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Compression test engine

Compression test engine


1. Charge the battery if it is not fully charged.

2. Disconnect the ignition system.

3. Disconnect the fuel injection system.

4. Remove the spark plugs.

5. Turn the ignition to the ON position.

6. Depress the accelerator pedal so that the throttle valve is fully open.

7. Start with the compression gauge reset and turn the engine over by means of 4 compression strokes, four "nudges".

8. Measure the compression in each cylinder. Note the values.

9. If a cylinder has low compression, inject about 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole. Measure the compression again and note the value.

10. The lowest compression in any cylinder must not be less than 70 percent of the maximum cylinder. No cylinder may be lower than 690 kPa (100 psi). For example, if the maximum pressure in a cylinder is 1035 kPA (150 psi) the minimum permissible pressure in any cylinder is 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).

• Normal - the compression is built up quickly and evenly to each cylinder to the specified level.

• Leaking piston rings - the compression is low during the first stroke. The compression is built up during the following strokes, but does not reach normal value. The compression is increased significantly when you add oil.

• Leaking valves - the compression is low during the first stroke. The compression does not normally increase during the following strokes. The compression does not improve much when you add oil.

• If two adjacent cylinders have lower compression than normal, and injecting oil into the cylinders does not help, then the cause may be that the cylinder head gasket is leaking between the cylinders.