Connecting rod troubles usually involve either the connecting rod bearing or the piston pin bearing. Some of these troubles, such as misalignment, defective bolts, cracks, or plugged oil passages, can be avoided by performing proper maintenance and by following instructions in the manufacturers technical manual.

Misalignment causes binding of the piston, piston pin, and the connecting rod journal bearing.

This binding is likely to result in breakage and in increased wear of the parts, leading to total failure and possible damage to the entire engine structure. Connecting rods must be checked for proper alignment before being installed in an engine, and after any derangement involving the piston, cylinder, or crankshaft. Defective bolts are often the result of over-tightening.

Connecting rod bolts should be tightened by using a torque wrench, or an elongated gage to ensure that a predetermined turning force is applied to the nut. Defective threads can cause considerable trouble by allow-ing the connecting rod to be loosened and cause serious damage to the engine. Whenever rod bolts are removed they should be carefully inspected for stripped or damaged threads and elongation.

Cracked rods are usually the result of overstressing caused by overloading or overspeeding or because defective material was used at the time of manufacture. It is of prime importance to discover the cracks before they have developed to the point where the failure of the rod will take place. No attempts should be made to repair cracked rods. They should be replaced; serious damage may result if breakage occurs during operation.

Restricted oil passages are often the result of improper assembly of the bushing and the con-necting rod bearing inserts. They may also be due to foreign matter lodging in the oil passages.