Piston Pin Noises

Piston Pin Noises Points : piston pin noises, engine noise analysis, problems in internal combustion engines, ic, engine, auto diesel The most common piston pin noise is the result of excessive piston pin clearance. This provides a sharp, metallic, double knock, generally audible with the engine idling. On some engines, however, the noise is more noticeable at car speeds of 25 to 35 mph. interference between the upper end of the connecting rod and the pin boss (bossing) is difficult to diagnose and can be mistaken for a loud valve lifter noise.

To test for piston pin noises, allow the engine to run at idle speed. In most cases, a sharp metallic double knock will be evident when the spark plug in the cylinder with the loose piston pin is shorted out. When the spark plug is shorted, the knock will become more audible. Retarding the spark will generally reduce the intensity of the knock. If the pins in all cylinders are loose, a metallic rattle, which is impossible to short out in any one cylinder, will be heard.