Hybrid homebuilt combos

[dxg]

I'd like to build a hybrid woods bike or two by taking a small motocrosser like KX100 or KTM105 and putting a small 125-200cc 4-stroke in it. I'm sure it's been done before, I would like some opinions as to what is the easiest combo fabrication-wise. I'm guessing a KX100/KLX125?  Maybe a link to articles about this type of project? Any suggestions and comments are welcome. Thanks.

[Monaco]

Xr200 in cr125 frame

[William1]

You'd be better off taking a 4S bike and just doing up the suspension. Just because you can does not mean you should. See something like a CRF150B

[nuity5]

Not exactly what you’re describing but this is my hybrid build. It’s a combination that has definately been done before - KX125 chassis with a KDX200 engine. I bought every part off EBay. Personally I don’t like Kawasaki green and like Yamaha blue / white so here it is. I’ve got a complete bottom end on the way to finish frame / swingarm modifications. Clay

 

[dxg]

My basic idea is to make a less than full size bike with good suspension, light weight and a simple, quiet, easy to maintain motor. This would be for the kids and their friends to ride on fairly tight woods trails where a 4S motor would be more manageable and power not a big factor (we don't have mountains in Michigan). So I'd rather not start with a full size CR or KX 125.

The KX125/KDX200 is a cool idea, but I think such a bike already exists, I could just buy a KTM200EXC. And yes, the CRF150 would probably be my choice for a ready-made bike if I didn't want to build one. Or maybe the TTR125.

[76xtdrvr]

Something like this maybe?

 

[nobade]

Just buy an AJP?

[Danceswithtrees]

I wanted somewhat of the same thing as you, a lightweight, 4 stroke, lower seat height extreme enduro bike, for myself.  I opted for a new leftover 2017 crf150rb.  I've done tons of work and mods on this bike but most notable would be getting 18/21" wheels on it.  It's very fast and surprisingly grunty for a little 150, albeit the engine is not stock anymore, but even stock it was fast.  Probably too much for kids unless they're experienced.  Oh and it weighs 198 lbs ready to ride with gas.

[dxg]

49 minutes ago, Danceswithtrees said:

 Oh and it weighs 198 lbs ready to ride with gas.

Yes, that's one of my top goals. Weight is first factor in tight woods. Size is second. 

Do you have a writeup on your crf150 project? I'd be very interested. Very cool.  

[400yzturbo]

I’m building a CRF450 chassis with a 400ex motor.  It’s not easy but one day I’ll complete it.  Attached is a pic of current status other than the exhaust system is completed.

Its not an easy swap, but if people are looking at this topic they may be interested.

 

[Danceswithtrees]

9 minutes ago, dxg said:

Yes, that's one of my top goals. Weight is first factor in tight woods. Size is second. 

Do you have a writeup on your crf150 project? I'd be very interested. Very cool.  

Most of what I did is here

 

[sbest]

Kinda interesting 400YXturbo. Lots of interesting stuff going on in that garage. 

When I was young (1970's) I stuck a 300 single cylinder sled engine in an XL250 complete with CV clutch. Was not a thing of joy to ride. You had to keep a careful eye on not getting your legs tangled up into the belt. Sold it for about what the engine alone was worth.

 

After running a 660 Yamaha Raptor for a few years, I wanted something as powerful, yet lighter and less of an investment than the nearly new Raptor. The answer is my Yamaha Blaster with a nearly 50hp KTM 250 motor. 

It is a kick-ass rig. Rips pretty good, and if I sold it I could get...  ... about what the KTM engine is worth. 

I should mention that it took weeks and a fair amount of cash to put it together. If you haven't done it before, you cannot imagine all the little problems you will run into. The first year of running was more or less constant re-engineering little details to gain reliability. It is fast, pulls wheelies at any speed, light, reliable, and yet it stays in the garage most of the time because most of the time less HP is actually more fun to run with. No fun riding 1/4 throttle all day. 

I suggest if you want a small frame 4 stroke, get one stock. I have a little CRF100 that fits that bill nicely. I use it as a buddy bike for under 200 lbs friends with limited riding experience. There are many cheap and reliable bikes in this category. 

 

 

[Danceswithtrees]

This is one of the best built project bikes I've seen.  TT member stevethe built it using a BBR crf150r frame and xr 200 engine and it weighs in at 183 lbs.

 

[Old Plonker]

12 minutes ago, Danceswithtrees said:

This is one of the best built project bikes I've seen.  TT member stevethe built it using a BBR crf150r frame and xr 200 engine and it weighs in at 183 lbs.

 

Here's another BBR XR200 183lb project.

 

[Danceswithtrees]

22 minutes ago, Old Plonker said:

Here's another BBR XR200 183lb project.

 

I think I got these two mixed up.  The pics of woodsryders bike are all gone so I found steves and posted that thinking his was the one that was 183 lbs.  I've book marked all these build threads and read through them all before I decided to build my 150r.

[teamrude]

XR200 easy and fairly light for a 4t. Easy to make decent power as many parts available. 240cc at 12.5-1 and cam/carb/headwork and quite impressive. CRF230 motor weighs a tad more, electric start only but 270cc easy to build.

[Old Plonker]

1 minute ago, Danceswithtrees said:

I think I got these two mixed up.  The pics of woodsryders bike are all gone so I found steves and posted that thinking his was the one that was 183 lbs.  I've book marked all these build threads and read through them all before I decided to build my 150r.

No pictures? What a shame! Woodsryder's bike is really beautiful: an example of how light and lithe a little air-cooled thumpette can be. The whole thread takes my breath away. The dialog between woodsryder, chuck and swiss is a lesson in the intricacies of building light.

Here's another build that rings my chimes: at one point it was 210 lbs, but then he added more lightness with Ti axles and swingarm pivot. With guys like this, is a project ever finished?

 

[Old Plonker]

3 hours ago, Danceswithtrees said:

I wanted somewhat of the same thing as you, a lightweight, 4 stroke, lower seat height extreme enduro bike, for myself.  I opted for a new leftover 2017 crf150rb.  I've done tons of work and mods on this bike but most notable would be getting 18/21" wheels on it.  It's very fast and surprisingly grunty for a little 150, albeit the engine is not stock anymore, but even stock it was fast.  Probably too much for kids unless they're experienced.  Oh and it weighs 198 lbs ready to ride with gas.

I love your build. You've done everything I have planned for mine, but haven't finished yet, and you've done it all with great care and attention to detail. 

[Old Plonker]

23 minutes ago, Danceswithtrees said:

I think I got these two mixed up.  The pics of woodsryders bike are all gone so I found steves and posted that thinking his was the one that was 183 lbs.  I've book marked all these build threads and read through them all before I decided to build my 150r.

Here's another fairly light build, again from woodsryder: 

 

[dxg]

1 hour ago, sbest said:

I suggest if you want a small frame 4 stroke, get one stock. I have a little CRF100 that fits that bill nicely. I use it as a buddy bike for under 200 lbs friends with limited riding experience.

Yes, I have a CRF100 myself, with a few aftermarket pieces, for exactly that purpose and it does very well. What I'm looking to do is a step up from that. Not a lot bigger, not a lot heavier, not a lot more power (well, I'm negotiable on that one), but an order of magnitude more suspension. 

Some of you guys have done some superb work, both engineering and fabricating these one-off bikes. I'm looking to accomplish a similar goal by "parts engineering" a bike together.  I reason that I should be able to take a KX/CR/YZ 85-100cc bike and swap a 4S motor into it, so I don't have to fabricate as much.