2. The engine must be at operating temperature, the battery must be fully charged, and the spark plugs must be removed. In addition, you will need an assistant.
3. Turn off; ignition system by disconnecting the high-tension wire from the distributor cap and grounding it to the engine block. Use a jumper wire to ensure a good connection.
4. Install the compression gauge into the spark plug hole No.1.
5. Have an assistant hold the gas pedal all the way down, then crank the engine with the starter. After one or two revolutions, the compression should increase to its maximum value and stabilize. Record the highest reading.
6. Repeat the test on the remaining cylinders. Make sure that the gas pedal remains fully depressed.
7. All cylinders should have approximately equal pressure of about 11-15 bar. If the compression in any cylinder is less than 10 bar, or the difference between any two cylinders is more than 1.5 bar, this indicates a malfunction. Note that compression in a serviceable engine increases quickly: low compression on the first revolution and its subsequent gradual increase indicates wear of the piston rings. If the compression remains low, the valves or cylinder head gasket are burnt out, or the head is cracked. Carbon deposits formed on the backs of the valve heads can also be the cause of low compression.
8. If the pressure in one of the cylinders is low, pour a teaspoon of clean motor oil into it through the spark plug hole and repeat the test.
9. If the compression increases temporarily after this, the cylinder or piston is worn. No improvement indicates that there may be a leak through burnt valves or a blown head gasket.
10. Low compression in two adjacent cylinders is almost certainly caused by a blown head gasket between them. The presence of coolant in the engine oil will confirm this.
11. If the compression in one cylinder is approximately 20% lower than in the others and the engine idles rough, the camshaft lobe may be worn.
12. If the compression is too high, the combustion chambers are probably covered with carbon deposits. In this case, remove the cylinder head and clean the chambers.
13. When finished, install the spark plugs and connect the ignition system and fuel system.