Testing Compression
CAUTION:
Use a remote starter to crank engine during compression test, NOT the ignition switch. The fuel injectors on many fuel injected models are triggered during the cranking mode. This could cause a fire hazard, flooding, crankcase contamination, hydrostatic lock-up, or lubrication to be washed off of cylinder walls.
- Disconnect the "BAT" terminal from the HEI distributor or ignition module. Check compression pressure with engine at normal operating temperature, all spark plugs removed and throttle valve wide open.
- Insert a recording type compression gauge and crank each cylinder through 4 or 5 compression strokes. The lowest reading should not be less than 100 psi (7.03 Kg/cm2 ). If compression builds up quickly and evenly to specified range on each cylinder, compression is normal.
- Faulty piston rings are indicated if compression is low on the first stroke and tends to build up on following strokes, but does not reach normal specifications.
- Faulty valves are indicated if compression is low on the first stroke and does not build up on following strokes.
- Place 3 squirts of oil from a plunger type oiler into each cylinder. Crank each cylinder through another 4 or 5 compression strokes. Examine gauge readings obtained from each cylinder.
- Faulty piston rings are indicated if compression improved with addition of oil. Faulty valves are indicated if compression is low on the first stroke and does not build up on following strokes or improve with the addition of oil.