Mechanic’s Stethoscope

A metal probe touches the part being checked. It helps find bearing noise or injector ticking. Electronic versions use clamps on several points. Noise travels through metal, so a sound heard loudly at one point is usually close to its source. A long screwdriver held to the ear is a traditional alternative but is less clear. Comparing the sound of the same part on both sides of the engine, such as injectors, helps identify the faulty one.

The probe carries vibrations to the earpieces.

Keep away from moving belts and fans. Compare similar parts to judge noise.