2000 kx125/hybrid questions.

Discussion for swapping a KDX motor in a MX frame...
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gwynfryn
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2000 kx125/hybrid questions.

Post by gwynfryn »

I need to pick your brains .

I'm considering going down the hybrid road and for sale near me is a 2000 kx125 with a seized motor. It has no front end as this was used on a kdx fork swap, it looks well used but is very cheap.
The bike would be raced cross country and enduros at a fast intermediate level and will replace my 06 200.

My main question before I even look at the kx is what are my fork/front end options?. What would be the best and most straight forward application? Will 2003 and on kx forks fit, or what about kxf and rmz forks? . If I stick with kx forks can i use my kdx rotor and caliper and front wheel?. I will get the suspension rebuilt/valved to suit my weight(75kg) and riding conditions(not mx).

For those that have a hybrid how do the kx125 radiators cope with slow ,tough, mud conditions. any over heating issues or do the radiators have a similar volume , just no overflow reservoir.

One more question(for now) - it appears that some have pipe clearance issues with the down tubes where it exits the cylinder and others don't. Is this generally a matter of how the motor is mounted (tilted on the swing arm mount) ,the type of pipe, the year of kx , or are all the frames slightly different ?

Thanks.
Last edited by gwynfryn on 07:24 pm Mar 12 2014, edited 1 time in total.
ecojbr
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Re: 2000 kx125/hybrid questions.

Post by ecojbr »

The 03-05 forks fit almost directly, you will have to make minor adjustments to the steering stops. As far as radiators, you will never over heat the bike. I myself and my wife have been racing my hybrid for 3 years. So it WILL handle both faster and slower riders with ease. I have built three now. One for me, two for customers. A 01, a 03 and an 05. Only one had pipe issues and a simple torque ring inside the cylinder where the pipe goes into the head fixed it right up. Take off with your build, you will absolutely LOVE it. Transformers it into a whole new bike.
04 kx220 hybrid
03 kx 250
05 kdx 200
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bufftester
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Re: 2000 kx125/hybrid questions.

Post by bufftester »

All of what ecojbr said plus the following (based off my experience building my hybrid which is a 2001 KDX 220 motor in a 2001 KX125 frame)

My main question before I even look at the kx is what are my fork/front end options?. You can make anything fit given enough time and money. There are KDX's sporting KX, RM, CR, Marzocchi front ends. The process is pretty easy-most involve just pressing steering stems to fit. Most of that is covered in the fork swap forum

What would be the best and most straight forward application? The most straight forward is a 1999-2002 front end (all L-models) There are some little things to be aware of.
  • 1999-2001 are all the same for both the 125 and 250 (main difference being that the 250 upper triple has rubber mounted handlebar mounts, the 125 is hardmounted)
  • In 2002 the fork diameter changed, so the triples also changed (and the 125 got rubber mounted handlebar mounts)
  • 2003-2005 KX front ends will fit with some spacer work. Same for the KX-F
  • Regardless you'll need the KX front wheel. The KDX hub will not work with KX axles. You can see if RB is still doing the KX axle mod to allow a KDX wheel for an option.

I used 2000 KX250 triples, with 1999 KX250 fork legs and a 2001 axle. If you are a heavier guy look for the KX250 forks as they come stock with a heavier spring. (My entire front end was bought on ebay for under $200)


Will 2003 and on kx forks fit, or what about kxf and rmz forks? Yes, with work. See above.

If I stick with kx forks can i use my kdx rotor and caliper and front wheel?.
  • You can use the KDX caliper, but you will need a KX wheel/hub, or
  • You could get a KX hub and then lace your KDX rim to it, if you felt inclined, or
  • Another option is a modified KX axle by RB Designs which allows you to run the KDX wheel (including the Odometer drive) with a KX front end.

For woods riding I would recommend you also route your brake cable as it is on the KDX and not under the fork like the KX. Again, lots of info in the fork swap forum.


For those that have a hybrid how do the kx125 radiators cope with slow ,tough, mud conditions. any over heating issues or do the radiators have a similar volume , just no overflow reservoir. I am using 2005 KX250 radiators on my hybrid, they bolted up directly. You end up using a hybrid mix of KDX and KX tubing to plumb it together.
  • Initially I was trying to find a spot to mount the overflow bottle from the KDX, but its was a hassle so I ditched it. I ride in the Pacific NW in some very technical places and have never overheated. Not saying it can't happen, but if it did I'd lay even money that you'd be overheating the KDX in the same conditions.
  • The radiator volume is about the same between the KDX and KX (just under 1L) but the hose routing is a little different as the KDX routes coolant up through the right radiator and down through the left radiator so that all coolant passes completely through both radiators.
  • The KX routing runs coolant into the bottom of the right radiator as well, but the right and left radiator are connected with hoses at top and bottom. The coolant exits the top left radiator, so in effect you are running half the coolant through each radiator.

As for which design is more efficient I haven't a clue, but they both work well.


One more question(for now) - it appears that some have pipe clearance issues with the down tubes where it exits the cylinder and others don't. Is this generally a matter of how the motor is mounted (tilted on the swing arm mount) ,the type of pipe, the year of kx , or are all the frames slightly different ? This is primarily tied to your placement of the front motor mounts. Some aftermarket pipes are slightly different from each other and from the OEM unit.
  • From what I have seen the frames don't vary much, its more the difference in aftermarket pipes. Best way to work with it is to mock up your entire Intake/motor/exhaust before welding any mounts. Very important because if you don't rotate the motor far enough forward you will have fit issues with the carb and air box.
  • I used the stock pipe and 3 copper crush gaskets and had no fit problems.
  • And of course you will have to fab all new exhaust mounts (not difficult)

My build is linked in my signature, Lots of good info in the Hybrid forum.
gwynfryn
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Re: 2000 kx125/hybrid questions.

Post by gwynfryn »

Thanks, that helps heaps. I think I will take the plunge!
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