Building a motorized bicycle
Back in the summer of 2008, I decided to put together a motorized bicycle. Of course gas prices in and around the 4$ per gallon range influenced me to look into this. After a bit of studying on this, and looking around to see what was available, this is what I struck upon. Realistically, and not counting my labor, I have about 275$ dollars into this, but you could get by much cheaper if you already have an existing bike to use.
I chose to buy and off the rack Walmart Bike for 99$. Pictured to the right is the bicycle just after I got it home. It's model type was a Kulana Moondog. The orange and black theme along with the Cruiser style wide handlebars and big street tires would blend with the engine kit I had decided upon. This kit was a black engine with black teardrop gas tank I purchased off e-bay for 148$. The engine is a 50CC 2 Cycle gasoline. A 2 cycle engines will require oil to be mixed with your fuel.
The engine kit was produced in China and of acceptable quality for my expectations, which were not extremely high. When buying an engine of this type you will need to be at least somewhat handy with a few tools to install it , as it probably will require some tinkering around with to get it to fit correctly. Using hindsight upon this build, the job would be easier if you went for the simplest bike frame possible. A bike frame with small and straight diameter tubes of about 1.5 in. would be the best choice.
Your first major task is to mount the drive sprocket to the rear wheel. Remove the rear wheel to begin. On the left hand side of the wheel mount your drive sprocket to the outside of the spokes centered on the hub. The drive sprocket is held to the spokes using a segmented ring and bolts that mount on the inside of the spoke ring. Be as precise as you can be on centering this drive sprocket, then remount your rear wheel, just as you disassembled it earlier.
Next mount the engine to the frame as per its included instructions. Since the frame of my bike was bigger than the included mounting bracket, I modified the mounting using a 2 inch muffler clamp. mount it tightly to the frame and in the same plane as the drive sprocket on your rear wheel. This will lessen the stress on your drive chain by getting this alignment as close as possible.
With the engine in place you can mount the gas tank to the bicycle top tube, being careful it is positioned to not interfere with your steering or your ability to pedal. I purchased some rubber fuel line and a inline lawnmower gas filter at the local AutoZone, to replace the clear rubber tubing that came with the kit.
Modification using 2" muffler clamp
Left hand clutch lever and right handle bar throttle installed
Drive Chain installed and rear fender nibbled out for clearance
Short clip of engine at idle
Kulana Moondog with 50 cc engine kit assembled
Short clip of engine at idle
Conclusion Motorized Bicycle Build
Mount your throttle assembly on the right hand side of the handle bar and your clutch lever on the left hand side of the bar. Secure each associated cable to your bike and route them to your engine and connect them as per the manufactures instructions.
Mount your drive chain to your engine drive sprocket and to your rear drive sprocket. After you have installed your chain, bolt the chain tensioner that comes with your kit to the bottom tube and adjust so you have one to two inches of slack in your chain. I had to nibble out some metal of the rear fender of this bike to accommodate the drive chain path.
Be sure to mix your gasoline with 2 cycle engine oil. I used about a 40:1 ratio of gas to oil.
Double check all your connections and fittings to make sure they look right and won't come loose. With the tank fueled open the fuel line valve to allow the gas to get to the engine. On your first starting attempt you will need to let the gas have some time to get to the engine. If you installed a clear filter like I did you will see the flow if it is working.
You start the bike by either pedaling or coasting to get some speed and momentum going while having the clutch engaged. When you get to 5-10 mph dis-engage the clutch to start the engine. I recommend after starting the first time to immediately engage the clutch again, park the bike with the engine running and examine everything again closely. Check your throttle, your ignition kill switch. When you feel comfortable that everything is as it should be venture off in an area with little or no traffic to get accustomed to starting, stopping and maneuvering.
You will need several test runs more than likely to get everything adjusted as you like it. The most important thing to get right early on is the correct drive chain tension and alignment. Nothing is more frustrating than the chain coming off track or broken.
Once I had the bugs out of mine, I could get a top speed of about 27 mph and was able to climb normal rolling hills without pedal assist. On the very steep hills pedaling to assist the engine was required, but did not require a huge amount of effort. I am really unsure of the mileage of this little engine but I would imagine you would get well over 100mpg easily.
So do your homework, find a bike you want to try this on, and shop around the internet looking for an engine. 50 and 70 cc engines of this type are easily found and purchased via ebay. You probably won't use this all the time but you will have fun puttering around on it. Wear a helmet and stay safe