SAVING PETROL

Southland Times, Issue 20615, 13 October 1928, Page 17 (Supplement)

SAVING PETROL

LOOK OUT FOR LEAKS. A driver is often too apt to assume that the carburetter is to blame for a high consumption of fuel, whereas there are very many other possible and probable causes for this defect. One of the most common is simply leakage; petrol is allowed to escape from unions, taps and flat chambers in small quantities, but continuously, so that the total amout wasted is by no means inconsiderable; again, quite a lot can be spilt every time the tank is replenished by a careless garage hand. Leaks at joints may be so slow that the petrol evaporates almost as quickly as it runs out, so making it difficult to detect. Then there is the float chamber of the carburettor, which maintains a constant level, or is, at any rate, supposed to do so. Here a leaky float, dirt under the needle, or any stickiness in the action of the mechanism may allow the petrol to rise up and flood over through the jets and at the point between the float chamber and lid. The process of tuning the carburetter is one which few owner-drivers are competent to carry out, but, apart from the jet which governs the mixture supplied to the engines when the throttle is open, there Is the slow-running mixture, which has a more potent effect upon the petrol consumption of the car that most people imagine. This Is because whenever the throttle is closed to allow the car to slow down, or when running down-hill it is the slowrunning jet which controls the amount of petrol drawn into the rapidly moving engine. CAUSES OF EXCESS OIL PASSING THE PISTONS When the amount of oil passing the pistons is greater than can be burned, it may be due to two conditions; first, because too much oil is thrown to the pistons by the lubricating system; second, because the design or the fit of the piston and rings is such that top much oil is allowed to pass by them into the combustion chamber. Both conditions are common. The type of lubricating system employed is important in determining the amount of oil delivered to the cylinder walls, for in some types the amount may vary widely during the life of the engine, while in others it remains fixed, and depends upon the design and proportion of the parts. Characteristics Of The Splash System. In all systems employing connecting rod dip with a constant level in the splash troughs, and where the crankshaft is not drilled for delivery of the oil under pressure to the connecting rod bearings, the amount of oil thrown to the cylinder depends upon the depth of the dip of the connecting rod or the scoop attached to it. Where the scoop is of the correct design, and the dip not excessive, no trouble from this source need be expected. However, in such systems, due to faulty design, it is by no means uncommon for the scoon to be of such size that it dips too deep. Sometimes a condition is encountered where extra long connecting rod bolts were fitted through some error, and in addition an excessively long scoop was used. The result was excessive splash, abnormal oil consumption, carbon trouble and plug fouling, all of which were overcome when the resign was changed. Characteristics of Force Feed Lubricating Systems. The Force Feed Lubricating System supplies oil to the connecting rod bearings through drillings in the crankshaft. The rods do not dip into the oil. In this type of system, the amount of oil thrown off by the connecting rods depends upon several things. First, the pressure set up by the pump. Second, the clearance of the bearing*. Third, the engine speed. Fourth, the body of the oil. For a given oil body, the larger the bearing clearance, the greater the flow of oil, simply because we have a larger oil outlet. There is one popular misconception in regard to Force Feed Systems which often leads to oil pumping troubles in engines which would otherwise be free from them. This idea is that high pressures are essential to lubrication, and that low pressure is a certain indication of lack of lubrication. To illustrate the point more fully, when a car is new the lubricating system usually shows high pressures. After a varying period of service, the pressure begins to run low’er until after twelve or fifteen thousand miles it may indicate only half the original amount. Following the usual instruction book recommendation of a fixed pressure, the tendency is to make an adjustment of the oil relief valve to restore the pressure to normal. What, is the result ? Over-Filing almost invariably. The condition may well be compared with a water system. When all the outlets are closed the pressure is high, but as the outlets are opened and water begins to flow, the pressure is relieved and the greater the flow, the lower the pressure. In an engine with tight bearings, there is little flow through them, and the pressure is high. Must of the oil escapes through the pressure relief valve. When the bearings loosen more oil flows through them and less through the relief valve. The pressure drops. The remedy, if too much oil : is being thrown to the cylinders, is to still I further reduce the oil pressure by adjustment of the relief valve—or by-pass as it ! is sometimes called—so that it discharges j more oil. i Many cases of over filling in passenger ’ car and truck engines can be overcome this way. In fact, unless the bearings have loosened to such an extent that they knock, in order to cut down the oil flow, it is advisable to try the effect of reducing the oil pressure before taking up the bearings. Pome force feed systems have special control devices, such as a valve inter-con-nected with the throttle or actuated by the intake manifold vacuum. These regulate ] the oil supply to the speed of the engine, tin excellent feature, as will be appreciated in view of what has been developed earlier in this article. Where such devices are employed the excessive leakage experienced > with badly worn bearings is materially re- • duced. —Engineering Division, Automotive Department of the Vacuum Oil Company Pty. Ltd. COIL IGNITION LOCATION OF TROUBLE. TWO-POINT SYSTEM. It has been known for many years that, by the use of several sparks occurring at precisely the same instant in the charge compressed in an engine cylinder, the power produced is increased over that developed by a single spark. The engine runs more smoothly, and a leaner and more economical mixture can be successfully used. About fifteen vears ago a few passenger cars were brought out with engines having rwo-boint ignition, from special twin spark magnetos, but this system did not continue in use. Multi-point ignition has been in general use on large stationary engines since its invention. Renewed interest in this ignition method has been aroused by the recent introdution on current models of two-point ignition, derived from two pairs of exactly synchronized breaker points, two coils, two condensers, and a high tension distributor cap, with two segments for each cylinder, from which cables run to the two plugs, found one opposite the other in each combustion chamber. The engine thus has two practically separate ignition systems, and will run on either of them if the other fails, the battery, the switch, and the high tension parte of the distributor cap, tension parte of the distributor being the only units common to both systems. Besides increased reliability this twinspark system has the advantages of improving acceleration- and fuel economy combustion being more nearly complete when the charge is ignited at two points than at one i only. Careful tests indicate that two-point

ignition increases the output of an engine, or enables the same output to be obtained with less expenditure of fuel. When Ignition Fails.

In case ignition fails completely, or is irregular on all cylinders, and after all wiring and its connections have been looked over, the battery found to be alive, the switch contacts proved to be perfect and the breaker points and sparking plugs tested, the coil and its related devices come under suspicion.

To test the coil, put the switch on, disconnect from the centre terminal of the distributor can the high-tension cable which comes from the coil, and hold its detached end slightly more than one-eighth inch from the metal of the engine, while someone cranks the engine by hand. If a normal appearing spark passes from it at regular intervals, the coil and condenser are presumably all right. Should no spark occur, watch the ammeter and see if it indicates a discharge of several amperes, when the ignition switch is put on. If it does, current is flowing in the primary of the coil, but if it does not the primary circuit in broken. All other parts of the circuit having previously been found in order, it is possible that the resistance unit (located on the coil, or on the distributor head) is opencircuited.

If bridging its two terminals with a short piece of wire causes the ammeter to register discharge, the resistance has failed, and must be replaced; but the engine can be run, in an emergency w'ith it cut out by short-circuiting it. In case the circuit cannot thus be restored, and the breaker pointe are together in good electrical contact, a primary terminal is disconnected from its winding or the orimary winding itself has failed —a very unlikely but possible happening—calling for a new coil. If the ammeter shows current passing through the primary circuit, but still no spark is obtainable, watch the ammeter, as the engine is very slowly hand cranked, and see if its needle drops to zero for an instant each time the breaker points separate. Where the Trouble Lies.

This being the case the primary ignition circuit is functioning properly and the trouble ie that the fine wire secondary winding is open-circuited or short-circuited, which means replacing the coil. But if the primary current does not fall to zero instantaneously, when the breaker points separate, it indicates that the condenser (found on or in the distributor unit or on the coil) has broken down, and thus completes the primary circuit around the breaker point. A new condenser is the remedy. If a condenser loses its connection around the breaker points, ignition will usually fail entirely, even if all other parts of the system are in order, although weak sparks sometimes will continue to be produced, with considerable flashing and burning at breaker points. Irregular and weak engine operation sometimes proves to be due to a condenser which has lost part of its capacity or a coil secondary that has defective insulation. FIRE RISKS WARNING TO SMOKERS. A number of Auckland service stations have erected conspicuous notices warning motorists against smoking while petrol is being handled. Quite a number of drivers ignore the caution, apparently on the ground that a good customer should not be inconvenienced. The fact that one regularly buys a few gallons at a profit of 3d a gallon) from a certain station does not entitle one to start a fire. Motorists generally believe that the warning is intended as a protection for the garage. On the other hand it w r ould be quite possible for the car to suffer most from the consequences of a carelessly thrown match. It has been proved in fires in Auckland that it is possible for a pump to be enveloped in flame without igniting the bulk underground. It is true that a cigarette will go out if dipped in petrol, but this does not prove that the glowing end, or sparks therefrom, will not ignite petrol vapour. Tests have shown that this may occur quite readily. The folowing authentic case shows the vapour danger. A man was washing his overalls in a mixture of petrol and hot water, 40 feet from an open coke stove. The vapour from the spirit permeated the air to such an extent that a flame flashed back to the stove, severely burning the man concerned. The greatest care should always be taken not to leave cans of petrol without the stoppers securely screwed down, and thus to insure against evaporation. There are very many things which may start a motor-car fire on the road, but perhaps the most common is popping back through the carburetter due to a weak mixture, this being apt to set the float chamber on fire. Quite possibly the flames will get blown if the engine is raced on full throttle, but if the owner has neglected to remedy petrol leakages at joints in the fuel system, far more serious damage may be done. Leaky unions permit petrol to drip down into the engine, and vapour may collect under the bonnet to a dangerous extent. Another point to remember is that great care should be exercised when replenishing a scuttle tank, the filler of which is placed under the bonnet. Very often petrol will splash on to the hot engine and will become vaporized, ready to start a fire should a spark be produced by the ignition system, or even if the person filling -the tank is smoking. Short circuits or electrical leakages can often be detected on the ammeter before damage is done. The procedure is to switch off the current, but this will, of course, effect nothing if the short circuit is between the switch and the battery. Occasionally the heavy cables lose their insulation and become crossed or grounded near the self starter. The bright sparks which result are not without risk if there has been flooding in the carburetter. The majority of motorists in Auckland visited the fire which burned for several days in an oil store at Freeman’s Bay, and it must have been brought home to all how futile is the use of water on blazing petrol. One of the oldest methods of extinguishing burning liquids is the use of sand or damp earth, thrown in sufficient quantities to prevent air reaching the combustible matter. A disadvantage of this method, however, is that, in the case of a tank or container of liquid, sand or earth would simply sink to the bottom and would, therefore, have no effect. This sand would only be of use where the burning liquid was spread evenly in a very thin layer over a comparatively level surface on which the earth could be thrown. Even a fairly serious outbreak can often be smothered with a rug or thick overcoat, • but, alas, often with damaging results to j the article in question.