Compression Pressure

NOTES
- A compression pressure test is performed on the engine cylinders to determine the condition of the rings, valves and head gasket.
- Run engine until it reaches normal operating temperature. Battery must be at or near full charge.

1. Disconnect "BAT" terminal connector from distributor.
2. Remove spark plugs from all cylinders.
3. Remove air duct or air cleaner from throttle body and block throttle plate in open position.
4. Measure engine compression.
5. Install compression gage firmly to cylinder spark plug hole.
6. Have a helper crank the engine through at least four compression strokes in the cylinder being tested and check the readings on the gage at each stroke. Record the results.
7. Disconnect gage.
8. Repeat compression test for each cylinder.
9. Inspect recorded compression readings for all cylinders. The lowest reading should not be less than 70% of the highest and no cylinder reading should be less than 689 kPa (100 psi).

Problem areas can be identified as follows:
- Normal - Compression builds up quickly and evenly to specified compression on each cylinder.
- Piston Rings - Compression is low on first stroke and tends to build up on following strokes, but does not reach normal. Compression improves considerably with the addition of oil.
- Valves - Compression is low on first stroke and it does not tend to build up on following strokes. Compression does not improve much with the addition of oil. Use approximately three squirts ( one tablespoon ) from a plunger type oil can.
- Head Gaskets - Leaking head gaskets give nearly the same test restilts as valve problems but may be recognized by engine coolant in the crankcase. Head gasket leakage between two cylinders will give low readings on both cylinders.

10. Remove block from throttle plate.
11. Install air duct or air cleaner to throttle body.
12. Install spark plugs.
13. Connect "BAT" terminal connector to distributor.