Crank Mechanism Troubles

The normal operation of the crank mechanism is governed by the condition of its component parts. In service, the normal operation of the tractor or automobile may be disturbed as a result of some troubles. The most common among these are worn rubbing components, drop of compression in the cylinders, and oil and water leaks. Worn components are indicated by foreign engine noises (knocks), excessive oil consumption, smoky exhaust, and loss of engine power.

To locate the source of a noise due to excessively worn components, it is necessary to adjust the engine speed with the fuel pump or throttle lever so as to make the knocks most audible. It is recommended that the engine should be listened to with the aid of a mechanic's stethoscope or listening rod to carry the sound directly to the ear. To do this, the pickup end of the stethoscope or rod is moved around on various places on the engine to find where the noise is loudest. Engine noises vary in intensity and frequency, depending on their source. Thus, a sharp, metallic knock growing in intensity with increasing engine speed results from worn piston pins or their bushings. Dull, heavy metallic knocks audible in the lower part of the cylinder-block-and-crankcase unit, which vary in fre­quency as the engine speed is sharply chang­ed, especially under load, are indicative of worn connecting rod or main bearings. A decrease in the oil pressure in the lubricating system is an additional indication of worn main bearings. Worn pistons or cylinder liners give rise to a clicking sound audible in the cylinder block at the beginning of the engine warm-up period after starting.

Indications of worn piston rings are poor engine performance due to decreased compression in the cylinders and excessive crankcase oil consumption as a result of increased pumping action of the compression rings pumping oil into the combustion chamber.

A bluish tinge of the exhaust gas indicates that the engine is burning oil entering the combustion chambers because of worn cylinder liners, worn pistons, or worn or else stuck piston rings. Whitish exhaust smoke indicates water in the cylinders. The leakage of water into the cylinders from the water jacket can be eliminated by tightening up the nuts on the cylinder head studs. This is done with a torque indicating wrench in two or three operations in a definite sequence, working evenly from the center out to the extreme nuts at both ends of the head in a criss-cross fashion.

Bad condition of the rubber sealing rings between the cylinder liners and cylinder-block-and-crankcase unit may result in the jacket water leaking into the oil pan. The leakage of oil from the oil pan, bell housing, and timing case may be due to damaged or poorly fitting gaskets or, in some cases, worn crankshaft front and rear seals.

If an oil leak is detected, one should tighten up all the fasteners and, should this fail to rectify the situation, replace the damaged gaskets or worn sealing components. To avoid the ingress of dust into the engine interior, worn components are replaced at a shop, where the engine prior to disassembly is checked by an engine diagnostician, i.e., a diagnostic technician, on a test stand.