Which wear test measures the maximum pressure of engine cylinders while cranking?

The compression test is specifically designed to measure the maximum pressure generated within the engine cylinders during the cranking process. This test involves using a compression gauge that is inserted into the spark plug hole of each cylinder. As the engine is cranked, the gauge records the pressure that builds up, indicating the health and performance of the engine's compression system.

This is critical for diagnosing issues like worn piston rings, leaking valves, or head gasket failures. High compression readings suggest that the engine is sealing well, while low readings may point to potential problems that need to be addressed for optimal engine performance.

Other tests mentioned do not serve this specific purpose. For instance, the cylinder leakdown test evaluates how well the cylinder retains pressure by measuring the amount of air that leaks out when pressurized air is applied, but it does not measure maximum pressure during cranking. The Magnehelic test is typically used to measure differential pressure, and the crankcase pressure test focuses on pressures within the crankcase rather than the combustion chamber. Thus, the compression test is uniquely suited for measuring the maximum pressure in engine cylinders upon cranking, confirming its validity as the correct answer.