Diagnostic Test
When diagnosing engine noise problems, make sure that noises caused by accessories, such as the A/C Compressor and power takeoff, are not mistaken for engine noises. Remove the accessory drive belts to eliminate noise caused by these units. Noise will also travel to other metal parts not related to the problem.
The use of a stethoscope can help locate an engine noise.
Engine noises heard that are at Crankshaft speed (engine RPM), are noises related to the Crankshaft, Pistons, Connecting Rods, and piston pins. Noises heard that are at Camshaft speed (one-half of the engine RPM), are related to the valve train. A handheld digital tachometer can help to determine if the noise is related to components operating at crankshaft or camshaft speed. Engine noise can sometimes be isolated by performing a cylinder cutout test. If the volume of the noise decreases or the noise disappears, it is related to that particular engine cylinder. There is not a definite rule or test that will positively determine the source of a noise complaint. Engine driven components and accessories, such as gear-driven fan clutches, hydraulic pumps, belt-driven Alternators, A/C Compressors, and Turbochargers can contribute to engine noise. Use the following information as a guide to diagnosing engine noises.