Practical Hand Book of Gas, Oil and Steam Engines / Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

by John B. Rathbun

(125) Oiling the Magneto.

Never oil the circuit breaker or circuit breaker mechanism, unless for a drop of sperm oil that may be applied to the cam roller by means of a toothpick. If oil gets on the circuit breaker contact points, it will cause them to spark badly, resulting in pitting or destruction of the points. If the oil is occasionally applied to the cam roller or should oil accumulate on breaker points, the breaker should be rinsed out with gasoline to remove the surplus.

Pitted or carbonized contact points are capable of causing much trouble, and gummy oil or dirt will develop this trouble quicker than any other cause. Use only the best grade of thin sperm oil on the ball bearings.

In the course of time the circuit breaker contact points will wear or burn, causing imperfect contact, and too great a separation between the points. The contacts should be examined from time to time, and if rough or pitted, should be dressed down to a flat even bearing by means of a dead smooth file, and the distance readjusted. The contacts should not bear on a corner or edge, but should bear evenly over their entire surface to insure a maximum primary current and spark.

CHAPTER XI
COOLING SYSTEMS

The object of the cooling system is not to keep the cylinder cold, but to prevent the heat of the successive explosions from heating the cylinder walls to a degree that would vaporize the lubricating oil and prevent satisfactory lubrication of the cylinder and piston. The hotter the cylinder can be kept without interfering with the lubricating oil, the higher will be the efficiency of the engine and the greater the output of power.

To obtain the greatest power from an engine, the heat developed by the combustion should be confined to the gas in order that the pressure and expansion be at a maximum, it is evident that the pressure and power will be reduced by over-cooling as the heat of the expanding gas will be taken from the cylinder and transferred to the cooling medium. The temperature of the cylinder, and therefore the efficiency of the engine is determined principally by the vaporizing point of the lubricating oil, and consequently the higher the grade of the oil, the higher the allowable temperature of the cylinder.

If cold water from a hydrant or well be forced around the water jacket rapidly, the power will be greatly reduced owing to the chilling effect on the expanding gas. There is not much danger in keeping the cylinder of an air cooled engine too cool, in fact the great difficulty with this type of engine is to keep it cool enough to prevent an excessive loss of lubricating oil.

The valves, particularly the exhaust valves, should be surrounded with sufficient water to keep them cool as they are subjected to more heat than any other part of the engine, and are liable to wrap or pit. The water leaving the jacket of a gasoline engine should not exceed 160° F., as temperatures in excess of this amount cause deposits of lime scale.

When possible, a portion of the cooling water should be run into the exhaust pipe immediately after it has completed its flow around the valves and cylinders, as the water cools the gas so suddenly that the exhaust to atmosphere is rendered almost noiseless, and the exhaust pipe is kept much cooler and less liable to cause fire by coming into contact with combustible objects.

On some engines the exhaust pipe is water jacketed for some distance to prevent dirty rusty pipes in the vicinity of the engine mechanism and also to prevent injury to the operator should he come into contact with the pipe.

Small engines and medium size vertical engines usually have the water jacket cast in one piece with the cylinder casting and others have a separate head that is bolted to the cylinder.

In the latter type the water flows from the cylinder to the head through ports or slots cut in the end of the cylinder water jacket that register with similar slots in the jacket of the head.

Thus in this construction we have not only to pack the joint to prevent leakage of gas from the cylinder, but also to prevent the leakage of cooling water from the jacket into the cylinder, or outside. Thus there is always a chance of water leaking into the cylinder bore and causing trouble unless the packing is very carefully installed and looked after.

In large horizontal engines the gas and water joints are never made at the same point, as it would be practically impossible to prevent leakage into the cylinders of such engines.

When the cylinder and cylinder water jackets are cast in one piece without a water joint at the junction of the cylinder and the head, the water connection between the head and the cylinder being made by pipes external to the castings.

Small, portable, stationary engines are sometimes “HOPPER COOLED,” or cooled by means of the evaporation of the water contained in an open water jacket that surrounds the cylinder.

The hopper is merely an extension of the water jacket such as used on all water cooled engines, the only difference being that the top of the hopper is open permitting the free escape of water vapor or steam to the atmosphere. The water level should be carried within two inches from the top of the hopper.

Water when converted into vapor or steam absorbs a great quantity of heat, and of course the steam carries the heat of evaporization with it when it escapes to the atmosphere.

As the hopper is open to the air, the temperature of the cylinder cannot exceed 212° F. (temperature of boiling water) as long as there is sufficient water left to cover the cylinder.

The hoppers contain sufficient water for runs of several hours’ duration, and as the water boils away or evaporates, it may be replenished by simply pouring more water in the top of the hopper. Hopper cooling is used principally for small portable engines where the weight of a water tank or other cooling device would be objectionable and also where there is danger of freezing the pipes and connections of other systems.

The loss of water by evaporization is from .3 to .6 of a gallon per horsepower hour; that is, for a 5 hp. engine the loss would be from 1.5 to 3 gals. for every hour that the engine was operated under full load.

The cylinder and the water jacket are cast in one integral piece, with no joints of any kind in either the combustion chamber or in the water jacket.

Fig. 124. Air Cooled “Grey Eagle” Aeronautical Motor. Note the Depth of Cooling Ribs.

A system of cooling by which the heat of the walls is radiated to the air directly without the medium of water is often used on small high speed engines, and is known as “AIR COOLING.”

This type of cylinder is surrounded with radiating ribs or spires which increases the radiating surface of the cylinder to the extent that the required amount of heat is lost to allow of economical lubrication. This system is desirable where the weight of radiators and water would be a drawback, where it would be inconvenient to obtain water, or where there would be trouble from freezing. An air cooled motor generally is provided with a fan that increases the efficiency of the radiating surface by changing the air between the ribs. With aeronautical motors such as the Gnome, and Gray Eagle, shown by Fig. 124, the circulation of the air due to the propeller and the rush of the aeroplane is sufficient to thoroughly cool the machine.

As a rule, the air cooled motor is made more efficient in fuel consumption than the water cooled type because of the high temperature of the cylinder walls. In fact all engines are air cooled eventually, whether the heat is radiated at a high temperature by the fires, or at a lower temperature through the circulating water and radiator.

When the engines are of the portable type, and likely to be used out of convenient reach of water, the hopper or EVAPORATOR TANK system is used, the tank system being used for the larger engines. In effect, the tank system is the same as the hopper cooler, the heat being dissipated principally by evaporation, although some heat is radiated from the surface of the tank itself. The difference between the two systems is merely one of size, the tank offering a greater area for the emission of heat than the hopper.

A tank-cooled engine has one pipe running from the top of the cylinder to a point near the top of the tank, the bottoms of the cylinder and tank being connected together by another pipe.

When the water becomes heated in the cylinder, it expands and becomes lighter than the cold water in the tank and consequently rises to the surface of the water in the tank through the upper pipe. As the warm water flows into the tank, it is immediately replaced by the heavier cold water that flows into the cylinder from the bottom of the tank through the lower pipe. This successive discharge of the heated water from the cylinder to the tank sets up a continuous flow of water through the water jacket of the cylinder, which transfers the excess heat of the cylinder to the tank where it is dissipated to the atmosphere by evaporation and radiation.

The circulation of the cooling water set up by the action of heat or the expansion of the water is called Natural or Thermo Syphon circulation.

Cooling tanks may be used profitably with stationary engines if the tank can be located so that vapor and steam produced will not be objectionable. If the tank is used inside of a building, the vapor should be conveyed to the outside air by means of a stack or chimney, or by means of a small ventilating fan driven by the engine.

The water consumption of a cooling tank is from .3 to .6 gallons per hour, the exact quantity varying with the atmospheric conditions and temperature.

Fig. 124-a. De Dion Bonton “V” Type, Air Cooled Aero Motor. The Cooling Air is Furnished by a Blower Mounted on the Crank Shaft at the Rear of the Motor. The Propeller is Driven from the Cam Shaft. Courtesy of Aero.

For engines of from 10 to 50 horsepower a battery of cooling tanks may be used, the number depending on the size of the engine. For natural circulation, the tank should be installed so that bottom of the tank is above the bottom of the cylinder for maximum results, if placed much lower the engine should be provided with a circulating pump.

If water is used from the city mains from 10 to 15 gallons will be required per horsepower hour, the exact quantity varies with the temperature of the supply.

The water from very large stationary engines is cooled by allowing it to trickle down through a cooling tower, which is built somewhat like the screen cooler only on a larger scale. The object of the cooling tower is to present the greatest possible surface of water to the air, this is accomplished by screens or baffles that turn the water over and over as it falls. The water, well cooled, finally collects in a cistern at the base of the tower from which it is pumped back to the engine and thus is used over and over again. This is an ideal system when water is expensive and when engines of considerable power are used.