Compression Test

A cylinder compression test can tell you a lot about the mechanical condition of the engine. No single cylinder should be less than 100psi, nor less than 70% of the highest cylinder.

• • The compression test is normal if the pressure builds up quickly and evenly.

  • If the pressure doesn't build up on the first stroke, doesn't reach normal, and improves greatly w/oil, then take a look at the piston rings.

  • If pressure is low on the first stroke, doesn't build on the following strokes, doesn't improve with oil added and the neighbor cylinders are the same way, suspect the head gasket is leaking.

  • When the pressure is low on the first and following strokes, never reaches normal and doesn't improve much with added oil, suspect a valve problem.

• 1. Batteries fully charged and engine at normal operating temperature

  2. Disconnect positive coil wire plug and fuel injector connector

  3. Remove all spark plugs

  4. Block throttle linkage fully open(I use a brick on the accelerator pedal)

  5. Install compression gauge into first cylinder to be tested https://amzn.to/2Hwwf4t

  6. Using starter, crank the engine for ONLY 4 compression strokes(puffs) and record the reading for ALL cylinders. Remember, more than 4 strokes and your playing with it, and will need to be retested

  7. For any that have low compression, add 15ml of oil to the low cylinder(s) and test/record again