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Cuddio Rhestr Erthyglau

14 erthygl ar y dudalen hon



CYCLECAR AND MOTOR CYCLE I NOTES. [By CELERITER. ] I MOTOR CYCLE ENGINE LUBRICATION. SEMI-AUTOMATIC VERSUS AUTO- MATIC SYSTEMS. The subject of lubrication is a very large one, and one which is still receiving a great deal of attention from engine designers, both of car and motor cycle engines, and is likely to receive attention for a long time. Lubrication in the eatly days of motoring was a more or less crude process, not nearly so thorough as to-day, though even yet there is a very wide field for improvement in many makes of machines, and it would hardly be correct to say that lubrication is perfect in even the very beat makes. To take the case of the motor cycle first. The motor cyclist of to-day has far less need to trouble about the lubrication of his engine than his brother motor cyclist of only a few years ago. I do not think it would be very incorrect to say that by far the greater majority of motor cycles have semi-auto- matic drip feed lubrication. Oil is fed into the crank-case by means of a pump, which in the first place is hand-operated, that is to say, a charge of oil is either sucked or forced into the pump barrel by hand, and afterwards a spring feeds the oil from the barrel into a pipe, from which the oil drifts visibly into a second pipe, which conveys it into the engine crank case. The flow of oil into the crank case can be regulated by means of a needle valve. This system is sure and simple so far as getting the oil into the crank case is concerned. It has, however, one or two disadvantages, which, though they are decidedly disadvantages, can hardly be called defects. In the first place it is necessary to keep on depressing or racing the pump-plunger, as each pump- ful of oil finds its way into the crank-case. It is also necessary to continually alter the setting of the needle valve, according to the temperature conditions of the atmosphere; the colder the day, the wider open the valve must be, and vice versa. It must also be adjusted to suit different brands of oil. In the bands of the novice this necessity for fine adjustments may lead to either over or under lubrication of the engine. Over lubrication is not a very serious item, as its chief evil is the sooting up of the plug or plugs and carbonisation of the cylinders and piston plugs. On the other hand, under lubrication is a serious matter, though the engine tnay not be sufficiently starved of oil to absolutely seize up, it may be sufficiently short of oil to allow the various moving parts to come into contact with the station- ary parts, and cause very rapid wear, which will in the end lead to loss of power and noisy running, and perhaps often a break- down, for the oil is in the crank case in order to work between the moving and stationary surfaces and prevent their coming into con- tact with each other. With the semi-automatic drip-feed lubrica- tor generally in use, it is quite possible to forget to turn the oil on, and it usually must be turned off at the end of a run, or the oil will syphon into the crank-case and give no end of trouble when the engine has to be started up again or it is possible to give too little oil by forgetting to adjust the needle valve to suit the conditions of run- ning, which, of course, vary accord- ing to the speed at which the engine is revolving, or the load it has to carry, which varies on altering gradients or when ridden with sidecar attached or solo. It is necessary therefore in order to obtain the best results with a semi-automatic drip feed lubricator to keep a watchful eye on the drip of oil. In order to make quite sure that one is giving the engine sufficient oil it is well at times to open the needle valve wide and push a pumpful of oil straight into the crank case, then if smoke comes from the exhaust it is a sign that the engine is sufficiently lubricated if several pumpfuls of oil have to be injected before the smoke issues, it shows the engine is being under lubricated, and the needle valve should be readjusted to give a rather faster drip. This seems a crude method of having to ascertain whether the engine is sufficiently lubricated, and indeed so it is, but the only other way would be to empty the crankcase at the end of each run and ascertain whether there is sufficient oil left in it, and this is a rather tiresome process. Some makers used to fit a small inspection gauge at the bottom of the crank- case, and though I believe that this is only being done by very few makers nowadays, I see no reason why the idea should not be elaborated on and again brought into general practice. An improvement on the semi-automatic drip feed is the duplex feed now being standarised on some makes, that is a system whereby the oil is sucked into the engine crankcase by means of the vacuum created in the crankcase w hen non-return ball valves are fitted. This system is quite good in theory, but not so good in practice. In the first place the oil is fed from a small pipe from the oil tank, whence it falls into a sight feed dome and then feeds into the crankcase, the flow can be regulated by a needle valve as in the semi-automatic type. but the trouble with this system is that the oil in falling generally gets splashed back into the glass sight dome and obscures the flow so that it is difficult to tell exactly how much oil is going into the engine. Then again, the flow varies with a given opening of the needle valve, according to the temperature of the air and the thickness of the oil. In order to supplement the automatic flow a hand pump is fitted, so that lubrication can be effectively maintained, but this half of the affair is a return to the earlier days, though at the same time quite useful if not actually necessary. This system is a slight advance on the semi-automatic type, for pro- viding the oil is not turned off altogether the engine will feed itself a certain supply of oil even if the rider forgets to regulate the flow or pump oil in. Some makers are fitting pump lubrication to motor cycle engines; this is following car practice as regards the pump. Oil is pumped out of a sump into the crankcase and fed by pipes into the main bearings and into the piston through a hole or holes in the cylinder walls. This system is quite automatic and has much to commend it, inasmuch as it would be difficult to under-lubricate the engine or to forget to lubricate, as is possible with either of the above systems. There are, however, one or two draw backs. In the first place there is the possibility of the pump going wrong, and as it is difficult to fit an oil indicator such as is fitted to cars to show that oil is actually flowing, there is just a possibility that the engine might be starved and seriously damaged before the lack of oil was discovered. Then again this system uses the same oil over and over again, and each time the oil passes through the pump and bearings it looses some of its viscosity or lubricating qualities, and is never as fresh as the oil which is continually dripping in from a tank to make up loss. Then again pump lubrication adds somewhat to the complica- tion of the machine and to the cost of manufacture so that unless some really simple form of pump is devised which will adapt itself to motor cycle work it is hardly likely that pump lubrication will become universal at present at any rate. New riders must therefore pay proper attention to the oiling of their engines and endeavour to find out as soon as possible bow to regulate the supply to their engines to get the best results with the conditions under which they are riding. There is no fixed standard for set- ting the feed of a drip type lubricator, but there is one golden rule—i.e. give the engine plenty of oil rather than too little. Oil is cheaper than new bearings, and even if it does aoot up the plugs or carbonise the inside of the engine, never mind. The revival of the twin cylinder engine for lightweight and medium weight machines has revived the old problem of equal lubrica- tion of the front cylinder, and so far as I am aware the solving of the problem seems to be as far off as ever. Some makers rely on feeding the oil in bulk into th< crank case, and then putting a baffleplate over the back cylinder base and leaving the base of the front cylinder as wide open as possible, the object being to prevent the connecting rod and crankshaft from splashing all the oil into the back cylinder and leaving the front one starved. Those who have adopted this system have met with some measure of success, but it is only necessary to enquire into the lubrication systems of the twin cylinder machines in the T.T. races, to find how much reliance makers placed cn this system, for in almost every instance a separate supply of oil was led to the front cylinder. I think this system might be modified by leading all the oil into the engine via the front cylinder twin pipes might be led into the front and back sides of the front cylinder walls and this would ensure the front piston being properly lubricated, whilst the rest of the engine would be lubricated by splash in the ordinary way. I have not heard of this system being tried, but I see no reason why it should not be tried and with a little research and careful calibration quite good results should be obtained. The usual semi-automatic drip feed lubrication could be used and an auxiliary pump might be fitted to feed oil direct into the crankcase if required. Possibly this system might lead to complica- tions in the hands of a careless rider, but to the great majority and especially to the speed merchant, it would be a great boon. Lubrication systems have a long way to go before they are perfect. Car lubrication is another matter, and as I find I have already written enough on the subject of motor cycle engine lubrication, this will have to remain over until another time.













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