from a 2 1/2 inch valve.



This is the clearance I got:



It's not the 1/2 inch I wanted, but it looks good to me.

torch
 
Awesome build and great job so far. The removal of the head mount looks great!

Have you looked into what it's going to take to mount the KLX front end on this bike yet?
 
Awesome build and great job so far. The removal of the head mount looks great!

Have you looked into what it's going to take to mount the KLX front end on this bike yet?
All I need to do is fab and weld on some steering stops to the frame. The head bearings are the same, and the headtube length is only different by 1/16", well within the adjusment range of the triples.

The shock will require a bit more for mods, but it is doable.

torch
 
Isn't it going to vibrate pretty bad without the head mount to triangulate the motor?
It will have a head mount, it just won't be to the rear.

The KX250 frame uses a front headstay. A rear headstay is out of the question for this frame, unless I want to make a custom 1 gallon tank.

I thought of welding on a front mount lug to the head, but I found a better option. There is a man over at KXriders.com (where I have gotten many ideas and help) that makes a stainless bolt on front headstay. He is jfabmotorsports. I can do almost anything that I set my mind to, but I have learned that there are people that are more efficient than I am, and I need to save my time and buy thier stuff.

If anyone else has questions about this build, feel free to ask. I posted all of this to give everyone an idea of how to do this conversion, and also to get some ideas out there for anyone else that is considering a hybrid bike.

torch
 
It will have a head mount, it just won't be to the rear.

The KX250 frame uses a front headstay. A rear headstay is out of the question for this frame, unless I want to make a custom 1 gallon tank.

I thought of welding on a front mount lug to the head, but I found a better option. There is a man over at KXriders.com (where I have gotten many ideas and help) that makes a stainless bolt on front headstay. He is jfabmotorsports. I can do almost anything that I set my mind to, but I have learned that there are people that are more efficient than I am, and I need to save my time and buy thier stuff.

If anyone else has questions about this build, feel free to ask. I posted all of this to give everyone an idea of how to do this conversion, and also to get some ideas out there for anyone else that is considering a hybrid bike.

torch
Nice work, very professional and well thought out.:thumb: I'm like you, I can fab just about anything but sometimes it's just better to bite the bullet and buy something because you're time has a value to it.
 
I tore down the 250 today to explore the shock fit, and there are a few issues. The 450 shock is 7/8" longer than the 250shock.



As you can see, the yoke on the bottom of the 450 shock is much longer. I think there is enough room to move the hole, though. Before I do that, I need to do further research on the linkage ratios of both bikes. I want to make it fit AND work like it does on the KLX450.

Other issues to be solved.... The subframe and seat do not clear the adjuster area of the shock, but the plastic does:







Modifying the sub and seat won't be too bad, but I did gain a lot of clearance in one area: under the shock reservoir where the pipe goes under. That is one spot where extra room is greatly needed.

250 shock:



450shock:



torch
 
Problems solved!

I made an angled cut out with the holesaw to clear the clicker:



I made a solid insert to fill the hole and welded it up. Also I drilled and milled the yoke where I needed it:



Here is how it clears now:



Next up is to make frame stops for the triples.

torch
 
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