When I was 15, I built a motorbike..
When I was 15 years old I built a motorbike by figuring out a way to bolt an old Briggs & Stratton lawnmower engine to the frame of a very used stingray bicycle — with a banana seat! — I bought from a kid for five dollars with my lawnmowing and babysitting money.
I took off the pedals and cranks, and drilled two holes into the tubes that formed the “V” on either side of place where the pedals should have been, about 1/4 way up, and bolted on an L-shaped angle iron I cut to the right length with a hacksaw. This created a little “shelf” on which I could rest one side of the engine, with the horizontal shaft of the engine poking through to the other side of the bike. I couldn’t afford a centrifugal clutch, so I just used a fixed pulley on the shaft.
The good news was that because I had to reverse the engine “back to front” — the crankshaft spun counter-clockwise so I needed to put it on the left side of the bike — the muffler was now in the front and I avoided burns on my inner thigh!
Now I had to figure out how to drive the back wheel.
I knew that washing machines and dryers had large pulleys, so I scoured the neighborhood for someone throwing one away — it was a relatively common occurance to find one at the curb on garbage day — and after a while… success! I dissassembled a discarded dryer and got my pulley.
To attach it to the back wheel I needed to saw each of the ‘spokes’ of the pulley and remove the hub. That way it could fit right next to the wheel without interfering with the rotation of the wheel hub. I ended up drilling holes in each pulley spoke and placed blocks of wood on the other side of the bike wheel — one block for two of the spokes, three blocks for six spokes — and used toggle bolt screws to create tension between the blocks of wood and the pulley to hold it in place.
A twist grip bike gear shifter replicated the typical twist grip accelerator of the motorcycle, by connecting the cable of the gear shift to the carborator.
My mom wanted to make sure it had brakes, so I installed a front caliper brake and hand lever on the opposite side of the twist grip. This was largely for show as it woulld have never been able to stop the machine at speed. I bought a fan belt from the local gas station and connected the rear and engine pulleys.
But how to make it go? I couldn’t use the pull cord to start the engine because the shaft was fixed to the rear wheel and it wouldnt turn, or turn over (a centrifigal clutch would have solved that problem, allowing me to start the engine in “neutral” and using the accelerator to engage the back wheel, but — and yes it was a big source of frustration — I couldn’t afford one)
But I knew that you could push-start a manual transmission car, so I flipped up the choke, pressed hard down on the seat and ran like hell. When the engine caught and was about to start, I would quickly jump onto the bike and GO! Stopping involved shutting down the engine and coasting to a stop.
Interestingly, the angle and weight of the engine made the whole thing list to port when jumpstarting the engine, but once the wheels were turning under power, it was well balanced.
I spent hours driving this thing. The rule was I could not leave the block, so up and down, up and down, up and down I went: Jumping on, accelerating, decelerating, turning and repeating the pattern. Every few rides I needed to tighter the toggle bolts on the back pulley, and perform some engine maintenance. When I was 16 my parents, who really could have used the money for other things, gave me my first motorcycle, a 50cc Yamaha Drop Frame. I’m guessing it was an investment in my safety but, now, as a parent, I know my reaction to the gift was probably priceless at the time. The bike was relegated to a shed in the backyard for a long time, gathering dust, and eventually, and quietly, disposed.
