MOTORDOM

Greymouth Evening Star, 6 November 1931, Page 4

MOTORDOM

NEWS OF THE ROAD

(By

“Gearbox”)

LONGER LIFE FOR TRACTORS

There is a well-known saying in the paint world, "Save the Surface and vcu Save All.” This truth also applies to the rubbing surfaces of engines, particularly tractor engines, where fuel used is kerosene. The right oil. .rightly used and maintained in good condition, will save the rubbing surfaces, and thereby save all. The fundamental purpose of a lubricant is to prevent metal-to-metfil contact—i.e., it has to maintain a strong protective film between pistons, piston rings, valve stems and valve guides, cams and push-rods, and all bearing surfaces. The problem, therefore, is to protect the oil, to maintain it in good condition, and thereby secure economy in long engine life and freedom from repair bills. The most dangerous enemy to tractor crankcase oil is dilution. This enemy works unseen, and unheard. Dilution reduces the viscosity or “body” of the oil. This in itself is bad enough,, because the protective oil film becomes dangerously thin for its work of preventing metal-to-metal contact. However. an accompanying evil is the reduction in the oiliness property of the lubricant. When kerosene mixes with oil,.the fluid film separating the rubbing surfaces breaks down under less severe operating conditions than when undiluted oil is used. The following are four good rules: Do not switch over until the engine is warmed up: do not idle unnecessarily on kerosene: observe the regular GO hours’ oil draining period : use a power Uerosene, free from non-vaporising, non-burning portions. Prevention is letter than cure, and it is the fourth item that has the strongest effect in minimising oil dilution.

HOW TO TEST KEROSENE Some idea as to a kerosene’s readiness and completeness of vaporisation can be obtained by noting how quickly the tractor will pick up the load, and how flexible the engine is under working conditions. However,- there is one sure test, which is quite simple and which we recommend to every tractor owner who is concerned in keeping oil dilution down to a minimum. Take samples of the various power kerosenes available to you, and pour a few drops of each on to rusty plowshares. Place these out in the sun and note which kerosene for your tractor operations, because, by using one which will evaporate readily and completely under this test, you will secure ready and as complete as possible vaporisation in your tractor; ■ thereby preventing the introduction of liquid fuel into your engine. By using a good volatile kerosene, i.e.. one which will vaporise readily and completely, you will keep dilution down to a minimum and secure economy through long trouble-free engine life and the elimination of repair bills, which are nearly always due to breakdown of lubrication. OIL PRESSURES Motorists, as a general rule, are under the impression that if a good pressure reading is showing on the oil gauge all is well with the lubrication system of the engine. In order to avoid being misled by this instrument it is essential that one should have a good idea as to what it is really indicating. The reading on the oil , gauge simply shows the pressure against which the oil pump is working. If there were no res.istance at ill no pressure would be registered, which would be the condition if a mam oil pipe should fracture. The pump has to create pressure in order to make the oil follow its path to the bearings, and this pressure is registered on the inter-connected gauge. In order to prevent excessive pressures from being created when the engine is cold a spring loaded relief valve is fitted, which by-passes some of the oil back to the sump until the lubricant warms up and the pressure falls. Sometimes the by-pass is restricted so that the pressure is much higher than normal for some minutes after a cold start. Then, as the oil warms up and thins, the pressure should fall slowly to a normal figure, which naturally varies with the spee‘d of the engine. Excessively high pressures may indicate that the relief valve has stuck in the closed position or may be due to dirty oil or sludge. Other common faults which give a high reading are a clogged delivery filter, or partially blocked oil In an engine where the gauge is connected to a bearing at the end of the system remote from the pump, a clogged filter or main pipe will then be indicated by a drop in the pressure reading. In some engines a lower pressure is registered when the oil level in the sump,is reduced towards danger point. Whether or not this will occur depends upon the position of the pump and the suction pipe through which it draws lubr.cunt. In other cases a low level in the sump is shown by sudden flickering movements of the oil-gauge needle when descending a steep hill or during a sudden braking; the small quantity of oil surges away from the suction pipe, leavihg it momentarily uncovered. Should the oi.l-gauge needle suddenly drop to zero at any time, this is a true danger signal usually indicating that the main oil supply pipe has frac> Lured. Faults in the oil gauge itself or in the pipe connecting the gauge to the lubricating system are sometimes the cause of erratic readings. A .simple test can be made by disconnecting the pipe that leads to the gauge (from the engine end) and then allowing the motor to idle, note whether oil spurts from the orifice. If the pressure has failed no oil will be delivered. The pipe to the .gauge in the course of time may Become partially .lilpcked with sludge, which is usually indicated-by . sluggish movement of ths. instrument needle, and after the engine Ifas- started, a short time will elapse before the gauge begins to show . pressure..' When the engine is cold it; should be allowed to run quietly fori a fiille lime until the pressure has risen to a normal figure.

VALVE TROUBLES DIAGNOSED

A sticking valve causes misfiring, and is likely eventually to bring the car to a standstill with all the symptoms and smother of violent overheating. The cause may be in the weakness of the valve springs, in the use of incorrect lubricant or fuel of poor quality, or in prolonged driving at speed. Inlet and exhaust valves, being raised by the powerful direct action of their cams, rarelj r fail to open as intended, but as they are closed by their springs—the force of which is far less positive—they do sometimes stick open, either failing to seat at all or seating too slowly to accomplish their purpose. Practically speaking, inlet , valves do not give this trouble, as they “run relatively cool, and their stems usually receive some lubrication and do not carbonise badly, but exhaust valves operate extremely hot, and whatever engine oil reaches their stems soon carbonises on them in a sticky state. When an exhaust valve fails to close or to close promptly enough, the fuel charge, which should be trapped above the piston and compressed on its upstroke, is pushed out instead of through the exhaust port. Burnt gas, instead of charge, is drawn in when the piston goes down on the suction stroke, with the result that reduced fuel charge and the exhaust gas present in the affected cylinder forms a mixture too weak and foul to be ignitable, and the cylinder misses fire. A misfire from this cause is often mistaken for one caused by failure of the ignition system, and it is difficult to prove that ah exhaust valve is holding open, as it will very often fail to do so when a test is made by hand-cranking, while it will do so when the engine is at speed. Very often the cause of a valve sticking open is that the clearance space between its stem and the guide in which it operates becomes filled with burned oil to such an extent that the spring is powerless to make the valve close against the friction which is thus set tip. This trouble can be reduced by installing one of the suction auxiliary cylinder-wall lubricators, which continuously introduce into the intake manifold small measured amounts of a special heat-resisting oil capable of surviving the combustion period, reaching the exhaust valves, and settling upon their stems to act in a lubricating and cleaning capacity. Another method for engines the lubricating systems of which permit it is the occasional sucking in of kerosene through the carburetter air intake. This acts as a solvent of gummy, carbonaceous material wherever it reaches.

Weakness of the springs is the other usual cause of the holding open of valves. Unless the springs which close inlet and exhaust valves retain their original strength the valves may not close, especially if their stems become sticky or heavily carbonised, and this holding open causes missed explosions. Even if they close, but do so sluggishly and too late, as may happen at high engine speeds, power and smoothness' of operation is sacrificed. Occasionally an improperly tempered spring may be assembled into an engine or the engine may accidentally become so greatly overheated that the resilient qualities of its valve springs are permanently diminished. A spring thus affected takes a “permanent” set, becomes shorter, and exerts an insufficient seating force upon its valve. When a certain cylinder is found to miss, and this cannot be explained in any other way, the following test will indicate whether or not the suspicion that it has a weak exhaust valve spring is well founded. With the engine idling the valve compartment cover removed, insert a screwdriver blade between coils of the spring and increase the valve closing effect by lifting on it. If this stops missing, it is evidence that the spring is too weak to be effective. When the springs are removed in the process of grinding valves it is a suitable occasion to test them as to strength. Stand them in a row and note if some are shorter than others. The shorter ones may nroperly be suspected of being below normal strength. If. one had a spring of exactly the same kind, which has never been used, or can ascertain the correct length of the particular kind of spring in question, it is an easy matter to find which, if any, have settled in use to a material extent. The best test of a valve spring is whether or not it is compressed a specified amount when a specified weight is imposed upon it, and most authorised service stations have this data for their product and convenient testing apparatus. ' - BABY CAR’S PERFORMANCE. At Brooklands, recently, a singleseater Morris Minor covered a flying mile at over 100 miles per hour, in both directions. This was rightly held to be a meritorious performance. Word has now been received that the same car, without super-charger, has put up an even better performance. Under R.A.C. supervision and observation, it covered miles on one gallon of petrol. This feat was accomplished on ordinary main roads, and the side valve engine was fitted -with a standard carburettor, incorporating a standard needle setting. A standard camshaft was also employed. This is proof of the efficient design of this chassis.

BRAKE EFFICIENCY “The brakes were applied, but they failed to act.” How-often is this excuse offered in accident cases? , The ability to: control the speed of motor-cars and bring them to rest in emergencies ' in the shortest possible distance is of paramount importance, and is intimately connected with the comfort and security of motoring, whether it be for pleasure or business. In these days of high speed, congested roads, inexpert drivers, and careless pedestrians, a motor vehicle with inefficient brakes constitutes a definite source of danger to its occupants and to other users of public roads —hence, the condition of the brakes of their cars should be the-first consideration of all motorists. Unfortunately, such simple precautions as attention to ad-1 justmeut of shoos and the lubrication of bearings and connections in the brake mechanism are often overlook-1 ed, and brake power when most re-i

quired is not always forthcoming, and we read of such instances as “the brakes were applied but they failed to act.” But they would have acted if the controlling mechanical parts had received reasonable attention. The remedy for inefficient brakes is simple, and easily effected, and, provided the brake lining is not unduly worn and is free of lubricant, all that is necessary is to adjust the shoes as closely as possible to the drums, without actually rubbing in the “off” position—and to make sure that all rods, levers, and bearings are lubricated and working freely. All cars with brakes acting on front and rear wheels should exhibit at least GO per cent, efficiency, and should be capable of being stopped on a dry level road in the distances at different speeds as under: — Miles per hour, ’ Stopping when Brakes Distance are applied. (Ft.) 20 .... 22.3 30 .... 50 40 .... 89 45 .... 113 BRAKE NOISE—SQUEALING This unpleasant feature is caused, in general, by the vibration of drums when the brakes are applied. Some drums are acoustically better designed than others to communicate vibration to the surrounding air, i.e., drums that have no flange at the open end. In such case a stout metal band clamped round the outside of the drum will alter the natural period of vibration, and is an unfailing remedy. Where souealing is intermittent, and not persistent (it may occur during and after wet weather) —here the cause is, in the majority of instances, an abnormal rise in the coefficient of friction due either to the entry of grit dr the formation of rust on the working surfaces of the drum, and usually disappears after the first application of the brakes. If the friction of the linings is reduced by the application of a little dry powdered graphite, squealing generally ceases, but the amount of graphite applied to the lining must not be overdone, otherwise the power of the brakes will ,be affected seriously. Another —and, perhaps, the most effective cure —is to dismantle the drum and shoes apd clear the surfaces of any deposit and chamfer off the surface of the lining with a file for about one inch at each end While an application of paraffin and oil will silence immediately the noisiest brakes, the expedient is distinctly not recommended.