Piston rings are usually prevented from revolving around the piston by pins driven into the piston between their ends; if these are not provided, the turning of the rings will bring their ends into line, and the pressure will leak through them. The appearance of the rings is the best indication as to whether they are permitting leakage; if they are tight, they will be smooth and polished all around, but if there is leakage, they will be streaked with black carbon deposit.
Other losses of compression may be due to a cracked piston, cylinder head or wall, the former being indicated by a hot crank case and the latter by the presence of water in the cylinder and crank case.
COOLING TROUBLES
The failing of the cooling or lubrication systems will permit the engine to heat, and if continued will produce disastrous results. The radiator of a water-cooled engine should begin to heat shortly after the engine has started, and will rapidly become warm all over, thus showing that the water is circulating properly. A failure of the circulation may be due to a clogged pump or passage, and the cause should be located and removed without delay. Dirt in the water is the most usual cause of the failure of the pump, and also of the stopping of the circulation in the gravity system. A strainer should be fitted to the filling cap of the radiator to remove bits of wood, leaves, sand, etc. The connections of the water system are frequently made of rubber hose, and this in rotting will free bits of rubber that will prevent the flow. A difficulty occurring at the clamps that attach the hose to the metal pipes is the tearing off of a strip of the rubber lining, which closes the passage after the manner of a valve.
The fan must be kept running correctly, and if belt-driven, the belt must be kept tight and the pulleys free from oil that would permit slipping.
Water that has been heated freezes much more readily than water that has not, and therefore the water system of an automobile must be carefully guarded against low temperatures. A freeze of the water may crack the water jackets or split the radiator, either of which will require the laying up of the car for repairs. The best protection is to draw off the water if there is the slightest danger of freezing, drain cocks being provided at the low points of the system for this purpose. If this is not practicable, a solution of four pounds of calcium chloride to the gallon of water, mixed hot and allowed to cool, may be used, and it will stand a temperature of 15° F. below zero without freezing.
The flanges or corresponding parts of an air-cooled motor should be kept clean, for dirt will prevent the free radiation of heat.
A lack of lubricating oil, either through the failure of the supply or the clogging of the pipes, will cause the engine to heat and the piston to stick or seize. When the car is new, it is better to supply too much oil than too little, but when the bearings have smoothed down the supply may be reduced. The operation of the engine is the only indication as to whether it is receiving a proper amount of oil, and rather than run the risk of underlubricating the piston rings and cylinder walls, it is better to have enough to produce a faint smoke at the exhaust pipe. This will show that the engine is receiving a little more than is necessary. Too much oil in the cylinder will foul the spark plug, and as this would prevent the passing of the spark, it is to be as much avoided as too little.
When the lubricator pipes are clogged, the easiest method of clearing out the obstruction is to force air through them by means of a foot pump.