"Diagnosing" may be defined as a systematic means of identifying a problem by using all available information and facts. Usually, the Equipment Operator will be able to tell the symptoms, such as the engine lacks power, uses excessive oil, has low oil pressure, or makes certain noises.
Some internal engine problems may be found by listening for unusual noises and knocks or by examining the exhaust gases for indications of incomplete combustion. Then too, placing an artificial load on an engine can emphasize certain noises; for example, applying the brakes and partially engaging the clutch with the vehicle transmission in high gear. In this manner, the engine operating under a load can be heard without the interference of body noises.
There are also other tricks of the trade that a mechanic may use, such as feeling the oil or shorting out the spark plugs to get an idea of the source of trouble.
Excessive oil consumption would probably first be noted by the Equipment Operator who has to add oil to maintain the proper oil level. There are two main causes of excessive oil consumption: external leakage and burning in the combustion chamber.
External oil leaks can often be detected by inspecting the seals around the oil pan, valve covers, timing gear housing, and at the oil line and oil filter connections.
The burning of oil in the combustion chamber usually produces a bluish tinge in the exhaust gas. Oil may enter the combustion chamber in two ways: (a) through clearances caused by wear between the intake valve guides and stems and (b) around the piston rings.
Excessive oil consumption caused by worn valve guides or stems may be indicated by too much carbon on the undersides of the intake valve. In this case, it is usually necessary to install valve seals, new valve guides, or new valves. If excessive oil consumption is caused by worn rings or worn cylinder walls, the supervisor may have the mechanics do a complete engine overhaul.
Low oil pressure often indicates worn engine bearings. Worn bearings can pass so much oil that the oil pump cannot maintain oil pressure. Other causes of low oil pressure include a weak relief- valve spring, a worn oil pump, a broken or cracked oil line, or a clogged oil line. Oil dilution, foaming, sludge, insufficient oil, incorrect oil, or oil made too thin by the engine overheating will also cause low oil pressure.
A variety of engine noises may occur, Although some noises have little significance, others can indicate serious engine trouble that will require prompt attention to prevent major damage to the engine.
A listening rod can be of help in locating the source of a noise. The rod acts somewhat like the stethoscope a doctor uses to listen to a patient's heartbeat or breathing. When one end is placed at the ear and the other end at some particular part of the engine, noises from that part of the engine will be carried along the rod to your ear. By determining the approximate source of the noise, you can, for example, locate a broken or noisy ring in a particular cylinder or a main bearing knock.
Valve and tappet noise is a regular clicking sound that increases in intensity as the engine speed increases. The cause is usually excessive valve clearance. A feeler gauge inserted between the valve stem and lifter or rocker arm will reduce the clearance, and the noise should decrease. If the noise does not decrease when the feeler gauge is inserted, it is probably caused by weak lifter springs, worn lifter faces, lifters loose in the block, a rough adjustment-screw face, a rough cam lobe, or possibly the noise is not from the valves at all.
A noisy hydraulic valve lifter maybe sticking because of dirt in the ball or disk valve. When this happens, you must disassemble the lifter and clean all the parts in a clean solvent. Then reassemble the lifter and fill it with clean, light engine oil.
Connecting rod noise usually tends to give off a light knocking or pounding sound. The sound is more noticeable when the engine is "floating" (not accelerating or decelerating) or as the throttle is eased off with the vehicle running at medium speed. To locate a noise in the connecting rod,Continue Reading