Engine Installation Guide By Tom

Installing a motorized bicycle engine on a Trek mountainbike

  1. Anton
    A short guide to installing a motorized bicycle engine on a Trek mountain bike by Tom.

    This is an overview of the kit that is installed on my Trek mountain bike. Total install time: About 3 hours.

    I bought this kit from eBay; it was close to $150 after tax and shipping. It pretty much included all the parts to get my bike going.

    1. mounting rear drive sprocket motorized bicycle.jpg
    First thing I did was install the sprocket to the left side of the rear wheel. This is not very technical, but a little tedious. This sprocket is fixed to the spokes on the wheel. The difficult part is just taking the time to tighten down all the 9 bolts.

    2. mounting engine on motorized bicycle.jpg
    Once the sprocket was installed, I mounted the engine. It was not hard at all to mount. All you have to do is set it in and bolt it down. A total of 2 mounts and 4 bolts. (See the 2 circles on the picture) It’s a piece of cake if it fits your frame properly. If you have over-sized tubes, it requires a bit of modification.

    3. mounting motorized bicycle carby.jpg
    Next I put the carburetor on. This was as straight-forward as can be. It just slid onto the intake manifold. The big green thing (circled in red) is the air cleaner. There are 2 screws holding that on, again, really easy to install.

    4. mounting motorized bicycle gas tank.jpg
    Then I installed the gas tank. It fits right on the top of the frame. On my first bike, I had a major issue with the gas tank falling over, so this time I made sure to put some pieces of electrical tape between the tank and the frame to increase the friction enough to hold it down tight. It is very solid on there now. Then I connected a tube from the tank straight down to the top of the carburetor to supply fuel.

    5. mounting CDI engnition on motorized bicycle.jpg
    Next I installed the spark plug and the coil. Very easy to mount this little black box to the frame using tape and zip-ties. The thick black wire goes to the spark plug and the other wire connects to the wires coming out of the bottom of the engine (not pictured).

    6.mounting kill switch on motorized bicycle.jpg
    While I was doing wiring, I also installed the kill switch. This was a no-brainer. The button mounts to the frame somewhere (which is an electrical ground) and one wire is routed to the engine. If you press the button, it temporarily cuts the spark and thus stops the engine.

    7. mounting clutch & throttle lever on motorized bicycle.jpg
    My controls are a little different than other bikes. First, I have a goofy horn that I got for my birthday. Also, I have a throttle lever instead of a twist throttle. This is because my twist throttle broke, and I just slapped an extra lever on there to make it work. This item is circled in red in the picture. The other item is the clutch lever. Above each of these are the stock break levers. The throttle hooks up to the carburetor and the clutch hooks up to the engine, described next.

    8. installing clutch cable on motorized bicycle.jpg
    Adjusting the clutch can be a little tricky your first time. Basically the clutch handle just pulls the lever circled in the picture, and thus releases the clutch. If you release the handle, the lever swings back and the clutch is engaged.

    9. mounting chain tensioner on motorized bicycle.jpg
    Finally I routed the chain. The toughest part by far is getting the chain to align correctly with the right tension. There is a chain tensioner that most bikes need, to pick up the extra slack in the chain. Keep in mind that you will need a chain breaking tool to put the chain on.

    After all that, I fired up my bike and it worked fine! I was surprised that it fired up the first try. I added a light that is powered off the electricity generated by the motor, so I could ride safely at night.

    Once in a while you need to tighten various bolts since they vibrate so much while driving.

    If you have any questions, just post on the forum and your questions should be answered!