Motorize A Bicycle
There is nothing new about mounting a small engine to a bicycle. Long before today's liability laws, major bicycle companies sold kits to motorize bikes.
Motorized Bicycle History
American-made Whizzer introduced their gas-engine bicycle kit in 1939, featuring a 138cc four-stroke engine and belt drive. During World War II, motorized bicycles became an inexpensive means of transportation during a period of gasoline shortages and limited automobile production.
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After the war ended, Whizzer and other companies became popular with kids looking for more speed from their heavy bicycles. In 1949, the company introduced a complete production bike, called the Pacemaker. Sales of the Whizzer conversion kits continued until 1962.
By this time, mechanically-inclined teens had gotten the bug, and started removing engines off old lawn mowers and doing it themselves.
Best Type Of Bicycle To Motorize
Most gas-powered bicycle motor kits are designed to fit 24", 26", or 28" wheel bikes with a V-frame. The most common are 26" cruisers, road bikes, mountain bikes, city bikes, and beach cruisers.
Measure Frame For Engine Clearance
To find out if a bicycle would be a good candidate for a motor, do a little measuring. Two-stroke gas engines are about 8.5" in height, 7" in length, and 5" in width. To mount the engine, the frame should have 9" to 11" of vertical clearance between the bottom engine bracket and top-tube. The horizontal space between the down-tube and seat-tube should be about 9".
Engine
After finding a suitable bicycle, the next step is selecting a suitable engine. You can adapt almost any small gas engine to a bicycle frame, or you can buy a complete engine kit.
Shop: Bicycle Motor Kit
Bicycle Engine Kits
Aside from the engine, bicycle engine kits generally include a carburetor, ignition coil, fuel tank with fuel valve, and an exhaust pipe that routs away from the rider's leg. Getting power to the rear wheel is taken care of by a chain, chain tensioner, and rear sprocket.
To operate a motorized bicycle, you'll need a throttle and throttle cable, and clutch lever and cable. You will also need a kill switch to shut the motor off. Most engine kits supply these parts as well.
The mounting brackets that are supplied with the engine kits are generic, meaning they have no specific application. Although kits come with hardware (nuts, bolts, washers, spacers, etc.) they may not fit your particular bike.
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Chances are you'll need to do a little problem solving to mount the engine to your bike securely. Be prepared to work out your own solutions for engine placement and mounting.
Confusing Directions
You'll notice that the majority of bad reviews of bicycle motor kits is aimed at the directions. The reason for this is, since nearly every engine kit available is made overseas, the instructions were translated from a foreign language into English. Sometimes they're hard to understand, and sometimes they're just plain wrong.
To add to the confusion, it's common for one manufacturer to copy another manufacturer's instructions, compounding errors and confusion.
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Extended Cranks
Because a four-stroke is wider than a two-stroke, there may be interference with the crank and pedals. Extra-wide crank assemblies are available for some, but not all, popular bicycles.
Rear Mount Motor
Some motor kits supply both chain drive and friction drive. A rear-mounted motor works with the friction drive kit.
Component Upgrades
Exhaust systems, fuel tanks, and kick-stands often get upgraded on motorized bikes. You may also want to upgrade your brakes, or at least make sure they're in top working condition.
Tools And Supplies Needed
To mount bicycle engine kits, only basic hand tools are required, including screwdrivers, wrenches, and a 3/8" drive ratchet with sockets. You will also need a chain breaker to cut the chain the proper length.
Caution: There are safety risks involved with any motorized project. You should be somewhat mechanically inclined to install a gas-powered engine on a bicycle.
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