the 250/500 project

[supermotokx]

Hi All

This is it!   The first pictures of my '98 kx 250 with the '96 500 engine in it check out the gallery. I know I'm late but I've been very busy the last weeks. The pics are kinda crap, but I'll have a lot more to come with more closeups, the finished pipework, brakes, cooling system etc. Stay tuned.

Martin  

[John]

Congratulations!

That's a mean looking bike you have now!

Have you noticed any change in the way it handles? (Obviously you have   ) I mean any positive and unexpected news?

/John

[supermotokx]

Well there are plenty of changes:

1) The frame fells alot stiffer and so does the swing arm which means it steers better going out of turns on the throttle. The stiffer frame probably allso accounts for the better steering going into turns, but that may be the 250 forks as well (way better for supermoto than the 500 forks).
 One of the first things you notice is how you sit on the bike. You're able to get much more weight on the front because of the tank and seat of the 250. That really helps going into turns.
 Because I had to modify my FMF pipe, I've lost a little top end power but feels like I've gained more low end. But it's not really a problem, i still haven't done anything else (like v force, big bore ect) to the engine so I think we can get that power band back. I did look for a complete made-to-fit pipe and found that Jolly Moto (Italian company) and Van Hasselt (Belgian company) makes race exhausts for the 250/500 combination, price: 5-600 $. That was not really within my budget.

Martin

[John]

Nice!

Now that you mentioned it, how much have you spent on the conversion? I have a KX125 and a KX500 motard. I am planning to do the same thing, depending on the amount of spare time (= none).

I think I read somewhere that you had to cut in the 250 frame to fit the engine? Is there something else apart from the expansion chamber that caused you problems? Can you change the sparkplug and jets easily?

Sorry, loads of questions... Maybe you should write a Haynes manual   . I'll definitely buy it!

/John

[supermotokx]

Well here's my haynes manual:

1) 250 Swingarm (alot stiffer than the 500) is too wide for the engine
Solution:
-Grind approx. 2 mm of each side.
-Do the same on the 500 engine mounting bracket (quite difficult to do as it has to be precisely alligned with the swingarm bearings)
-Cut the swing arm bearings down to size.

2) The 500 engine has a 15 mm bolt hole. The 250 swing arm has 17mm  
Solution:
- Drill the engine hole to 17 mm.

3) Engine is big compared to the 250, even when lowered as much as the mounting brackets lets you do (actually the brackets are not the problem, but you have to get the bolts through as well...). This means no room for the tank.
Solution:
- Cut off the top engine bracket and throw it away.
- Modify the tank with plastic padding to fit the sparkplug (use chemical metal - no big problem) or raise the front of the tank apx. 10 mm.

4) Exhaustpipe doesn't fit the 250 frame.
Solution:
- By a new exhaust (600 $)  
- Cut up the old one, turn it and bend the last part (where it's not expanding). Get some weld-god to weld it back together.

5) 250 engine fittings doesn't fit the 500 engine.
Solution:
- Cut off the 250 fittings.
- Weld on new ones to fit the 500 engine (piece of cake   . You will not have to cut in the frame at any time).

And you're done  

Parts used from kx 500 :
- Engine
- Ignition
- Cooling system (you could use the 250 I guess - I just didn't have it)
- Karb (but not airfilter and airbox)

Parts used from kx 250 :
- Everything else

Upsides:
- Handling      
- Looks    
- Coolness        

Downsides
- Changed powerband (from the exhaust fiddling)    
- Tank must come off to change sparkplug  
- Work hours      

Cost:

Hours in the garage: 75 (most was thinking about: How the hell am I'm going to do that??)
$ paid: 75 for the exhaust rebuild.

You will need to have a well sorted toolbox the fix all the precise drilling and grinding.

I would think that thework needed to be done is the same for a 125 frame. But you need to check if the frame is too small for the big 500 engine.

Let me know if you have any more questions. And I'm sorry about my crap English, but I'm from Europe so I can't help it.

Martin

[John]

Thanks,

I might take you up on the offer and come back to you with one or two questions.

By the way, don't worry about your English. I am also a "stupid foreigner" i.e. non-English. You have to see the benefits - how many English speaking persons are bilingual?

/John - the Swede (as in Swedish - not the vegetable)

[K5RACER]

Ok step 5. what fittings dont fit? can we get a closer pic of exactly where and what you had to cut and weld?

[supermotokx]

I'll upload all the closeups in a week or so. I've got pics of all my mods, so hang tight.

Martin

[kxtaz]

i would be willing to weld pipe together for you.im fairly experience welder i own a  mig welder and  tig welder.ive posted some pics of  my welding in forum a while back.i welded some stuff for a couple different pitbull members.i will even do it for free.From my experience with welding dirtbike pipes in the past  its much easier and you will get a much cleaner looking weld if you modify brand new pipe.riding bike causes exhaust pipe metal to become  brittle [this is especially true with stainless,chrome or nickel finished pipes]this is caused the heating and cooling process.another problem is carbon buildup inside used pipe.during weld  the carbon in pipe is ignited and causing hot spot in sheetmetal making it very easy to burn through material  harder to run long consistent beads with carbon buildup  inside pipe. materials tempature will be very inconsistent the heavy carbon areas will burn thru easy. you can use lower setting  to prevent burning through then you dont  get good penetration in area where there is no carbon buildup.Repairing  a dent or sm. holes in a  used exhaust pipe is pretty simple and simple wirefeed welder will usually work fine.its a little trickier to weld factory looking seams throughout a complete pipe.if you are interested in me fabricating or  modifying pipe  for your bike.let me know.You would definitely need to have pipe already cut,pieces formed,fitted and well marked as to how they are supposed to go together.best way to mark is by careful fitting pieces together when you have good fit,proper bends  and everthing aligned properly.use a crayon and scribe lines across areas or seams where parts join together.crayon marks can then be used as alignment points when fabricating. if you use a couple different colors its even easier

[kxtaz]

i looked at pics of your pipe.i think your better off using kx250 pipe with kx500 exhaust port flange.since you are using kx250 radiators,shrouds ,sidepanels and really didnt do any modifications to the 250 frame.a 250 pipe should still fit pretty good from radiator all the way back to rear fender.you would just need fabicate about a 8 in. section from exhaust port  to somewhere just below radiator or wherever you  choose to chop 250 pipe.it looks pretty tight around airbox.you should either make a new sheetmetal airbox or try and find a airbox off another model bike that can be modified so exhaust will fit inside subframe.  500  performance losses with 250 pipe really not a big deal.theory behind 2 stroke exhaust is very simple.there are a ton of books on  how to tune and modify 2 stroke  pipe to give desired powerband.the kx 250 pipe doesnt come out of cylinder and  make the sharp looping turn like the kx 500.kx500 exhaust makes that big loop to increase backpressure for better bottom end.if you use a smaller piece of slightly smaller diameter pipe in 8 in. section you fabricate you can achive similar increase in backpressure [length  and diameter of the smaller section can will determine how much bottom or top end performance will be affected.]

[K5RACER]

Ok now on step 3, Can you please explain to me exactly how you modifiyed the tank? (Plastic strips and chem metal???) Not sure what exactly what you did.

Thanks

[demographic]

Ok now on step 3, Can you please explain to me exactly how you modifiyed the tank? (Plastic strips and chem metal???) Not sure what exactly what you did.

Thanks

I reckon he took a bit out of the bottom of the 250 tank cos the 500 mill is taller

[supermotokx]

Well well well

I've been of on holiday so I'm sorry I haven't replied any of your posts. So let me start by doing just that:

K5RACER: I just posted some more pics of the bike. Unfortunally I got my camera stolen   in which I had almost 100 pics of the bike. So all the posted photos are old ones. I'll post some new ones when I get around to do it.

kxtaz: First thanks for all your ideas and for your offer to weld the pipe for me. However at the time you wrote all the welding was done (and besides that I live in Europe...) - but BIG thanks anyway   . I do think you may be right about using a 250 pipe together with the 500 pipe, but I asked 3 kawasaki dealers and they all suggested turning it, so that was what I did. The pipe is now approx 8 mm longer which gives a little more low end, but I've lost a couple of horses overall. I might consider a new race pipe (Van Hasselt or Jolly Moto) for next year since the race budget for this year supports racing only and the pipe costs 500 $.
 The airbox is now shielded from the pipe with heat resistant material (as is the tank from the engine) and the pipe is now sits a good inch away from the airbox.

Demographic: Yes I cut out a piece of the tank were the spark plug it located. Then I made a new piece using chemical metal, fiberglass and epoxy

[demographic]

I noticed that you have made up a rear sprocket yourself.

You can get front sprockets made by Talon engineering in 10-18 teeth and rears in 38-54 teeth.

Should give you a few options to play around with

[Paul]

WOW!! Can you even get a 17 or 18 on the bike? I know Team Green raced Baja with a 16 up front and would imagine that was a tight fit.

You can get front sprockets made by Talon engineering in 10-18 teeth