3-speed motorbike



Sep 8, 2008
I laced a Sturmey Archer transmission with heavy motorbike spokes into a 36 hole Schwinn 20" rim. This was fitted with a peddle sprocket. A piece of 1" 4130 chrome moly became the main frame tube and a front 20" fork was inserted in one end and a steering head welded to the other. It also got a
20" fork in the usual manner. A pair of 1/2"EMT conduit tubes were joined with some short tubes to become the mount for the tank and seat. It pivoted just behind the steering head and the rear supported by a pair of shortened front fork legs from a James 125. The motor flanged into a plate welded under the Cr Mo tube The tank and seat were made of fiberglass on styrofoam bucks protected from the polyester resin with water soluble wall sizing. after 1 course of glass was laid, a filler flange with a cap and lid from a Brit oil tank and 2 plates with blind brass door closer mounting nut tubes silver soldered in were placed. the glassing went 2 or 3 more layers and by that time the grinding stuff had made the family laundry :( and my little daughter was sitting in the tub with baking soda from diaper rash. I cut a hole through the glass in the filler neck, I poured in 1 cup of lacquer thinner and SHAZAM, the tank was empty! Some hot water took out the protective coating. The rear of the seat resembled 1/2 of a headlight shell and the tank had a knee-notch. The straight handlebar got a twistgrip for the gears and a compression release lever became the throttle. The jackshaft was welded on top of the Cr Mo tube just in front of the rear fork.
It was equipped with my first ever home-made sprocket, an ally 36 T #35 chain size. I made it with a drillpress and 8" rotary indexing table. My lathe did the OD and tooth front profile. I was so delighted with the result I engine-turned the finish. This connected to a centrifugal clutch. The rear drive was a brake sprocket on the jackshaft. There were no brakes and it freewheeled.
My pilot was 6 by then and the engine originally was in his gokart when he was 2 yrs,4 mos. Since then it had been in a handtruck wheeled minibike of 1/4" sched. 80 pipe. During that time it had a chunk of chrome dinette chair for exhaust clamped in ally to the cylinder and sported a stainless heat shield and picked up a piston carb off an Allstate 125. By the time it got to the new one it had a stuffer in the transfer port, the largest available cylinder with raised port windows, a pyramid reed cage (home cookin) and an 11-1/2:1 comp. ratio removable head made on the drillpress and lathe. It was secured with long studs into the base holes and Allen nuts. Also a cast shroud,needlebrg rod & crank from a light plant. The footpegs were kickstart rubbers on 1/2" coldroll on top of the rear fork. The big problem was when he missed a shift the motor revved unmercifully and THEN engaged. Net result was 2 fruitjars full of S-A salvage before we called it quits. I will post pics if I find them and can figure out how
Keith (trackfodder) Williams
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