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Normal Compression for a Small Two-Cycle Motor

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At its inception in 1897, the two-cycle motor was unable to produce the same amount of power as its counterpart the four-cycle engine. As technology has evolved, so has the performance of two-cycle engines. To determine the compression of a two-cycle engine, take into account the application: The more power required to run a particular tool, the greater the compression.

Lawnmowers

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Because lawnmowers do not require as much power as larger machines, such as automobiles and motorcycles, two-cycle engines suit them. According to Samuel M. Goldwasser's "Compression Testing," normal compression for a lawnmower falls between 60 and 80 lb. per square inch, or psi. A number below 60 indicates a leak or inability of the piston to compress enough air.

  • Because lawnmowers do not require as much power as larger machines, such as automobiles and motorcycles, two-cycle engines suit them.
  • According to Samuel M. Goldwasser's "Compression Testing," normal compression for a lawnmower falls between 60 and 80 lb.

Weed Trimmers

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Weed trimmers, like lawnmowers, require fewer pounds per square inch to operate than do heavier machines so they fall into the 60 to 80 psi range. If a weed trimmer has at least 60 lb. of pressure, the engine will still start, but anything less will not create enough power to turn the engine over.

Boats

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Two-cycle boat engines differ from both lawnmower and weed trimmer engines because they require more pressure to create more power. Boat owners who choose two-cycle over four-cycle do so because of the two-cycle weighs less; many owners opt to purchase two engines instead of one for more power. While four-cycle boat engines often require between 170 and 200 psi, two-cycle engines require only 80 to 140 psi. Compression figures above or below this range signal a malfunction.

  • Two-cycle boat engines differ from both lawnmower and weed trimmer engines because they require more pressure to create more power.

Compression Testers

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Regular compression testing can help ensure that the pressure levels in any small two-cycle engine are up to appropriate standards. Check the compression by pulling out the spark plug, placing the tester in the spark plug port and pull the cord a few times to build up air in the engine. Maintaining optimum compression can extend the life of any two-cycle engine.

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