Jump to content
Sign in to follow this  

CR125 Build

Recommended Posts

I just picked up an 02 CR125 motor for cheap and I'm planning on building a bike from the ground up. There isn't a hard timeline set and this is just something to add to my collection, I have my 450 for racing, but I remember my 125 days fondly. I'm planning on taking some pics along the way and was looking for some suggestions on the build. Brainstorming I came up with a couple questions and a loose outline for how I'm going to spend the 1500-2000 (hopefully it doesn't spin out of control) or so I figure I should be able to do this with. This is one of those journey vs. destination deals, where I'm hoping to enjoy the process of putting together the bike I couldn't have in my teens, because YZ's and RM's were easier to find deals on and I couldn't buy certain parts due to financial reasons.

First the questions:

1. Will the motor bolt right into an 07 frame? If so, what about the exhaust, electrics etc...

2. For a guy that is 185-190lbs w/o kit are the CR250R showa forks the only way to go?

3. What should I look out for as far as parts from other year models that will mate up nicely and were improvements between '03 and '07.

My probable parts list:

1. Looking at 134 kit for the top-end. I know it's going to be weird riding a 125 after almost 10 years on bigger models, and I'm not 145 anymore, but I'm hoping a 134 will increase fun factor. Eric Gorr is what I'm looking at...

2. PC Works Pipe /R304 w/ a VForce3

3. Stainless Bolt kit, one off Ebay is already in the mail... Fasteners and nit noid stuff I'm sure will be a bitch.

4. The Renthal treatment, Fatbars, chain, sprockets, I have some spares from a CR250 I had not too long ago, I have to check on the FS, but I think the rest will work.

5. I think I have all the plastics as well, I'll get brand new stuff with graphics after completion, but that will wait until everything else is right.

6. I've got an 02 frame, swingarm and shock that I'll use if the '07 won't work. I'd like to use the '07 because I believe their was an issue with the swingarms from '02-'03.

Thanks for the input. If your wondering why the hell you would bother to read this long post and respond, sorry for the time thievery, but I do promise to post pics as the thing goes.

Take er ease...

Share this post


Link to post
Share on other sites

I bought an '03 a couple years ago as a backup bike. For me getting the handling sorted out was biggest issue. I ended up getting a 1" lowering link for the rear and raised the fork tubes up 3/4" in the clamps. The handling is awesome now. The motor was fast stock but had no low end and would come on all at once. I did a lot of work to get air into the thing along with a VForce reed, ProCircuit pipe etc. and it made a big difference. I'm 195 and it pulls me around quite well. Good luck.

Share this post


Link to post
Share on other sites

Sounds like a great project. That engine will bolt right into an 07 frame, not sure about exhaust but the electrics are probably the same. I personally do not think it is necessary as you already have an 02 frame. Just use crf250r forks and get them revalved. The 134 should be great for your weight, since mine with an fmf fatty pipe and v-force 3 reeds feels like a rocketship, but I'm 125 lbs. Have a great build and post a lot of picks.

Share this post


Link to post
Share on other sites

if you have a 02 frame ther is no need to put on a 07 frame unless your jumping 100ft to flat. As far as front forks i would just get them revaved for your size. and get a set of reeds and a "power now" for your carb and you should be set. also sounds like a fun project. and as far as the 134 kit i dont find nessicary the bikes seem to have nice power and with the mechanical power valve hits harder than the 04+ cr 125s

Share this post


Link to post
Share on other sites

05-07 is mechanical power valves. 04 is a one year only RC valve

Frames will be about the same. They use the same plastic and tank. The showa forks are a nice upgrade to the bike for sure. Think about an oversized rotor also like the CRFSTuff.com one.

For power, google "2001 cr125" and you will find an article on twostrokemotocross that has a lot of info on what can be done to the motor. 05 airboot, drill the airbox, kehin carb, vforce reeds, pipe, exhaust spacer, redo the squishband in the head, port, 7mm power valve pin. Then you can big bore it to a 134 if that doesnt do it for you.

Share this post


Link to post
Share on other sites

I think I might be in a similar place as you (OP) soon with an 02 CR125, so I'll be interested to see your build. Get pictures up ASAP!

Share this post


Link to post
Share on other sites

I recently bought an 02 CR125 that the PC pipe/shorty silencer and V-force reeds. After riding it stock for 1 ride I sent the topend out to get ported and head squish set at .026". I thought about the big bore as well and REP out of springfield Ma talked me out of it. He said quote" if this doesn't do it for you, you can then have the big bore done at a deal". I'm an expert offroad New England guy and weight 230lb.

REP made this bike rip--chugs down low through rock gardens basically won't stall and absolutely rips with a little fan of the clutch. No need for the big bore right off--I think you will be satified with just a port job and head mod--bike is very quick corner to corner and I love horrifying other riders when pinning this bike behind them--HAHAHA

  • Like 1

Share this post


Link to post
Share on other sites

So it's been about a week and a half since this project started. Right now I'm in the components phase, since I didn't start out with a bike and am basically building from scratch. Right now I'm waiting on a fork and set of Tag triple clamps that I purchased to come in, and plan to have a chassis assembled other than wheels this weekend. I'm trying to decide what to do with wheels, and I'm even considering one of the chinese sets of of Ebay, anyone have any experience with those. My other option is going with some used stockers or aftermarket, whatever I can find. I don't have the 1K to drop on wheels at least for now. I am however planning on ordering a VForce 3 and PC exhaust and 134cc cylinder in the next week, putting around the 2K mark so far, but those are loose calculations.

Here is what I'm looking at so far on components:

Frame: CR125R, 2002

Transmission: CR125R, 2002

Forks: 47MM SHOWA Twin Chamber (From an '03 CR250R)

Shock: KYB unit of an '03 CR125

Tag Triple Clamps: Black

Pro Taper Bars and grips that I have already as spares

Plastics are going to what I've got around here until I get the mechanical side perfect, then I buff it out.

Still waiting on my polished fasteners to get here, also might go see a guy parting out a CR near me this weekend to scavenge some nit noid stuff and possible a carb.

Here's my starting point...

IMG_3044.jpg

IMG_3049.jpg

Looking for thoughts on:

Should I split the cases from jump street? The crank doesn't have any play in and seems sound, however, I've never heard the engine run... Since I'm putting a 134 on there I should probably take the hard way and just do it I suppose.

Share this post


Link to post
Share on other sites

cranks are cheap for the 125. It would be piece of mind. Also billet clutch components are going to be needed for the bike since the clutch will be abused.

For the forks, you got the TC units. But not the later 05-07 units that pull the axle back 2mm for increased cornering.

Rims, I have run the DNAs for a while. You get a good set and you wont be sorry. They do have a 1 year warranty.

  • Like 1

Share this post


Link to post
Share on other sites

Is the 07 a 125 or 250 frame? The 3rd gen frames are the same. There nothing wrong with the kyb's, when ya spring and valve them. I have an 06, and both track and trail it, the 139 is a good idea,as is the airboot upgrade. I perfer the rad valve to the v3, the fit is better, and it felt the best out riding. I'm also in the same weight class, and this bike has no problems pulling me around, and hangs right with the 250f's!

Share this post


Link to post
Share on other sites

So I finally got a chance to do some work on the bike this weekend. The project has been simmering for the last month month and half due to work and the season in general. Priorities for time off go to riding first and tinkering second, anyway, here's what's happened. Decided against a 134 off the bat and went with a new OEM cylinder and head. Got a Vertex piston, and VForce 3 Reed Valve, also picked up a Pro Circuit Works pipe in good shape with a stock silencer for cheap. The pipe needs the rust removed though, more to follow on that.

I put radiators on after I snapped the pic, but waiting on new steering bearings before I really start working on the chassis.

IMG_3059.jpg

Ended up getting going standard size first, may go big after the bike is sorted out otherwise.

IMG_3058.jpg

Vertex finding a new home.

IMG_3060.jpg

Forgot how easy working on a bike can be...

IMG_3100.jpg

Engine getting ready to go in the frame

IMG_3104.jpg

Share this post


Link to post
Share on other sites

Great project for a great bike. If you don't mind the noise, I'd get a shorty silencer; a little more grunt, and sounds much better. As someone said before, do the cheap mods first (you don't need a big bore): '05 air boot, a few holes in the airbox, and if possible, a powervalve spacer (I machined one in 20-30 minutes). If you want more power, get the cases stuffed, cylinder ported, a kiehin pwk 38mm airstryker carb, as well as head mods if you don't mind running race gas. Combine all those for a wicked-fast 125. Good luck, and I look forward to the finished product!

Share this post


Link to post
Share on other sites

Thanks, I've already got the PWK airstriker, just have to assembly it, it's currently in a box. I put the motor in the frame, and started setting up controls. I installed a brand new clutch cable and set it to find a clutch pull equivalent to to an 84 YZ490 or something. Makes my KX450F feel featherlight. Thoughts? Also had to replace a seal on the inner clutch cover, so opened it up a little further, got it pretty dryed out inside and reassembled with fresh gaskets.

Edited by Slow250

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×