Compression Test Method

[pbanders]

From the Clymer's guide on the 914 (I made some slight adjustments to the pressures for ease of interpretation):

1. Dry test only. Wet test (pouring a teaspoon of oil into the cylinder through the open spark plug hole) doesn't work right on horizontally-opposed engines because there is uneven wetting of the cylinder wall.
2. Warm engine completely before the test.
3. Remove all plugs, disconnect power supply lead to the coil.
4. Connect compression tester to cylinder 1.
5. Have assistant crank the car with the throttle held wide open.
6. Crank until there is no further rise in pressure, record reading.
7. Repeat on cylinders 2, 3, and 4.

Ranges:

• 130 to 160 psig - Good Compression
• 100 to 130 psig - Marginal Compression, worn engine
• Less than 100 psig - Rebuild time

Cylinder-to-cylinder variation should not exceed 20 psig. Larger variations indicate a cylinder(s) with a ring or valve problem. Use a vacuum gauge to diagnose further.

I wasn't smart enough to have kept a record of my engine's compression over the years. Next rebuild, I'm going to keep a careful record of the compression each year.