LUBRICATING THE MODERN MOTOR-CAR ENGINE

Wanganui Chronicle, Volume 71, Issue 291, 8 December 1928, Page 21 (Supplement)

LUBRICATING THE MODERN MOTOR-CAR ENGINE

(By courtesy of The Shell Co., of N.Z., Ltd.) This is the second part of a series of three articles on this subject, the first article having been published in our issue of Saturday, December I. Part 2. Carbon.—One of the wellknown non-metallic elements. Both lubricating oils and motor spirits arc chemical combinations of hydrogen and carbon. Therefore, here will be mentioned the question of carbon deposits from motor spirit as well a.s from lubricating oil. Four different sources arc the cause of carbon deposit in an engine:—

1. A low grade of lubricating oil. 2. Too much lubricating oil. 3. A badly adjusted carburettor giving too much motor spirit. 4. Incomplete °ombustion of motor spirit. Often car owners blame the oil they are using for carbon deposit, whereas the deposit is actually solids drawn in through the carburettor with the air, and, becoming loaded with lubricating oil and motor spirit, they are deposited on the heads of the pistons, cylinders and valves. Analysis has proved that 95 per cent of the deposit commonly called carbon is elements from the atmosphere. In country suJi as the .Mallee and north of Victoria, the deposits inside a motor car engine should be greater than in a car run in Gippsland or Tasmania, owing to the ii creased amounts of solids in the iorm of dust in the atmosphere. Motor car designers arc .eliminating this difficulty to a great extent by fitting air fitters. Dilution.—Any motor spirit finding its way into the crank ease or sump of the engine will bring about dilution of the lubricating oiJ. If, owing to an incorrectly adjusted carburettor, motor spirit enters the engine in liquid form instead of in the form of vapour, the motor spirit will find its way into the crank case, and, occasionally where the temperature of the walls of the engine, say on a cold morning is sufficiently low to cause condensation of the motor spirit vapour coming in contact with the cylinder walls, the condensed spirit will find its way to the crank case. It requires a small percentage to dilute the lubricating oil to such an extent that it loses viscosity; thu s the oil film is rendered ineffective as a lubricant. The most direct way to find out whether dilution is taking place is by testing its viscosity as already mentioned ider the heading of “Viscosity.” However, a very simple test i s to get a small quantity of the crank case oil between the thumb and finger of one hand and compare it with new oil between 'he thumb and finger of the other hand. Badly diluted crank case oil is strong smelling, thin and generally a distinct black colour. Another method ,f judging when to change the oil is to note the pressure on the gauge after the engine has warmed up and is running at 25 m.p.h. If the pressure, after filling with fresh uil, is noted and later, under similar running conditions, it falls to halt that value, tho oil should be changed. This cannot be taken as an absolute rule, and should be supplemented by the judgment of the driver after he takes into consideration tho condition of the pump and its various connections.

It will not be long before the motor manufacturers will fit some such device as the “.Skinner fuel and oil rectifier.” This device not only abstracts any motor spirit that has passed down the cylinder walls and thus preserves tho viscosity of the lubricant, but it also returns the motor spirit to the combustion chamber in a vapo .rised form, and so will give greater mileage to the ga.llon. Using the choke too much, flooding the carburettor or opening up the throttle too soon after the engine ceases, creates dilution, which is the greatest enemy of lubricating oil. Un vapourised motor spirit runs down past the piston, it destroys the seal between the piston rings and cylinder wall, removes the oil film which is to protect the surfaces of the cylinder, piston, cam ami crank shaft bearing from cohesion, and, last, dilutes the lubricating oil in the crank case to such an extent that it becomes worthless. If an engine runs stone cold, as some makes are known to do, then it will pay the motorist to blanket part of the radiator, and so increase the heat of the engine, especially in cold weather; otherwise poor vapourisation will result, and it will be necessary to frequently drain the crank case to prevent serious damage to tho. cylinder walls and bearings. Provided that a good oil is being used and the oil pressure is correct at starting but falls off to a very marked extent when hot, thi s indicates any of throe things: 1. Crank case dilution. 2. Dirt under sump valv.es and dirty strainer. 3. Leaks in the oil pump or various connections. In engines equipped with force feed lubrication, should the pistons, piston rings, and cylinder walls be worn and dilution is taking j lace, a heavier grade of oil than that recommended by the users should be used. It is also very important in thi a case that fresh oil should be added each morning, and the level kept up to the full mark. Every shilling spent in oil will save pounds in the repair bill.

Tn the case of the Ford Model T engine, a much heavier grade oil would not be advisable, owing to the fact that all points of the power unit, which includes multiple ype disc clutch and magneto, are lubricated with the same oil. Therefore a clutch, etc., of this type would fail to work highly satisiaetorily with an oil of a heavier grade. Cooling the Lubricating Oil.—lt is just as important to pass the oil through a radiator to cool it down before pumping through the engine as it is to cool the water system. Tho following cylinder temperatures are given by Rankin Kennedy, C.E.:

Maximum temperature in the cylinders at the top of the explosion stroke is approximately 2700 deg. F.; minimum temperature during the suction stroke is about 250 deg. F.; average temperature during the four strokes of a four cycle engine is about 950 deg. F. These are the temperatures in the cylinders to which the outer side of t . oil film is exposed. The oil in contact with the cylinder walls and pistons is kept below the flash point (of about 500 deg. F.) by being in contact with watercooled metal, which conducts the heat away. Therefore onty the outside layer is actually in contact with this excessive heat and subject to the burning action of the explosion. If the oil is previously cooled in a radiator, it will be in a better condition to resist the heat it is being subjected to. In some of the. better types of cars now being 'manufactured, special radiators for fho cooling of oil is a standard equipment.