How to Build a Gas Powered Air Compressor


A gasoline powered air compressor is a great tool to have if your need is for a portable air compressor. By shopping carefully, one can build an air compressor which will be powerful enough to operate air tools and will be portable enough to do it anywhere.

Things You'll Need

  • Compressor head Gas engine 3.5 inch pulley to fit engine shaft with belt groove to match compressor pulley Drive belt Unloader valve Check valve Throttle control Air tank Pressure gauge with 3/8 inch pipe thread 3/8" Brass pipe tee ¼ inch tubing 3/8" x 1' Airline hose 3/8" Male fittings for hose Hose clamps Miscellaneous pipe fittings Teflon pipe thread tape ½ " x 1 1/2" Bolts, 14 threads per inch 3/8" x 1 1/2" Bolts, 16 threads per inch 2" x 48" iece of 16 gauge Sheet metal 3' x 3' section of Hardware cloth with 3/8" openings Electric drill 7/16" Drill bit Rotary tool Grinding stones Wrenches Small socket set Pop rivet tool 3/16" x 1/4" Pop rivets
  • Buy an air tank with a mounting plate on the top of the tank. An example of this would be found in the first link in the Resources section below and comes from Granger Industrial Supply. Measure the holes for the air input and safety valve, as you will need this information later in the build.

  • Bolt the compressor to the mounting plate using 1/2 " 14 tpi bolts and nuts about 1.5 inches long.

  • Purchase a horizontal shaft gasoline engine of at least 5 horsepower rating. It must not be a gear reduction motor. A good one for this project is found in the second link below.

  • Set the gasoline engine on the mounting plate. Carefully align the drive pulleys and measure the distance around the outside of them where the drive belt will be. With this measurement in hand you are now able to purchase and temporarily install the drive belt.

  • Mark the location of the engine mounting holes on the mounting plate and remove the engine.

  • Using a center punch, make a punch mark at the center of each engine mounting hole location. Make another punch mark ¾" fore and aft of these marks. Then, drill all 3 holes at each location using a 7/16" drill bit.

  • Use a rotary tool and join the three holes to form a slot. Do this at each engine mounting bolt location.

  • Place the engine back on the mounting plate and install a 3/8" by 16 TPI by 1.5" bolt at each mounting hole. Do not tighten too much just yet.

  • Install the drive belt on the engine pulley and compressor pulley.

  • Slide the engine back in the slots on the mounting plate until the belt is tight. You should be able to push the center of the belt down about ½" when the tension is correct. Tighten the engine bolts securely.

  • Make a belt safety guard by forming the 2" x 48" 16 gauge sheet metal around the pulleys and belt, allowing at least ½" clearance between the guard and belt. Cut to the proper length after forming and join the ends with two 3/16" pop rivets. Form brackets from the same sheet metal and attach to the engine and compressor. Close the front of the guard with the hardware cloth, pop riveted to the sheet metal guard.

  • Install the unloader valve (see the third link below as an example) in the airline threads on the compressor.

  • Mount the throttle control valve (the fourth link below leads to one) on the engine. The exact mounting will vary by engine model, but generally the throttle control valve will mount on the throttle plate of the engine and connect to the throttle linkage with a rod or cable.

  • Connect the throttle control valve to the unloader valve with ¼" nylon airline tubing and compression fittings. Clamp the air line tubing to the engine using cable clamps to secure it and help support the throttle control.

  • Screw the check valve into the air in-port on the tank. The correct size for the valve will be the measurement of the air in-port of your air tank, minus 1/4".

  • Install a brass pipe tee to the check valve.The tee will be the same thread size as the check valve, which will be either 1/4" or 3/8". Mount the tee to the check valve with one opening to the side.

  • Install the air pressure gauge in the side opening of the brass tee.

  • Install the male air hose fittings in the one-foot-long piece of 3/8" air hose and secure with hose clamps.

  • Connect the brass tee to the unloader valve using the one-foot-long piece of 3/8" air hose..

  • Install the safety release valve in the tank. It will screw in to the port.

  • Check the oil levels in the engine and compressor.

  • Start the engine and check for proper operation of the throttle.

  • Check for air leaks.

Tips & Warnings

  • Wrap all male threads with teflon pipe thread tape before assembly to help prevent air leaks. To determine correct size of all pipe threads, measure the threaded hole where the pipe threaded piece will install and subtract ¼". For example, a threaded hole measuring ½" would be for a ¼" male pipe thread.
  • Wear safety glasses when drilling and grinding. Safety guard must be installed.

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