NOISES
The noises made by the engine when operating properly become so familiar to the careful automobilist that any other sound is recognized more by instinct than by attention. Faults will often make themselves known by noises, and these may be broadly classified as pounds or knocks, hisses, squeaks, and rattles. A pound that occurs regularly may be due to a loose connecting rod or wrist-pin bearing, and in this case will be heard once to every two revolutions of the crank shaft. A pound that occurs oftener than this may be set down as a loose crank-shaft bearing, or a loose or cracked fly wheel. If often happens that a fly wheel in this condition will make itself heard, while sufficiently tight to show no sign of the defect on casual inspection.
A hard metallic pound is caused by the combustion of the charge before the completion of the compression stroke; this condition may result from preignition or from the spark being too far advanced. If the latter is the case, retarding the spark will stop the pounding.
Hisses are due to leaks in the combustion space, as already described.
Squeaks indicate a dry bearing, or a lack of lubrication in one of the moving parts. The bearing may be detected by its heat. A squeak of the leaves of a spring will often be difficult to trace and locate, because of its irregularity.
Rattles indicate that something is loose, and should be located without loss of time. All nuts and bolts should not only be tight, but in addition secured in position by the use of lock nuts or cotter pins.
Backfiring, which is an explosion of the mixture in the inlet pipe or carburetor, may be due to a stuck inlet valve that permits flame to pass and ignite the mixture before it reaches the combustion space, but more probably either to ignition occurring so late that combustion is still occurring when the inlet valve opens, or to preignition.
Explosions in the exhaust pipe or muffler are due to the presence of unburned mixture, which is passed out of the exhaust valve after ignition has failed, and ignited by the heat of the exhaust pipe, or by the hot gases from the next explosion.
CHAPTER XIII
MAINTENANCE AND CONSTRUCTION
In order that an automobile may be maintained at its highest efficiency, a constant watch must be kept over all of its parts, and repairs and replacements made as soon as the necessity is apparent. A worn bearing or loose part may continue to operate, but the wear will be far greater than would occur under normal conditions, and may result in serious breakage. A system of inspection to be gone through every time that the car is used will keep the driver informed as to its condition, and it is best to form the habit of doing this at the end of a run rather than before, for then the necessity for making readjustments or repairs will be fresh on the mind.