Compression Test: Notes

• 1.
  
  Make sure the oil in the crankcase is of the correct viscosity and at the correct level and that the battery is correctly charged. Operate the vehicle until the engine is at normal operating temperature. Turn the ignition switch to the OFF position, then remove all the spark plugs.

• 2.
  
  Set the throttle plates in the wide-open position.

• 3.
  
  Install a compression gauge in the No. 1 cylinder.

• 4.
  
  Install an auxiliary starter switch in the starting circuit. With the ignition switch in the OFF position, and using the auxiliary starter switch, crank the engine a minimum of 5 compression strokes and record the highest reading. Note the approximate number of compression strokes necessary to obtain the highest reading.

• 5.
  
  Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes.

Compression Test - Test Results 

The indicated compression pressures are considered within specification if the lowest reading cylinder is at least 75% of the highest reading. Refer to the Compression Pressure Limit Chart below.