From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical article on lubrication for car maintenance, covering engine oil and the transmission system.
| Identifier | ExFiles\Box 145\3\ scan0017 | |
| Date | 13th February 1934 | |
| Reprinted from The Motor February 13, 1934. LUBRICATION—VITAL TO CAR MAINTENANCE—Contd. by forming sludge, increases the viscosity of the oil. Other points in which oils differ are the tendency to form carbon, the temperature at which solidification occurs, freedom from impurities, etc. Furthermore, while many lubricants are of the straight mineral type, others are compounded; i.e., they consist of mineral oils blended with fatty or vegetable products. These products tend to promote "oiliness"; a property difficult to define but one which is of special importance under conditions which prevent the formation of a true lubricating film. Routine attentions to the engine which are of great importance to proper lubrication are: (1) the maintenance of the correct oil level in the sump, (2) complete drainage of the sump at intervals and replenishment with fresh oil, (3) regular cleaning of the filters provided for cleansing the oil in circulation and for removing grit from the air entering the carburetter. Changing the Oil in the Sump The first of these points is not often neglected, but the second is apt to be shirked. It is certainly true that an engine can be run for very long periods without changing the oil, but it is equally correct to state that a change of lubricant at reasonable intervals will minimize wear to a marked extent. The oil itself does not "wear out" in use, but its effectiveness as a lubricant becomes seriously impaired through various causes, which may be enumerated as follow:—(1) Direct contamination by black carbon particles, by road grit and by metallic dust abraded from the bearings, piston rings and cylinders; (2) the mixture of the products of combustion with the oil, particularly water and certain acids; (3) dilution by liquid fuel which passes the pistons when a cold engine is started; (4) oxidization produced when the oil, at high temperatures, is mixed with air in the crankcase. In bad cases—particularly when an engine becomes worn—water which gets past the pistons in the form of steam may emulsify with a dirty oil to form a sludge. This process of deterioration can be offset to some extent by a thorough filtering system, always supposing that the owner-driver will take the trouble to clean the filtering medium at regular intervals. Filtration cannot, however, remove the petrol which dilutes the oil, nor can it prevent oxidization, so that even under the best conditions the need for draining the sump at intervals remains. In the case of a new engine frequent drainage is particularly desirable, as metal abrasion may be rather severe. Dilution of Oil by Fuel The extent to which dilution by fuel occurs depends upon working conditions, the use made of the strangler, the fuel employed, and the fit of the pistons and rings. An oil with a normal viscosity figure of 225 seconds at 140 degrees F.{Mr Friese} will be "thinned" to a figure of 100 seconds by the admixture of petrol to the extent of 10 per cent. Under working conditions involving frequent stopping and restarting this degree of dilution may occur in the course of 500 miles or less; luckily, it becomes offset by re-evaporation of petrol from the sump, so that, after a certain stage is reached, further dilution occurs only slowly. In the ordinary way it should suffice to drain the oil through the plug or tap provided after placing the car on a level floor. Flushing oils can be used with advantage to ensure thorough cleansing. When the chassis is due for overhaul, however, it is a good plan to have the sump entirely removed, so that it can be properly cleaned internally. The temperature which the oil attains on a long run represents the balance between the rate at which it is being heated and the rapidity with which this heat can be dissipated. The former will be at a maximum when the engine is working hard, so that under high-speed cruising conditions it is very desirable that the oil should be given every chance of dissipating the heat which is produced by friction and by conduction from the hot pistons, etc. For this reason it is essential to maintain the proper level in the sump and to ensure as free a flow of air around the outside of the sump as is possible. Number plates and other parts should not be so placed as to baffle the lower part of the crankcase, and the external surfaces of the sump should be kept free from deposits of mud and grease, which tend to prevent the heat from escaping. Special devices for cooling the oil have been used on certain makes of car with success. While adequate oil cooling is important to the safety of the working parts under cruising conditions, it is equally desirable, for reasons already mentioned, that the oil should warm up rapidly after a cold start. Thermostats are of great value in enabling the cylinder jackets to reach an efficient temperature without delay, but, even so, the oil warms only sluggishly. Consequently, a cold engine should be treated with consideration and not driven “flat-out.” Engine Speed When "Warming-up" On the other hand, too low an idling speed, when a cold engine is allowed to run before the car is driven off, will curtail the amount of oil flung up into the cylinders; the throttle should be set to give a speed of 1,000-1,200 r.p.m. (about four times a slow idling speed), and the mixture control, or strangler, should be set at normal as soon as possible. From the comments on oil pressure gauges made earlier in this article it will be appreciated that these devices, while giving a certain amount of information, cannot guide the owner as to the oil level in the sump until this reaches a dangerously low condition. Consequently, there is much to be said for the type of meter, fitted to the facia, which indicates the sump level. Another fitting of great utility, which is, however, seldom employed, is a thermometer connected to the sump which shows the driver the temperature of the oil. In concluding this section of the subject, special mention must be made of the process of running-in a new engine, as this is of the utmost importance to the subsequent life of the car. Bearings, pistons and cylinders attain a burnished surface in use, which is very much smoother than that produced even by the most careful manufacturing methods. Consequently, a new engine tends to turn stiffly, and creates a great deal more internal friction than one which has been properly run-in. It follows that the surfaces should not be overloaded and that they should be safeguarded by adequate lubrication. Latterly, considerable success has attended the use of special running-in compounds, consisting of oil containing colloidal graphite. These lubricants are fully described later in this article. LUBRICATION—VITAL TO CAR MAINTENANCE—Contd. Under particularly arduous conditions oils containing colloidal graphite have been used with good results and for hypoid gearing, where the tooth pressures are extremely high, several oil concerns have produced what are called E.P. lubricants ("excessive pressure") containing various chemical dopes designed to maintain the film between the gear teeth. Axle and Gearbox Drainage Although not suffering from as many sources of contamination as the oil in the engine, gearbox and back-axle lubricants become loaded with metal particles in the course of time, while the fairly high working temperatures promote oxidization. Consequently, regular drainage and replenishment are highly desirable. The parts should be drained just after a run on the road when the oil is hot and is therefore in a condition to flow freely. The Transmission System MANY of the general remarks which we have made regarding the engine apply equally to the gearbox and the back axle. Thus, too thick an oil will increase the drag and friction at low temperatures, whereas a lubricant which is too thin will tend to escape (by leakage) and may not provide efficient lubrication under arduous working conditions. Advice as to the correct grade can always be obtained either from the car maker or from the leading oil concerns. Synchromesh and Free Wheels In 1934 models synchromesh gears, the free wheel and the Wilson self-changing gearbox are being widely used, and these have, to some extent, influenced the choice of lubricant for the transmission. Thus for synchromesh boxes and free wheels it is usually recommended that an engine oil or a light gear oil should be employed instead of the heavy gear oil so often used in the past. Too thick a lubricant will interfere with the proper working of the small cone clutches employed in the synchromesh mechanism and may also obstruct the action of the rollers in a free wheel. The self-changing gearbox, in addition to the epicyclic gear wheels, contains a set of friction brakes (operating upon drums), by means of which the various gears are selected. This brake mechanism—lined with friction fabric—is immersed in the oil, and for this reason special lubricants have been evolved to meet the conditions. Obviously, the oil will become heated by the action of the brakes and its qualities as a lubricant will influence the smoothness with which the brakes operate. The owner-driver can ensure good results by studiously avoiding brake slip, by using a recommended lubricant and by draining and refilling the box at regular intervals as recommended in the instruction book. Back-axle lubrication calls for little comment beyond the remark that if the car owner experiments with lighter oils than are usual he must keep a particularly watchful eye upon the oil level in the back-axle casing. Thick oils, generally speaking, increase friction and reduce noise. Excessive lubrication should be avoided as the oil will then find its way past the sealing devices and may reach the brake drums. Another part of the transmission requiring special attention is the propeller shaft, which is usually equipped with a mechanical type of universal joint at each end. These joints are lubricated with grease, and it is most important that this should be of a special non-separating composition, to withstand the centrifugal action. Before leaving the transmission mention must be made of the need for lubricating the clutch spigot bearing and, in some cases, the withdrawal gear in accordance with the car maker's recommendations. For the fluid flywheel the Daimler Co. supplies a special light mineral oil. Image Captions: Graphical record of a one-hour run (starting from cold) on a six-cylinder car with thermostat control; note that although the water temperature is fairly steady throughout, the warmth of the oil increases very slowly. Novel method for cooling a big-end with fins, used by an American maker. A neat rear-axle (Lagonda) in which a spring-loaded rod is raised to open an orifice at the correct oil level. This must be closed before the filler plug can be replaced. | ||