2009 CR125AF Flat Tracker

chad.bakken

New Member
Hello. I put up an introduction post a while ago and got nothing soooo... Here's my build thread.

It started with a phone call. A buddy said he had bought a 2009 CRF450 and stole the engine for him J&M framer. I asked about the roller and he all but gave it to me. So there I was, with a complete 450 roller and no reason to have it.

I have raced hare scrambles since I was 4 years old and always had a dirt bike around. About three years ago I caught the flat track bug and bought a XR100 set up for the Maddog class. I out grew that quickly and moved to a '74 Rickman framer with a '73 CR250 Elsinore engine. There isn't much racing here in Va and I decided to sell the Rickman and get another regular dirt bike.

Then this roller showed up.

I raced the XR in the Maddog class along with the 0-200cc class. I like the 0-200 so decided to still with that class. I found a 1995 CR125 that was blown up and picked it up for a song.
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I stripped out the engine and put the rest out back behind the shed
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Once I had the engine out it and knew what I needed to do I needed to work on the suspension done before I could figure out the engine. I found a set of '87 gxsr750 forks for cheap and got to work.

I took the 450 triple clamps and 750 clamps. I pressed both stems out and had to machine the clamps. After machining and honing I pressed the 450 stem into the 750 clamps.
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After the clamps were sorted I couldn't help but do a little mock up.
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Next step was the front wheel.


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Thanks! I appreciate it. I'll post more as I get photos saved to my phone.

Another photo of the forks mounted up.

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I apologize in advance for any grammatical errors. I'm not very good at proof reading.


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Thank you. I started the project in July and finished it last week. It was a fun yet stressful six months.

As for the front wheel I used the stock hub from the 125. I set it up in the lathe and tuned off the rotor lugs.
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I used a Buchanan spoke kit and laced it to a 19" rear rim off a YZ250.
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My son was a big help making sure I trued the wheel correctly.
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Next I had to get the front wheel on the bike.
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Mating the CR125 hub to the GSXR forks meant new spacers and axle were in order. Luckily at work you can make personal items after hours.
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I made the axle out of 4140 steel
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The spacers are 6061
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And then came the handle bars. Being as the Suzuki used clip ons I had to figure something out for bar clamps. An open cnc machine and a couple lunch breaks later I had my clamps.
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They took about two minutes a piece in the machine. I cut them apart on a cold saw.
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I'm not a very good aluminum welder so I had the welder at work help me out.
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Well after I had the clamps welded and put the bars on I was able to work on the rake and ride height.

I used my digital protractor and a floor jack. Again, my son was eager to help.
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Here are all the numbers I got from the set up. I found a write up on setting your bike up for short tracks and got my numbers as close as I could.
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Looking good! Your son is a lucky boy to have you get him involved with bike building :) I did the same with my son just as my dad did with me!
 
That's awesome. I grew up in my dads garage watching him fix our dirt bikes. He isn't a fabricator but is an excellent mechanic. He rebuilt the engine that's in this bike, along with all the bikes my brother and I blew up over the years. I learned a lot from him. My son wants to be a machinist like I am. That's makes me happy but I have mixed feelings about. There are many less stressful professions that earn way more money.


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Once the numbers were in line I sent the stock shock out to be shortened and re-valved. To match the forks.

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I made a little wooden strut to keep the rear end up and started playing with engine placement.

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It amazes me that the swing arm pivot shaft and the rear engine mount were a perfect fit despite being 14 years apart. The 450 frame left a lot of room to play with but I had one major hurtle. The exhaust port.
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chad.bakken said:
That's awesome. I grew up in my dads garage watching him fix our dirt bikes. He isn't a fabricator but is an excellent mechanic. He rebuilt the engine that's in this bike, along with all the bikes my brother and I blew up over the years. I learned a lot from him. My son wants to be a machinist like I am. That's makes me happy but I have mixed feelings about. There are many less stressful professions that earn way more money.


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That's great he wants to be a machinist, keep him interested! I did an apprenticeship in a fab/machine/welding shop and have never regretted it. I ended up getting a degree and working as a mechanical designer after that.
That exhaust port is quite a hurdle, do you have a plan yet?
 
Oh yeah! I figured out where the frame needed to be modified and started cutting.

I started with a 2 1/2" hole saw.
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I cut out the rest and used a carbide burr set to clean it up.
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I cut the pipe and rotated it to get it where it would fit and I could use the stock 450 mounting locations.
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I got everything mocked up and took the frame to work. A little more grinding and making a filler panel didn't take to terribly long and the welder at work helped with the filler and adding a brace across the bottom of the frame.
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Doesn't the service Honda 500AF move that whole piece up for the exhaust? I know you're not squeezing a cr500 in there but it seems like the concept would be the same. I know there are conversion kits floating around the net. http://www.ebay.com/itm/112260643043

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They rebuild the whole lower cradle. That was my initial plan but, being as I am not trying to mass produce or build more, making all the fixtures to do it wasn't worth it. The way I did it I didn't cut into any main structure or high stress area. Just the lower casting. With the added brace it will be just as strong as stock. I don't plan to make another. My next build will have a steel frame so I don't have to rely on other people to help.




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clem said:
I know there are conversion kits floating around the net. http://www.ebay.com/itm/112260643043

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I hadn't seen those kits before. Looks pretty neat. I tried to keep as much of the stock frame as possible. Just enough to get the pipe through. Plus with the 125 that's the only issue. There is a ton of clearance everywhere else. From what I have read Service Honda uses a 250F frame. I'm not sure of the size differences.


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Well... I haven't added anything in a while and have been super busy with other things. So I decided to cut to the case and post up a few finished photos of the bike. I'm heading to South Carolina this weekend for the Sumter national enduro but making a pit stop in NC on Friday to run the bike and break the new engine in.

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