The Gasoline Motor

by Harold Whiting Slauson

In view of the difficulty which has been experienced by many drivers in sufficiently lubricating the pistons without causing the car to emit clouds of smoke, it may well be asked, "Why cannot an unburnable oil be used and thereby eliminate this trouble?" This is out of the question, for the mineral oils now used are obtained from petroleum and are cousins of kerosene, gasoline, benzine, and many of the other highly-inflammable liquids that need but the touch of a match to burn almost with the rapidity of an explosion. But notwithstanding the excitable family to which the mineral oils belong, the modern motor car lubricants are removed a sufficient distance from their more inflammable relatives to enable them to withstand a temperature of between 400 and 500 degrees, Fahrenheit. This is sufficient heat-resisting ability to enable the oil to stay on the cylinder walls near the bottom of the stroke, where it is most needed; but even though its burning point could be raised to a degree double its present amount, it could not withstand the high temperature generated in the top of the cylinder at the time of the explosion. The temperature here reaches a point well above the 2000-degree mark, and were it not for the cooling system, parts of the interior of the cylinder would probably be melted by the continued application of this excessive heat.

Any oil, consequently, would find but small opportunity to remain in its normal state after it once reached a point at which it would be exposed to the heat of the explosions, and we must look for a preventive measure other than that of increasing the flash-point or burning-point of the lubricant. But this high temperature does not exist throughout the stroke, for as the piston descends and the gas expands, heat is given off until the oil on the lower portions of the cylinder uncovered by the piston is sometimes able to remain in comparative peace. And even though this oil remaining on the cylinder walls at the bottom of the stroke should be burned, it would not be present in sufficient volume to create the dense clouds of objectionable smoke. Consequently it is the endeavor of engineers so to design the pistons and lubricating system that excess oil will not be fed to the pistons and allowed to remain on the walls after the former have descended.

But an excess amount of oil fed to the cylinders will result in so much less harm than will an insufficient supply, that we are treading on rather dangerous ground when we warn the amateur to cut down his lubricant to the point where there will be no smoke. As there are no ordinances that absolutely prohibit the slightest appearance of smoke at the exhaust, and as a faint blue trail is an excellent indication that the motor is receiving sufficient lubrication in the cylinders, it forms a satisfactory test by which the novice can determine the condition of the oiling system.

By the time that the exhaust gases have passed through the pipes and have expanded in the muffler, some of the blue smoke may have disappeared, and consequently the fact that a car does not give a trace of vapor at its exhaust should not necessarily be taken as an indication that the motor is not well lubricated. If the owner would satisfy himself that the cylinders are receiving a sufficient amount of oil, he may open the individual pet cock on each, and if he finds there a faint blue trail of smoke at each explosion in that cylinder, he may rest assured that harmony exists between the rubbing surfaces of the piston and the cylinder walls.

With the increase in the size and power of the automobile motors and the proportionately greater number of parts demanding lubrication, the attention required from the driver by the oiling system has been greatly lessened. Instead of the necessity of turning on individual oil cups whenever the motor is started, the modern driver merely twirls the starting crank or presses the button of the self-starter, secure in the knowledge that whenever the motor runs, the lubricating system operates—provided, of course, the reservoir is filled and there is no stoppage in the pipes. The oiling system of the modern motor is absolutely automatic, and if supplied with a sufficient quantity of a good lubricant, it will perform its work with an absence of trouble that places it among the greatest improvements of the engine of recent years.

Individual oil cups such as were used formerly, have been eliminated from the cylinders, and whatever sight-feeds there may be are placed on the dash in plain view of the driver. Instead of relying upon the suction of the cylinders for the positive feed to the piston, mechanically-operated pumps are used to force the oil to the various portions of the motor. In some systems, there is a separate pump for each oil lead. This is known as a mechanical oiler, and generally consists of an oil tank located on the dashboard of the car—either in front of the driver, or under the motor hood—and connected by means of a belt or gear with some shaft of the motor. The belt or gear drives a shaft to which is connected the plungers of the various oil pumps that force the oil to the different parts of the motor. Before passing to the individual pipe, however, the oil drops through a sight-feed connected with that lead, and as all of these sight-feeds are mounted in a row within plain view of the driver, the condition of the lubricating system in part or in whole may be determined at a glance.

The parts of the motor that are lubricated by an independent feed line in this manner may vary with different motors. In general, however, it may be said that it is seldom that the oil is fed directly to the piston, but that the lubricant is first distributed to the oil wells in the crank case. Here, the splash of the cranks as they revolve in the oil is depended upon to throw the lubricant upon the exposed portion of the piston as it reciprocates below the cylinder walls. The sides of the piston thus covered carry the oil to the cylinder walls.

It is evident that if an excess amount of oil is continually carried up by the piston to the cylinder walls, a certain proportion of this lubricant will reach the open space in which the charge is ignited, and will there be burned—with the attendant formation of clouds of objectionable smoke. This trouble is overcome to a certain extent in some motors by the use of a type of ring set in the piston that prevents the lubricant from passing to the upper portion of the cylinder; but all the oil cannot thus be retained, and it therefore behooves the driver not to allow too great a quantity to be fed to the crank case if the "splash" system is used.

The main bearings on which the crank shaft revolves are generally supplied with oil by independent leads from the oiler, and when the above-described system is used they may be regulated independently of the splash feed lubricating pipes. Excess oil at the bearings will cause no damage, but each crank shaft journal does not demand as great an amount as that supplied to a piston and connecting rod bearing.

Many lubricating systems that are now in popular use employ but one pump to force the oil to the various bearings and rubbing surfaces, and regulate the supply by the size of the pipe leading to each. A satisfactory method of overcoming the possibility of excess oil in the cylinder has been adopted by some manufacturers. This consists in placing a channel, or trough, directly under the lower sweep of each connecting rod bearing. Each channel is kept filled to overflowing by a separate pipe connected with the main lead from the pump, and a constant level is consequently maintained at all speeds of the motor. An elaboration of this method consists in attaching one end of each trough to a rod operated in conjunction with the throttle, so that as the speed of the motor increases, the end of the channels may be tilted, with the result that the connecting rod scoop will dip deeper into the lubricant.