Building from the ground up?

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7/30/2017 1:34 AM
Edited Date/Time: 7/30/2017 1:36 AM

Skip to bottom for TLDR version

I've been toying with the idea of building a steel ftame yz125. The perfect bIke would be an 01 as that's the first bike I ever raced and I loved the look of the Yamaha of troy bikes back then. Looking around and as discussed in the moto forum used 2t bikes in Colorado fetch a premium. So I started checking ebay and found frames for $150 and swing arms for $50-150. If I bought one to build I would replace nearly everything anyways so I'm thinking why not buy a frame and start there? So my question is this. Has anyone ever went that far? And I've heard most parts from 97 to current are interchangeable is that true? I can rebuild most everything on my bike myself minus splitting the cases (which I'm about to do on my kx250 with a friend showing me how to not screw it up) so I have most of the technical knowledge just curious how difficult it's going to be to source literally every single part. Ideally in the end the bike would look like an 01 yot bike with 01 plastics and every thing (not a huge fan of the modern design) but hopefully with modern A kit with triple clamps, modern shock, yzf swing arm conversion, talon hubs with A60 (or something similar) and a fairly stock motor with a pipe and silencer. So as you can see no nut bolt or bearing would be untouched but can this be done to a 97-01 frame or would it be way to much trouble. I know most if not all can be done to an aluminum frame but I would really rather build an 01 steel maybe an 02-04 if that would be simpler.

TLDR version
I want to build an 01 yz125 without buying a complete bike first with:
01 plastics with yot graphics
Yzf swing arm conversion
SSS or A kit Suspension with nice triple clamps
Nice wheelset
Rebuilt srock to slightly improved motor.
And I want to order each individual part. Would you undertake a build this way?

Typed from my phone, sorry if I screwed up some grammar/run on sentences.


7/30/2017 1:47 AM

Little build background on me. This my kx when I got it.


This eventually happened


Stripped it down


Striped it down and replaced every bearing and had the frame and swing arm powDer coated.


And back together


So I'm no stranger to frame up builds just not sure if the build I want to do is possible or if sourcing every part like carb, wiring harness, ignition, and things like that would even be worth it in the end vs buying a complete bike.


7/30/2017 1:56 AM

How confident are you that each part you might need is available as OEM? There's bound to be a whole bunch of parts that have no aftermarket equivalent and sourcing all those parts new or 2nd hand could be difficult. Good luck if you decide to try it though. Interesting approach!


7/30/2017 2:59 AM
Edited Date/Time: 7/30/2017 3:06 AM

That was kind of my question lol. From most of what I've seen it looks like everything is similar/interchangeable from 97-current so I would imagine nearly everything would be able to be sourced new if needed. I know there was an obvious update in 02 then the frame in 05 but it seems mostly cosmetic from what I can tell. I'm mostly curious if anyone has tried newer parts on an 01 frame with success. Like if I find an 05 plus engine will it bolt into an 01 frame? Or sss/a kit forks and after market triple clamps fithe a steel frame or did the steering stem get longer or shorter or something barely noticeable that would trip me up in the build


7/30/2017 7:23 AM

It's possible and not hard to do. But it would be really expensive to not start with a donor bike at least.



7/30/2017 2:27 PM

I wouldnt buy new parts individually. Start with a clapped out bike and then do a tear down and build up of every part. Buying a whole motor is more costly than rebuilding one. Ive been rebuilding bikes like this for 5 years now and imo definitely the way to go.

The biggest thing is to buy a bike with a good motor. Buying blown up bikes is sketchy because you dont know the interior of the cases.


2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

11/6/2017 4:41 PM
Edited Date/Time: 11/6/2017 4:42 PM

Didn't think a new post was necessary so I'm bumping this one. So I've been researching the best way to build my dream bike and I came across some simple info I missed before. In 05 or 06 they totally redesigned the yz125 motor and it's pretty unanimous that it is better than anything before it. My question is does anybody know if the new motor will bolt into a steel frame? I still want to build an "01" style bike but I want it to be the most bad ass 01 minus titanium for now. So is the modern motor with the 6 speed that much better than the 01 motor with 6 speed? And can you swap them without serious frame modifications? I know the aluminum frame is the same basic geometry as the steel but can't find anything about the motor mounts and location


11/6/2017 5:33 PM

This sounds like a cool project, good luck whichever way you decide to go !


11/7/2017 4:54 AM

Not a bad idea, but your biggest issue will be sourcing cases and misc parts. You might have to buy a lot of new parts, or a donor bike and recondition them.

You will spend more than the bike is worth, as a forewarning.


If you're not mixing gas, you're not haulin ass.

11/8/2017 1:36 AM

No matter what I'm going to spend more that it'll ever be worth lol. It is the first bike I ever raced so there is sentimental value. But nobody knows if an 05 plus motor will bolt into 99-01 frame?