POWER LOSS:

Before a successful tune-up can be performed, it must be determined if the engine is in a satisfactory mechanical condition. An engine that has burned or leaking valves, worn piston rings, sticking valve lifters, leaking cylinder head gaskets or other mechanical malfunctions, will not perform efficiently even after being tuned-up. These conditions must be corrected before an engine can be tuned to perform satisfactorily and efficiently.

Since the power developed by an engine on its power stroke is largely dependent on the efficiency of the compression stroke, and because of the testing convenience afforded, the compression stroke is used for testing engine condition.

During the compression stroke the air-fuel mixture is compressed in the tightly sealed combustion chamber. Should any openings be created by burned valves, leaking gaskets, or worn piston rings, the reduced amount of the air-fuel mixture would proportionately reduce the power output of the engine.

Leakage at any point in the combustion chamber will effect efficient engine operation. Leaking intake valves will allow a portion of the air-fuel mixture to be pushed back into the manifold during the compression stroke and less fuel will be available for the power stroke. During the power stroke, the expanding gases will leak past the burned valves and less pressure will be available on the head of the piston. Also burned gases will be forced into the intake manifold to mix with the air-fuel mixture. A diluted air-fuel mixture will then be available for the next intake stroke and consequently less power will be developed by the engine. If the exhaust valve is burned, the expanding gases will leak through it and less power will be available from the cylinder.

Any leakage past the piston rings will also affect the power of the engine. During the compression stroke, part of the air-fuel mixture will be forced into the crankcase and cause oil contamination. The power stroke will also force burned gases into the crankcase. These gases will overheat some of the oil, turning it to carbon and the oil will become contaminated.

A leaking head gasket will permit water to be drawn into the cylinder during the intake stroke. During the compression and power strokes, gases will be forced from the combustion chamber into the cooling system and cause the engine to overheat. Also, a less dense air-fuel mixture will be available for the power stroke.

It is obvious that conditions of compression stroke leakage are proportionately reflected in engine power loss and must be corrected before an engine can be properly tuned.

POWER LOSS