SI 1191A - Cylinder Compression

What is the purpose of the differential compression test?

• To measure oil pressure

• To measure cylinder static leak rate

• To check magneto timing

• To balance the propeller

At what piston position should the differential compression test be performed?

• Bottom dead center of the power stroke

• Top dead center of the compression stroke

• Middle of the intake stroke

• Bottom dead center of the exhaust stroke

What is the correct air supply pressure for the test?

• 100 psi

• 60 psi

• 80 psi

• 50 psi

What is the critical orifice size specified for Textron Lycoming engines?

• .020 in. diameter

• .040 in. diameter

• .060 in. diameter

• .080 in. diameter

What does air discharged from the exhaust system during the test indicate?

• Intake valve leakage

• Exhaust valve leakage

• Piston ring leakage

• Normal operation

If all cylinder pressures are equal and above 70 psi, the engine is:

• In need of overhaul

• Operating satisfactorily

• Unsafe to operate

• Losing oil rapidly

What does air discharged from the breather or oil filler tube indicate?

• Exhaust valve leakage

• Intake valve leakage

• Piston and ring leakage

• Head gasket failure

What should be done if cylinder pressure is below 60 psi?

• Nothing, it is normal

• Immediately remove and overhaul the cylinder

• Recheck in 10 hours of operation

• Replace the spark plugs

What precaution must be taken before attaching the compression tester?

• Warm the engine to high temperature

• Check that the fuel tanks are full

• Ensure the air supply regulator is not excessive

• Disconnect the battery

A pressure difference of more than 15 psi between cylinders usually indicates:

• Spark plug fouling

• Magneto timing issue

• A need for further investigation

• A normal condition