My first build

Here are a few images of my first motorized bicycle build. It would have been a lot cheaper to buy a kit but nowhere near as much fun.


Bicycle Specifications:
• Frame: Raleigh Venture 3.0 Hybrid
• Rims: 26” Velocity Psychos (36 hole)
• Hubs: Velocity ATBs
• Tires: Schwalbe Marathons 26 x 2.0

Drive Specifications:
• Engine: Honda GX35 4 stroke with a GX31 piston
• Gearing: Double reduction with a ¾” “L” type, timing belt primary (18 tooth pulley at the motor/70 tooth pulley at the transfer shaft) and a #35 chain secondary (12 tooth sprocket at the transfer shaft and a 60 tooth sprocket at the rear wheel)
• Mounting platform: ¼” aluminum plate with ½” x 1” aluminum tube support frame.

The top speed on flat ground is around 27 mph. Since I added the GX31 piston I have more low end torque so I may increase the number of teeth on the small secondary sprocket from 12 to 14 which should give me a cruising speed closer to 35 mph. According to the local police my first drive gear configuration reached speeds of 37 mph. I slowed it down to try to make them happy. Since it doesn’t look like I will ever make them happy I think I will kick it back up.

Thanks TexasDav
It has a Stanton centrifugal clutch but I am considering adding a freewheel rear sprocket just to cut down on the drag should I have to pedal it.

The first gear I used was solid steel and weighed 14 lbs. Here is a picture. Even after drilling the lightening holes once you got it rolling it wanted to keep on going. The bike had to lean up against something because the weight of the gear wouldn’t allow it to stand on its kickstand.

The current gear is hardly noticeable. I had it made out of aluminum and it weighs less than two pounds.

Roadkill said:

This is a very nice design and makes me anxious to produce a couple of my first rigs centered like yours is. Is this thing fast on the slope and sluggish on the up? I am new here and wondered... Are those gears sold by dealers?

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It was a little slow on the hills but in Phoenix we don't have many hills to deal with. I have replaced the 35cc Honda shown in the picture with a 50cc Titan from ThatsDax.com. (See add in upper left corner of this page), now it halls ass up hill, or down. I built an add-on muffler to governor it down to a maximum speed of 32mph on flat ground. Anything over 20 MPH is illegal here anyway. It works by creating back pressure as the engine rpms increase. Between idle and around 5000 RPM there is little to no restriction so I have a great hole shot and plenty of low end torque. Above 5000 RPM back pressure begins to build limiting the engines speed.

I have it torn down right now. I had to replace a couple of damaged spokes. When it's back up I will post pictures of the setup with the new motor. I wish I would have known about the Titan before I bought the Honda. I really like this engine.

The small pulley mounted to the motor is off the shelf. I bought it at econobelt.com. It’s a 21 tooth “L” type timing belt pulley, part number QPELS75020F16. The larger pulley is a 70 tooth “L” type timing belt pulley. I had it custom made out of aluminum at a cost of $307.00. The only pulleys available that size are made of steel and weigh 15lbs. I can provide you with drawings and contacts for having one made if you decide to go that route.

The chains and sprockets are standard #35 3/8” pitch available at any number of places. I purchased mine at McMastercarr.com. The small sprocket on the drive shaft is a 12 tooth and the larger one on the rear wheel is a 60 tooth. They’re inexpensive and last forever.

There are many less expensive methods for building a motorized bicycle but this was fun and it runs great.