How to Build Your Own Small Engine

by Tom Fritchman

Building your own small engine is a good way to provide a back up power source for your home or remote camp site, but you need to build it properly. A proper engine can convert the power of a motor, which runs on gas, into the electrical power needed to recharge batteries and operate other electronics. Follow these steps to build your own small engine.

Cut one piece of plywood to 2 feet by 2 feet. Cut two pieces of your 2x4 lumber to 4 feet. Cut two pieces of your 2x4 lumber to 1 foot 10 and 1/2 inches.

Build a box 2 feet by 4 feet by screwing your 2x4 lumber along the perimeter of your piece of plywood.

Place your lawnmower motor on your box so that the mounting holes touch the plywood. Use your pencil to mark these holes, then remove the motor. Drill holes with your power drill into the center of each of the four marks you made.

Put the lawnmower motor over the holes you drilled so that they line up with the mounting holes on your motor. Slide bolts through each hole. Fasten each bolt into place with your washers and nuts.

Place your alternator on the plywood. Put the drive belt around the wheel sections of both your motor and alternator. Slide the alternator farther away from the motor until the drive belt becomes taut. At this point, mark the location of the four mounting holes for your alternator.

Remove the drive belt. Remove the alternator from your plywood. Drill each of the four holes you marked.

Place the alternator back on the plywood. Verify that the mounting holes line up with the holes you drilled. Secure the alternator to the plywood using your bolts, washers, and nuts.

Items you will need

  • Lawnmower motor
  • Car alternator
  • Plywood
  • 2x4 lumber
  • Power drill
  • Screws
  • Bolts
  • Nuts
  • Washers
  • Lawnmower drive belt
  • Lawnmower gas


  • Try obtaining an alternator from a used parts supplier rather than removing one from an existing vehicle. This can cause irreparable harm to the vehicle.


  • Wear safety goggles when operating power tools.
  • Removing the motor from an existing lawnmower will invalidate the warranty.

About the Author

Tom Fritchman is a freelancer who has been writing professionally since 2009. His first writing credit was actually a stage play called "Window Watching" performed at the Northmont Auditorium in Clayton, Ohio. He holds a Bachelor of Arts in language and literature from Wright State University.