Compression Test

Test the compression pressure for each cylinder. Low compression pressure may be the fault of the valves or the pistons. The following conditions should be considered when you check the cylinder compression:

• The engine should be at normal operating temperature.
• The throttle must be wide open.
• All the spark plugs should be removed.
• The battery must be at or near full charge.
  1. Place approximately three squirts of oil from a plunger-type oiler into each spark plug port.
  2. Insert the engine compression gauge into each spark plug port.
  3. Crank test each cylinder with four to five compression strokes using the starter motor.
  4. The lowest reading should not be less than 70% of the highest reading. The compression gauge reading should not be less than 689 kPa (100 psi) for any of the cylinders.
  5. Examine the gauge readings obtained after the four "puffs" per cylinder are obtained from cranking the starter motor. The readings are explained in the following descriptions:
     • Normal Condition - Compression builds up quickly and evenly to the specified compression on each cylinder.
     • Piston Rings Faulty - Compression is low on the first stroke and tends to build up on following strokes, but the compression pressure does not reach normal. The compression pressure improves considerably with the addition of oil into the cylinder.
     • Valves Faulty - Low compression pressure on the first stroke. The compression pressure does not tend to build up on the following strokes. The compression pressure does not improve much with the addition of oil into the cylinder.