Modify frame instead of engine cases ?? KX250 to KDX250

[snopro753]

The traditional method of building a KDX hybrid is to drill the rear cases mount out to 17mm to fit the KX250/KX125 17mm OD swingarm bolth and frame passages. I have a 1993 KDX 250 that I was considering building a hybrid out of. It also has a 15mm swingarm bolt diameter like the KDX 200. So it needs to be drilled out to fit KX250 frame as well.

But I got to thinking, if I wanted to use the KDX 250 swingarm I could just buy a 15mm ID x 17mm OD bushing like the one pictured below. Press it into the KX250 frame, use the KDX swingarm bolt, bushings, and swingarm on the KX250 frame. I need to verify the distance between the frame is the same between the KX250 and KDX250 frame along the axis of the swingarm bolt for this to work. But if it did it would allow the use of the KDX250 rear wheel, spacers, and axle I already have.

Just an idea I had this morning as I was headed to work.

Any thoughts or things I haven't considered?

[Tedh98]

But I got to thinking, if I wanted to use the KDX 250 swingarm I could just buy a 15mm ID x 17mm OD bushing like the one pictured below. Press it into the KX250 frame, use the KDX swingarm bolt, bushings, and swingarm on the KX250 frame. I need to verify the distance between the frame is the same between the KX250 and KDX250 frame along the axis of the swingarm bolt for this to work. But if it did it would allow the use of the KDX250 rear wheel, spacers, and axle I already have.

Just an idea I had this morning as I was headed to work.

Any thoughts or things I haven't considered?

That is an interesting idea.

I would assume that the KDX linkage and mounting location is different than the KX suspension. I'm not smart enough to figure out what different lengths or angles of the rear suspension components will have on the function of the rear suspension. So if you could get the KDX swingarm and linkage to bolt up to the KX frame, the functionality or ride may be unacceptable.

OR . . . you could end up with the best rear suspension ever made.

[snopro753]

That is an interesting idea.

I would assume that the KDX linkage and mounting location is different than the KX suspension. I'm not smart enough to figure out what different lengths or angles of the rear suspension components will have on the function of the rear suspension. So if you could get the KDX swingarm and linkage to bolt up to the KX frame, the functionality or ride may be unacceptable.

OR . . . you could end up with the best rear suspension ever made.

I will probably end up the former. I am considering buying a 2003 KX 250 frame just to weight it and see if I end up with any real weight loss vs KDX 250 frame. If there is enough to justify the hybrid then I could proceed with this idea.

Additionally I was looking at the KX 250 frame and the thickness of the area the holds the swingarm bolt is very thin. The bushing above would be way too long and need trimmed by a large amount. I am afraid it would be so thin it would become damaged rather quickly.

I need to investigate this more but it seems to me there is a reason no one else has completed this yet.

[Tedh98]

I need to investigate this more but it seems to me there is a reason no one else has completed this yet.

Maybe not with the newest frames, but there are at least two 250 conversions just in this thread: http://www.kdxrider.net/forums/viewtopi ... id#p152920

I think there have been some others.

[argclh6670]

We bought a 92kdx250 that came with a 96 kx250 roller.....it took me about a year ofcthinking about it to finally do the swap....the 92 engine slipped in with very little hassle except for having widen swingarm to accept to kdx motor. It was a cinch....the bike now is a good 20+ pounds lighter and handles so so much better! Id say proceed!!

[Tyl3r]

Additionally I was looking at the KX 250 frame and the thickness of the area the holds the swingarm bolt is very thin. The bushing above would be way too long and need trimmed by a large amount. I am afraid it would be so thin it would become damaged rather quickly.

I was thinking about this and I think I could potentially see it working. If the bushing thickness was exactly the same as the frame thickness where the swingarm pivot bolt hole is, the bushing would essentially just be another bearing spacer in the stack there. When you tighten down the pivot bolt, the bolt heads would bottom out on the frame, and clamp the bushing in place along with the bearing spacers/bushings. Right?

I'm not 100% familiar with the KX250 frames, but I know on my 125, there is a "bulge" in the frame that makes a flat to prevent the pivot bolt from spinning. I don't think this would work on the 125 due to that bulge. I think part of it would end up getting drilled out. If it did, then it may not keep the pivot bolt from spinning when tightening the nut down.

[KDXGarage]

"buying a 2003 KX 250 frame just to weight it and see if I end up with any real weight loss vs KDX 250 frame"

Sadly, the KDX250 frame is MUCH heavier than the 2003 KX250 frame and subframe combo. It is noticeably heavier than the 1989 - 1994 KDX200 frame and sub-pipe combo, even if you don't have the two rear hand hold pieces bolted on.

[snopro753]

"buying a 2003 KX 250 frame just to weight it and see if I end up with any real weight loss vs KDX 250 frame"

Sadly, the KDX250 frame is MUCH heavier than the 2003 KX250 frame and subframe combo. It is noticeably heavier than the 1989 - 1994 KDX200 frame and sub-pipe combo, even if you don't have the two rear hand hold pieces bolted on.

Thank you for the reply. I believe you. I would like to weigh it and see how much it actually is. I plan to soon, just need to make a point to do it.

[KDXGarage]

I think I did it and posted the info back in '05?? I shall search...

SON!! I still have a damn fine memory.

http://www.kdxrider.net/forums/viewtopi ... 100&t=1462

A Few KDX Frame Weights
Postby Jason » 10:49 pm Oct 08 2005

Here are a few KDX frame weights that I weighed. These weights are for the frame and two steering races.

1987 KDX200 - 22 pounds (no paint)

1991 KDX250 - 28.5 pounds

1994 KDX200 - 23 pounds