CAISE OF ENGINE WEAR

New Zealand Times, Volume LII, Issue 12211, 8 August 1925, Page 18

CAISE OF ENGINE WEAR

ENTRANCE OF ROAD GRIT RESPONSIBLE FOR CARBON. Owing to the tremendous number of cars in use in America by all classes of the population, automobile engineers in that country find it necessary to cater particularly for tho owner who cannot or will not take any interest in the mechanical condition of the engine or chassis. That type of ownoi wants the car to be capable of taking him anywhere at any time, preferably on top gear all the way, and does not wish to spend even a few hours every week in the process of oiling, greasing, and adjustment. Consequently, American engineers are busy developing reaps whereby the engine may be irade to run for phenomenal mileages without wear and without replenishment of bil. In this country the average owner ia far more interested in the mechanical side, and does endeavour to take care of his-car, but. nevertheless any invention which lessens the labours of maintenance. apd makes the power unit more durable is certainly welcome. The dual -problem is being tackled by the development of the air cleaner and what is known aa the oil rectifier. EXCLUSION OF GRIT Before describing those devices ic will be as well to consider the causes of engine wear and the reason for tho gradual deterioration of the oil in the sump. Two main factors are responsible for both occurrences, namely, road grit- entering the carburetter with the eir, and fuel which gets past the pistols and mixes with the oil. Experiments have shown that, while the dilution of oil by the fuel is sufficiently serious in itself, the bad effects are accentuated when a great amount of road grit is entering the engine past the inlet valves. Consequently, if n is possible both to exclude the gr.'t and prevent dilution, then greater duration Will be obtained and' at the same time oil replenishment will be necessary only after a considerable mileage. - . . , • . The exclusion of gilt is shown to, re-duce-the amount of carbon deposited on the cylinders and pistons. Many years ago Dr W. R. Ormandy, the wellknown -petroleum expert, showed by analysis that a great proportion of the carbon ia in reality composed' of road grit. That fact seems to 'have been rediscovered recently, and is a good ar-gument-in favour of the air cleaner. It will‘therefore be seen that.if we can exclude dust and grit and,, prevent deterioration of the oil there is really no reason why an engine should not be capable of running- 10,000 to 12,000 miles without decarbonise tion or oil replenishment.; Furthermore, there i« no doubt that when an air cleaner is fitted , the fife of tho valves and valve guides is greatly prolonged. ResearcEls have shown that the rate at which petrol will get past the pistons and mix with the oil largely depends upon the temperature at which the engine is running. Thus, in recent tests, the oil was found to become diluted to the extent of 2 per cent, with the engine running at 17b deg. F. in the course of a short run. Under exactly the same conditions, but with -a temperature of 59deg. F. the dilution was 5 per cent. Incidentally, ‘ls per cent, may be, taken as the danger point of oil dilution, because, if the proportion of fuel exceeds that figure, the lubricating properties will be adversely affected. . Bearing these facts in mind, the owner-driver can reduce the extent of dilution by using care in running the engine, particularly when starting on a cold morning. If an air-strangler is fitted to the carburetter it should he used sparingly, because the overrich mixture produced will tend to become. deposited upon tho cold cylinder walls; with the result that petrol will get past the pistons. Similarly it is a mistake to inject more lEa n a small quantity of fuel into the cylinders. FILTERS FOR OIL ! AS regards engine oiling systems, it has; of course, long been recognised that'vefficient , filters are necessary through which the.oil must be circulated while sucli .filters are more or less effective in removing particles of dirt or carbon which become mixed with the oil;'they will obviously be incapable of affecting the extent to which the oil is diluted with' fuel; The only way of eliminating the- fuel from the oil consists in the application of heat, which will drive off the 'spirit in the form of gas. Several different types of heater are being evolved for the purpose, and the whole matter is really in an experimental stage, so that it will be best, perhaps, to confine our description to tlje principles involved m anv of the processes. Two pumps are used- One draws oil from, the sump and delivers it to the rectifier, which consists of;a small reservoir heated by a coil of piping" through which exhaust gases pass. It is here that any fuel which has become mixed with the oil is driven off. Incidentally, as .the oil comes straight from the engine, it will already -be fairly hot, so that the amount of additional heating required is small. The oil then passes on to a second reservoir, in which it is stored and cooled before being returned to the engine. Provided that the capacity is adequate there is no need to employ any special cooling device before ribbing the outside of the casing. A second pump draws the cool, clean oil from the reservoir and delivers it to all the engine hearings, whence, after being used, it drains hack to the sump and goes' through the whole process ovei again. -The lav-out is in many respects similar to the dry-sump lubrication system used in racing and aircraft enejnes, with the addition of a rectifier to remove fuel from the oil. The increased cost and complexity involved in fitting an air-cleaner and oil rectifier "to an engine as standardised components might he urged as a disadvantage, hut if their use will euahle the owner to save considerable time and money, owing to toss frequent replenishment. repairs, and replacements. the additional expenditure will simelv he Not only will the rate of wca? «f the cylinders bode

creased, but the life of the crankshaft and bearings will also be prolonged. Then, again, the majority of modern power units are fitted with an oil pump which delivers the lubricant through small-bore piping and passages. A tremendous amount of damage can he done to the engine if it is run at full throttle with a partiallv defective oiling system and trouble of this kind is usunllv due tn the oilwnvs hemming choked by nnrticles of grit. The use of an air clenner will undoubtedly tend tn reduce the ’ikclihood of that form of engine trouble.