What does a compression gauge evaluate in small engines?

A compression gauge measures the pressure created in the combustion chamber of an engine when the piston is at the top of its stroke. This pressure is crucial for evaluating the effectiveness of the piston rings, which are responsible for sealing the combustion chamber to ensure that the fuel-air mixture can ignite and combust efficiently.

When the piston rings are in good condition, they create an adequate seal, leading to higher compression readings. Low compression readings can indicate worn or damaged piston rings, which can affect engine performance, fuel efficiency, and overall operation. Therefore, the compression gauge is a valuable tool for diagnosing the condition of the piston rings and assessing the engine's ability to maintain proper compression during operation.

The other options, while relevant to engine operation in various contexts, do not pertain directly to the primary function of a compression gauge.