2002 Yamaha YZ125 Restoration, Part 3

May. 06, 2010 By Ricky Sosebee

Covering our powder coated frame ensures we don’t knock chunks of candy blue off while putting the engine into the frame.

The Boyesen Ignition cover really set the look for our YZ125.

We left off on part two of the Yamaha YZ125 Restoration with our suspension being overhauled with new Pivot Works bearings and seals using our Motion Pro suspension service tool kit. This means that the bike will be going together rather quickly from this point on. After much discussion we decided to install the engine into our beautiful candy blue frame without any internal modifications at this point. Future plans may include a trip to L.A. Sleeve for some serious top-end construction. We have a lot to accomplish so let’s get right to it.

For our engine install, we decided to tape up the frame around the engine bay so none of the candy blue BK performance powder coating would end up on the floor. These little precautions will hopefully keep the bike looking sharp. After setting the engine in place in the frame it was a turning point for the construction of this bike. The wiring had been cleaned from top to bottom and also checked over for any chaffing or cuts that could have occurred during this beast’s lifetime. A new spark plug cap was installed also because of one ominous fracture in the original that could lead to some performance issues.

The Boyesen Rad valve will add ponies to the 125cc powerhouse.

CV4 has made these very trick Radiator hoses for many brands and sizes of motorcycles and atvs.

Before we installed the carburetor there was a priority at hand. Boyesen engineering had sent over a really cool part that was surely going to make the power of our YZ125 just a bit better. The Boyesen Rad Valve is a complete reed cage setup that tunes the air and fuel intake for optimal performance. This device goes into the stock reed cage mount and replaces all of the stock parts. The Rad valve will make a smoother throttle and better roll on power over stock. These Boyesen Rad valve setups have also been known to make better power that allows for taller gearing. This should add some excitement to our test ride!

After getting the Rad valve installed I dug a bit deeper to find the Boyesen Factory racing ignition and clutch covers we had ordered to add just the extra bit of class to our rig. These covers replace the factory ones perfectly and with the raised, bright-cast-aluminum lettering against a durable black-powder-coated surface they really look trick. As if awesome performance wasn’t enough to engineer at Boyesen, these guys are just as concerned with perfection and looks as well. 


The Adaptor from Moto-Master allowed us to use the over sized flame rotor by raising the caliper.

The Moto-Master adaptor is a must have for getting the bigger rotors on most any MX bike.


So the engine is in and mounted. We have our new Rad valve installed as well as our trick engine covers. The next order of business was to be sure and get the radiators mounted. The brand new Yamaha factory radiators were a blessing in disguise, as the old radiators had been beat up pretty good. With collapsed sides and cracks that spewed antifreeze when over-heated, this was a must do as well. The OEM parts are hard to beat and for a perfect fit, this is where I knew I had to shop. I didn’t, however, want to just put the new radiators on without any type of protection, so I searched and found some body armor for the new radiators.

Works Connection has many protective parts for your off-road needs, and when I spotted the radiator braces I knew I had to have them. These braces are only $59.95, and when compared to a very expensive radiator that’s like money in the bank. The CNC-cut 5052-grade aluminum is shaped to reinforce the radiator and this simply bolts on under the stock plastic. I’m building this bike back to ride and I also want each part to last as long as possible, so adding little things like these braces are just insurance for me. My shopping trip didn’t end with just the braces though, as Works Connection also had frame protection and an engine skid plate to top off the protective items for my YZ. The frame protectors add a smoother, flatter surface for more grip and control of the monster. Not to mention, it also protects the frame from chaffing. These frame guards look trick, and with all the hardware included to mount them these were an easy install.

Moto-Master flame rotor is oversized to optimize stopping power and with new “race” formula pads there will be stoppie’s galore.

This Works Connection skid will keep the bottom of my engine safe.

The frame and engine will also get some good protection from the Works Connection skid plate. Unlike the other two protective pieces, this skid plate is made from 6061 T-6 aircraft grade aluminum. This thing is tough, and for the bottom of the YZ 125 that’s what I need. The precut oil drain hole will also allow me to change the engine oil without having to remove the skid plate. The skid does cover the frame rails but doesn’t extend past the rails. I’m not sure if that would be enough coverage in cross-country type racing, but the guys at Works do have case guards should I need them later. Well, we have a lot of protection going into this Yamaha YZ125 restoration, and that’s great because I want this machine to last for many more years.
Getting back to the radiator I now needed to install my rad hoses. When I say “rad” that’s what I mean. The company known as CV4 is located in North Carolina, and just one of their specialties is replacement radiator hoses for motorcycles and ATVs. They offer colored radiator hoses that are not only great to look at but are very functional as well. The hoses are made of quality silicone construction with braided layers to strengthen the hose. Our hose kit is very close to Yamaha blue and was a simple fit in the factory positions. These hoses feel tough and I have heard only positive things about their reliability. I just need to find some trick clamps to finish the look.


The left side Works Connection frame guard simply bolts on using the sub-frame and chain roller bolts.

The right side Works connection Frame guard bolts on using the rear brake reservoir bolts.

With the engine compartment almost finished and just waiting on a few extras, I decided to move on to the brakes and braking components. The fluid in the brake system was totally drained when I disassembled the bike but nothing had been cleaned. I took the front and rear master cylinders apart and rebuilt these with new seals. The calipers had also been neglected for a while, so a quick once over and thorough cleaning left these functioning better than before.

The next item had to be the discs on both the front and rear of my YZ, as these were in rough shape. I decided to go with a company called Moto-Master that builds quality braking components for Yamahas. I bit the bullet and went outside my renovation budget to get an oversized front rotor and caliper adaptor from Moto-Master. This wave-style rotor not only gives me more braking surface, but with the Moto-Master brake pads this combo is going to get us stopped in a hurry. When replacing front or rear rotors there should always be new pads installed. Old or worn pads take longer to seat on the rotor and could create problems while being used. The adaptor for our front caliper was very easy to install and it utilized the stock mounting holes to raise the caliper to make room for the larger rotor.  It is always good to use new rotor mounting bolts when installing a new rotor. This just adds more insurance to the ride. Also, adding a bit of blue loctite on the threads will keep them in place.

The Boyesen Factory team clutch cover adds even more class to this Yamaha YZ.

The Moto-Master brake rotors are made for high-speed stops and the race formula pads add better stopping power.

The 2002 Yamaha YZ125 has been quite a fun rebuild so far, and in next month’s final installment we will be adding the finishing touches as well as ride this bad boy for the first time in over a year. Now, we realize you might not have a year to wait to go riding, so strip the old bike in the corner of your garage down and get to work. Being patient is yet another difficult thing to overcome, but I’m sure that once we get this bike back together it will last for many more years. Buying the parts along will have a lower impact on the wallet! So stick with us as the restoration of this motocross icon continues.

Works Connection has many products to help you protect the ride and these Radiator guards are a must have.

Parts List:
Boyesen Engineering:
Boyesen Rad Valve: Part # RAD-33G
Ignition Cover: Part #SC-33B
Clutch Cover: Part #CC-31B

Works Connection:
Center Skid Plate: Part # 10-216
Frame Protectors: Part # 15-231
Radiator Braces: Part # 18-072

Silicone Hose kits: $93.67

Front oversized rotor: Part # 111034
Rotor/Caliper adaptor: Part # 211007
Front/Rear Brake Pads: Part #’s
Front: 0934-12: $36.95
Rear: 0918-12: $36.95
Rear Wave Rotor: 110227: $137.95

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