Adapting YZ80 Forks to Your TT-R 125L

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The stock TT-R forks are flimsy, flexy and too weak for serious backyard motocross. They can be made plenty stiff with BBR springs, heavier oil, and a higher oil level, but they are not rigid enough and lack the travel of YZ forks. If you perform the mods below, I guarantee you’ll LOVE your TT-R!

Note: The mods below assume you have the “L” version (big wheel version with disc brakes). If you have the small wheel version, you’ll need additional parts, like a complete YZ front wheel, brake master cylinder and caliper, and perhaps more. Since I only performed the conversion on the “L” model, I cannot say for sure what needs to be done on the small wheel version.

If you have any questions on the conversion, feel free to send me an e-mail. I would be glad to try to help.

Parts needed:

• Complete front forks from 1993-current YZ80
• Top and bottom triple clamps for YZ80. The steering stem from TT-R should be used.
• Front axle from YZ80, part #: 4ES-25181-00-00
• Front fender from YZ80
• Longer front brake line (see below)
• Fork guards from YZ80.
• BBR swingarm
• BBR Heavy shock spring

Custom work:

• Use washers to move the front brake caliper away from the forks (towards disc) approx 3mm
• A washer will be needed (approx 3 mm) on the end of one of the wheel spacers. The TT-R wheel is just slightly narrow for the YZ forks. You may be tempted to just cinch down the axle without adding a spacer, but it will bind the forks.
• Grind off the welded-on nut from the choke bracket and mount the choke bracket just beneath the number plate tab.
• To route the front brake line CR-style, buy a guide that bolts to the front number plate. The OEM upper guide will not fit aftermarket triple clamps. The lower brake line clamp from the TT-R should be mounted to the fork guard.

General notes and suggestions:

• The conversion is basically a bolt-on with a little custom work. The TT-R front brake caliper and front wheel will bolt right onto the YZ forks, they just need some spacers to make them fit the wider YZ front end. But, as with any project like this, the devil is in the details, and hopefully my trials will save you some time and money.
• The YZ forks are about 4” longer than the TT-R. They are positioned in the YZ triple clamps slightly further apart than the TT-R, necessitating the longer YZ axle and spacers on the brake caliper and axle. The axle diameter on the YZ and TT-R is the same.
• A longer brake line is needed, but the YZ brake line won’t work because the fitting at the master cylinder is different. If you want to use a YZ80 brake line, you’ll also need a YZ80 master cylinder. I opted for the deluxe setup and bought a 2001 CR250 master cylinder and Fastline brake line. The brake line bolts right up to the TT-R caliper. This is actually cheaper than going with the YZ80 setup, and provides better braking power. One other option is to have a custom longer line made that will fit the stock master cylinder. A 1997 CR80 brake line bolts right on to all the stock TT-R stuff, but I could never get it to work quite right.
• Your options for the lower triple clamp are numerous. The cheapest and cleanest way is to buy an aftermarket unit for a YZ80 without the stem. Then swap the TT-R stem and bearing from the stock TT-R clamp to the YZ clamp. The YZ stem is the same diameter as the TT-R, but longer, so if you buy the OEM or TAG assembly (sold as clamp and stem together), you’ll need to make some spacers. I used Performance Engineering clamps top and bottom with the TT-R stem for a perfect fit.
• The TT-R front fender will fit the YZ triple clamp, but drilling new holes is necessary, and it doesn’t fit real well. A UFO YZ80 front fender is the best way to go (especially since it’s under $25). You’ve spent enough money already on this project, why not finish it off right?
• Buy stiffer springs for the YZ forks. I used Race Tech’s .33 kg/mm springs with 7 wt fork oil 75mm from the top. The stock springs are .29 kg/mm with 5 wt oil 90mm from the top.
• The stock TT-R shock will be fine, but a heavier spring (BBR) is necessary to balance the ride. A BBR swingarm is needed to offset the increased height of the front end. To my knowledge, aftermarket shocks for the TT-R are standard length and do not increase travel or seat height, but they do offer a better ride. If you don’t get the BBR swingarm, your bike will handle like a Harley chopper.
• The forks on the YZ80 have been externally the same (save color) since 1993. This means that any YZ hardware you buy can be from any year of this series. The newer the forks the better, though, as Yamaha upgraded the internals over this time period.
• If you get your forks from a salvage yard, they probably won’t come with the guards. OEM fork guards will run you $100. I opted for Maier units (the only aftermarket available for the YZ80) for under $30 a pair.
• If you’re running the BBR exhaust, the front tire will rub the header when you bottom the forks. This is not a big problem, and can be minimized by running the forks as far down in the triple clamps as you can, and making sure the exhaust is properly mounted and fully inside the manifold.

Cost

• For everything above, just under $1,200 (remember, this includes the $400 BBR swingarm). This assumes you pay $300 for the forks from a salvage yard and do some price-shopping for everything else. If you’re serious about your playriding (?), it’s money well spent, and will save you from other damages to the bike (bent wheels, cracked frames, etc.).

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Disclaimer: Don’t do anything stupid, and if you get hurt it’s your fault, not mine J