Compression Check: Testing and Inspection

COMPRESSION CHECK
- Disconnect the primary terminal from the ignition coil.
- Remove all spark plugs.
- Block the throttle plate wide open.
- Make sure the battery is fully charged.
- Starting with the compression gauge at zero, crank the engine through four compression strokes (four "puffs").
- Make the compression check at each cylinder and record each reading.
- If some cylinders have low compression, inject 15 ml (one table spoon, or 3 squirts from a pump type oil can) of engine oil into the combustion chamber through the spark plug hole.
- See Specifications for minimum pressure and maximum variation. Specifications

Normal Compression: Compression builds up quickly and evenly to specified compression on each cylinder.

Piston Rings Leaking: Compression low on first stroke, tends to build up on following strokes, but does not reach normal. Improves considerably with addition of oil.

Valves Leaking: Low on first stroke. Does not tend to build up on following strokes. Does not improve much with addition of oil.

Head Gasket Leakage: If two adjacent cylinder have lower than normal compression, and injecting oil into cylinders does not increase the compression, the cause may be a head gasket leak between the cylinders.