KDX250 into KX250 Frame

[jeffcooper]

I've bought a 1995 KX250 bike minus engine, thinking to put the KDX250 1991 engine into it, and adding the lights to enduroize it again - not sure why - just one of those projects we seem to dream up for ourselves! I guess the 95 suspension will be better, although I'd already put some KX forks on beforehand.

The new bike did come with a factory DOMA exhaust as well, so I'm hoping to lose some serious weight if the thing goes together.

I haven't found anything specific in the forum, but any suggestions or comments (apart from the obvious!) would be welcome.

 

[Tom68]

It'll be a better looking lighter bike with a smaller tank, whilst they're worth nothing now, good original ones will be worth something in 5 -10 years. I can't wait so I'm riding mine, it'll be worth nothing.

 

[julien_d]

sounds like fun!

 

[glad2ride]

There was a guy on here about 1.5 years ago who put his KDX250 engine in a L frame (1999 - 2002, I think his was 2000). Engine mounting, cylinder head mounting, swingarm bolt mounting, exhaust pipe routing, etc. are all the areas to check on. Measure twice, cut once, that sort of thing. :)

 

[nearma12]

That will make an awesome bike. I considered doing that with my KDX250 before. I know that the engine should fit right into a 88-89 KX250, maybe a 90-91. The KDX250 engine is externally the same as the 88-89 KX's. I thought about trying to get an older KX and swap the KDX motor. Just imagine a light, nimble KX frame with a torquey 250 2t powerhouse in it. It would be the perfect trail bike. Good luck with the project!

 

[glad2ride]

nearma12, if you are wanting an '88 or '89 KX250, just get the KDX250 transmission gears and swap them in. The KDX250 stock gears are the same part numbers as the '88 - '89 optional wide ratio transmission gears.

(1st, 2nd, 4th, 5th)

 

[nearma12]

nearma12, if you are wanting an '88 or '89 KX250, just get the KDX250 transmission gears and swap them in. The KDX250 stock gears are the same part numbers as the '88 - '89 optional wide ratio transmission gears.

(1st, 2nd, 4th, 5th)

That would work. I would also have to swap the jug, flywheel, and CDI to keep the KDX feel of the motor.

 

[jeffcooper]

Well I'm almost there

I've finally gone for it - and talk about pretty easy! - The KDX engine slips straight in, although the headstay mounts need a bit of filing, or forgetting one of the bolts. The only real work is the swingarm, which you need to chop a bit off the inner sides where they meet the cases, and the bearing bushes to match. You also need to drill out the rear of the cases to match the new swingarm bolt. I was lucky that I got the exhaust, because that fits straight on - radiator hoses can be rejigged to fit as well. For £100 for the 95 bike (essentially a full bike minus the engine) I've got a better looking, slimmer, lighter, and hopefully much better handling bike - I'm thrilled - r at least I will be when I can find the time to rebuild the forks and actually ride it :bang:

 

[julien_d]

Neat :). Good work. No ride report yet, I guess? Look forward to that, and pics!

 

[SS109]

I plan on doing the same swap myself. I'm eager to hear your ride report!

 

[jeffcooper]

Ride(s) report

Well two sides to the first rides - the first was a disaster - first discovered that the rear shock lower adjuster (compression or rebound, didn't matter at the time) span and span, and the new springs in the forks seemed to be a bit strong. Also, the swingarm chain length adjuster broke off the nut end, so although I tightened the axle as hard as I could, the trip was cut short by the wheel suddenly flicking to the right!! Even so, the difference in feeling due to the lighter frame was incredible - it felt like a new much more powerful engine, not a new frame.

Back to the workshop, where the shock problem was discovered to be worse - the clevis thinner side (the one with the adjuster!) was cracked because someone (me!) hadn't checked the lower bearing fit, and tightening had bent it inwards. Rebuilt the shock, and took a chance on making sure the lower fit was better second time round. Seemed to work, so blew the air up to a proper 150psi, set everything to just off soft (or at least the ones that worked) - bodged up a new chain adjuster - ran the lock nut all the way in to the swingarm, and then used a bit of tube which then pushed backwards upto the axle block.

Second ride - wow! didn't go far because of time, and did use some of that time playing with suspension settings - but even though I now needed a front brake which isn't up to braking duties at the moment - the ride is just a different world. The wheel comes up in the lower gears, which is a bit of a novelty, and very useful, and I will have to become a much better rider to cope with the speed that now comes naturally.

Whatever the potential problems, this was a fantastic rebuild, and I can heartily recommend it - anyone want to buy a very good condition original KDX frame?

 

[jeffcooper]

Further report

Well I've been enjoying my new KX framed KDX 250, up until yesterday, when I paid big style for not fitting the petrol tap with a reserve feature into the KX tank !!

After pushing/freewheeling approx three miles (which for an old git like me is a lot) I didn't know wether to hate the thing for leading me off into some woods at the bottom of a hill, or thank it for weighing a lot less! Surprising how different a trail that you ride every week looks at walking speed - uphills appear that you didn't even realise you were riding when on the bike!

Anyway, today's first job was to fit that reserve feature - very easy, just an additional hole in the KX tank - although I did shorten the long pipe to reduce the amount of reserve gas, and so I don't have to put so much in in the first place - and the second job was to go rescue my t-shirt which fell off me half way back on the long push yesterday.

Still love it though - best thing I ever did! :cool: