How to convert a bicycle to a gas motor

Written by scott knickelbine
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How to convert a bicycle to a gas motor
Motorised bicycles can deliver more than 200 miles on a gallon of gas. (a mobylette image by David Monjou from Fotolia.com)

Motorised bicycles are among the most fuel-efficient vehicles. A bike with a small 4-stroke engine can deliver more than 200 miles per gallon and reach speeds of about 35mph. Best of all, you can convert the bicycle you already own into a motor-driven bike--or "moped"--for less than £520. The bike will quickly convert to pedal power when you're on an even grade or going downhill, so you can push your fuel efficiency even more.

Skill level:
Moderate

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Things you need

  • Tape measure
  • Drive Ring
  • Belt
  • Lower mount strap
  • Safety cover
  • Front mount strap
  • Small gas engine (25cc to 40cc) with bicycle mount bracket and drive assembly
  • Trigger throttle with attached cable
  • Engine kill button and wire
  • 4-in-1 key for rings, spokes and gears
  • Nuts, bolts and washers
  • Clutch knob
  • Zip ties

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Instructions

  1. 1

    Measure the distance between your rear bike fork to the spokes of your rear wheel. Most drive wheel attachments require about 1 1/4 inches of clearance from the fork to the spokes, measured about 8 inches from the rear axle mount. If you don't have this clearance, you'll need to select a different bike or contact the motor's manufacturer about ways to modify the installation.

  2. 2

    Remove the rear wheel of the bike and place it sprocket-side down on a work bench.

  3. 3

    Align the drive ring so that the slots in the ring line up with the spokes on the rear wheel.

  4. 4

    Place the 4-in-1 key on the outside of the drive ring, so that a spoke fits into the small slot on the right side of the key. Place a screwdriver through the hole in the top of the key, and use it to lever the key up so that the spoke snaps into the slot on the ring. Repeat this procedure for the spoke on the opposite side of the wheel. Continue the procedure with spokes on alternating sides of the wheel, until all spokes are engaged in drive wheel slots.

  5. 5

    Place the drive belt around the slot in the drive ring and reinstall the wheel on the bike.

  6. 6

    Secure the two mounting straps to the engine bracket with nuts and bolts

  7. 7

    Loosen the nuts on the rear axle and slip the lower mounting strap between the nut and the outside of the rear fork. Be sure that the drive belt is entirely forward of the strap; you may need to remove it from the drive wheel to do this. Secure the axle nut so it is snug, but not tight.

  8. 8

    Install the drive belt on the engine by running it around the gear on engine's driveshaft, between the gear and tension arm bearing. Install belt on drive ring--with tension lever in OFF position, hold belt on left side of drive ring as you guide belt into the belt track of drive ring.

  9. 9

    Reinstall the belt onto the drive ring by holding it on the left side of the ring and guiding the belt into the belt track on the ring. The engine tension lever should be in the OFF position for this procedure.

  10. 10

    Attach the front mounting strap to the rear of the bicycle frame, using the same bolt that attaches either the rear bumper or the rear break calipers to the frame.

  11. 11

    Tighten axle nuts securely.

  12. 12

    Attach safety cover over the tension lever assembly, using the provided wing nut. Make sure the lever has room to move smoothly.

  13. 13

    Mount the throttle trigger to the right front handle bar, just in front of the brake lever.

  14. 14

    Mount the kill button to the left handle bar, so that the button will make contact with the metal of the handlebar when depressed.

  15. 15

    Run the wires for the throttle and the kill button back to the engine, wrapping them loosely along the bike frame and keeping them away from any moving parts. Secure the wires into position with zip ties.

Tips and warnings

  • It's often easiest to buy a mounting kit from the same supplier who sold you the engine. That way, proper fit is their responsibility, not yours.
  • Lubricating the slots in the drive wheel with a little liquid soap will make it easier to snap the spokes into them.
  • As you're levering the spokes into the drive wheel slots, you may want to put a small scrap of cardboard between the tip of the screwdriver and the drive wheel to keep from scratching up the drive wheel.
  • If you have plastic-coated handle bars, you'll need to cut or scrape away a portion of the coating under the kill button, so it can make a good electrical connection to the metal underneath.
  • This describes a typical installation, but the installation requirements may vary with different engines and bikes. Make sure to consult the installation instructions from the manufacturer of your engine and/or mounting kit to assure proper installation.
  • An improperly installed engine can cause injury to you and damage to your bike. Follow all manufacturer's assembly instructions carefully.
  • Be sure all axle and mounting strap nuts are tightly secured before starting the engine.
  • Check your local regulations for licensing and helmet requirements for a motor-driven bicycle.

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