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Thinking about building a kdx/125 hybrid

sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
The more time I spend on my KDX the more I love riding. The more time I spend on the KDX forums, the more I want to build a hybrid. I'm thinking later this year (winter) I'll start building a KDX hybrid - a kdx200 motor stuffed in a 125 motocross bike (CR/KX/YZ/RM125).

reasons:
- I love the KDX 200 motor/power
- everyone who's had a kdx hybrid says it's the best of both worlds for trail riding: kdx power/torque with the flickability/ergonomics/suspension of a motocross bike.
- it sounds like a fun project

SO, I'm on the lookout for the following:

- a 2001+ 125 mx bike minus the motor (CR/KX125)
- a kdx 200 water-cooled engine ('89+)

I'm not in any kind of hurry, since I want to ride this summer, not wrench. But I'd like to start collecting parts now. Let me know if you've got any leads on any of these parts.

Here are a few pics for motivation:

2003 cr125 conversion:
03%252520cr125.jpg


03%252520cr125%2525202.jpg




2003 kx125
03%252520kx%252520125.jpg


2004 kx125
2004%252520kx125.jpg


and another kx
2005%252520kx125.jpg
 
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Greg

Greg

I run a tight ship... wreck
Admin
Location
Grand Junction, CO
That does sound like it would be an amazing trail riding bike! I've spend some time on a KDX 220, it was a fun bike. Do the bigger KDX engines fit into the MX frames?
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
I dunno. The KDX220 and 200 are almost identical, so they both fit into the 125s. I don't know a thing about the bigger kdxs.
 
Corban_White

Corban_White

Well-Known Member
Location
Payson, AZ
You know the MX 125 bikes (all MX bikes for that matter) have a pretty tall seat height, right? 39.3" for the yz, 37.3" for the cr, 37.2" for the kx, 37.4" for the RM. Just for reference, my ATK has a seat height of 36.4". I know that was an issue for you at one time. If it still is then I need to get you out on my wife's bike. If the tall seat is no longer an issue than it sounds like a great project! When are we going to get Chet out? He said the kids had a great time last night. I would be more than happy to bring my wife's bike out for you to try. Tuesday afternoon?
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
I have 2 hours tuesday before scouts, I could swing by and check it out.

Seat height used to be a problem for me. I bought my kdx with 2" kouba lowering links. Those lasted for one ride, while I gained confidence on the bike. Then I swapped 'em out and I'm at stock height. It performs so much better now. I'm getting used to the taller seat height. I just had to ease into it and get used to it.

KDX seat height is 36.2 and while I can't tip-toe on it, I can still ride it comfortably. I think I could go up to about 37" or so. I'll have to ride a cr125 before I decide to go for it. 39.3" is definitely too tall for me right now.
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
I've ruled out the yz's for two reasons:

1) seat height
2) the rear swingarm is hollow, and it can't be trimmed down as needed without MAJOR modification

I think I'd like an '04 kx 125 for the donor.
 
YOUKNOW

YOUKNOW

Well-Known Member
Location
South Jordan, UT
Greg said:
That does sound like it would be an amazing trail riding bike! I've spend some time on a KDX 220, it was a fun bike. Do the bigger KDX engines fit into the MX frames?
Click to expand...

I have a buddy in St. George that stuffed a CR500 engine into a CR125 frame. I guess he had a really big shoe horn? And some welding...


I think that you are on the right track Steve. That sounds like a killer project. Are you planning on keeping it street legal or not? If you like the flickability factor as mentioned in your first post, having all of the street legal stuff off of the bike will make it lighter. Just a thought.
 
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sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
Still not sure on the street legal question. I'll probably get a kit just so I can ride it up the canyon and back without having to trailer it.

I'd have to sell my xt225 (street legal) to afford this build, and I'd like to have at least one street legal bike.
 
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Diesel and Dust
Supporting Member
Location
Smithfield Utah
The KDX hybrids are pretty cool if you ask me :cool:

I'd look into any mid 90's or newer RM chassis especially if you can find a 96-98 with the 49mm Showa conventional forks :chris:. The RM's are killer on the trail and I think the chassis would match that motor very well. Personally I fell in love with the latest Honda 2T chassis (02-07) and in the long run ended up buying one for the handling. You'll have to try my 02 CR out one of these days (hopefully sooner than later lol) and see what you think.
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
I would love to try your '02 CR. Is it a 250 or a 125? Is there a big difference in size between a cr250 and a cr125?

Are the '99 CRs decent? THere's one on KSL with a blown motor for $350. I'll snag it up if the ergos/suspension are comparable to the '02-07s.


I've never seen a KDX motor swap into a suzuki, I wonder how it'd do. My main concern would be the swingarm.
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
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Diesel and Dust
Supporting Member
Location
Smithfield Utah
sixstringsteve said:
I would love to try your '02 CR. Is it a 250 or a 125? Is there a big difference in size between a cr250 and a cr125?

Are the '99 CRs decent? THere's one on KSL with a blown motor for $350. I'll snag it up if the ergos/suspension are comparable to the '02-07s.


I've never seen a KDX motor swap into a suzuki, I wonder how it'd do. My main concern would be the swingarm.
Click to expand...

Size is pretty much the same between the 125 and 250 as far as i know I don't think it is more than a half inch either way.

I like the 1999 (first gen aluminum frame 97-99) CR's, but a lot of people don't. They are extremely rigid to the point you feel like you are riding a brick and it makes for a bike you don't want to ride for a long period of time especially on the trail. I'm ok with them and I think good suspension work can fix most of it, but they are not nearly as forgiving or as nimble as the 02 and newer chassis. That said there are 3 in our group and those guy's never complain about the ride... But I don't think they know any better :hickey:

As for the RM chassis I think it would do great. Most people credit the RM's handling but it's definitely something you'd have to decide. I've seen CR500 motors swapped into RM's, but not a KDX :D
 
sixstringsteve

sixstringsteve

Well-Known Member
Location
UT
Any experience with the 99-05 kx bikes? How do they compare to the 02-07 crs as far as handling and ride characteristics?
 
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Diesel and Dust
Supporting Member
Location
Smithfield Utah
I liked the 94-98 KX's and that's what I rode a lot of in the late 90's. They had a killer motor in general and I liked the perimeter frame. I don't have much experience with the 99-02's or any with the 03 and newer KX's to make that call. I really think you'd have to ride all of the big 5 to their full potential and put in a lot of miles to make a fair comparison :D
 
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