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Show ; FUNCTION AND IIMTANCE OE MPISpiHG Professional Advice on the Mechanism of Automobile Engine; Compression Problems Explained. Among the subsidiary parts of the mechanism of the automobile engine, none is more important or exerts a greater influence on satisfactory operation oper-ation than the pistons and piston rings. Car owners generally do not realize this, but as a matter Qf fact, it is only within very recent years that the designers de-signers and engineers have begun to understand the importance of the matter, mat-ter, so the owner need not blush at his excusable ignorance. The work of the pistons is not by any means a sinecure. To begin with, the pistons receive the force of the impact of the exploding gases on the power stroke and this pressure often reaches 400 pounds per square inch of piston head area. Next the piston descends de-scends on the intake stroke and creates cre-ates a vacuum above it, which is filled by the new charge of explosive gas. And all this must be done in a temperature tem-perature that at times will run as high as 500 degrees F. Obviously, then, the pistons must be made of sturdy material, mate-rial, that will keep its shape under the high temperatures involved. There must not be any appreciable leakage of gas past the pistons, or the power of the engine will be greatly impaired, fuel consumption will be increased and by the same token there will be oil leakage and carbonization of the cylinder cyl-inder afflicted-Inverted afflicted-Inverted Tumbler. A cylinder may be likened to an in-: in-: vrd tumbler, inside which are jitise.H toehold a pin or arm, to which ;'Q: is attached the connecting rod. The V function of the piston demands that it u'ilw. shall travel up and down within the ' vylinder. This means that it must be ijljc just a. tiny bit smaller than the insiSo of the cylinder, moreover, the tendency of all metal to expand when heated, places very definite limitations to the tightness of the piston's fit. But, there must not be so much space between cylinder and piston that the explosive gas can leak downward, and the lubricating oil force its way up from below. To obviate these possibilities, possi-bilities, tho piston is made with a number num-ber of grooves, two, threo or even four. Tn theso grooves flexible rings, having a certain amount of spring, are fitted. These rings stick out .iust a little beyond be-yond tbe surface of the piston, cling to the cylinder wall and consequently keop in the gas and prevent the oil from making its way into the combustion com-bustion chamber. From the beginning of the automobile automo-bile age until today many different materials have been experimented with in the attempt to find the best piston material. At the present time enst-iron is the prevailing material, but aluminum is making rapid strides into popular favor. Aluminum has the great advantage of lightness, which is more essential hore than in any other part of the ongine, because at this point the greatest burden of inertia must bo overcome. In the beginning, there was a great deal of trouble with tho use of aluminum pistons. The designers de-signers have discovered that if ribs arc provided, the heat may be conducted conduct-ed away from the piston head and this lighter metal will stand up as well ;ih heavior cast iron. The elimination of a part of tho heating propensity also reduces carbonization. Aluminum Pistons. It was found that with aluminum pis-. pis-. Jons there was likely to be a certain jiount of so-called slapping before thiXiotor warms up. This was duo to the fact that owing to the much greater coefficient of expansion in aluminum, it was necessary to allow greater clearances. Therefore, until tlic metal became heated and expanded, expand-ed, a certain amount of slapping was inevitable. This slapping is not noticed no-ticed in present installations. If the water in tho cooling system should get low, excessive heating will quickly develop de-velop in the aluminum type. Further, if tho composition of these pistons is not. right, trouble will ensue speedily, but today thorp is little to be feared on this score, because the manufacturers manufactur-ers have well learned their lessons in composition and design. In cases where aluminum pistons are not desired or canuot be fitted, it is possible to get a fair degree of lightness light-ness by drilling tKe ordinary east-iron pistons. Drilling the piston must be carried out not only with skill, but with a full understanding of just what the requirements of the case arc. It is common practice to drill the ordinary piston in two or three places to secure drainage of an excess of oil, which has been getting into the combustion 'hainher. Frequently the lower piston ring groove will be bored with a number num-ber of small holes to permit draining. drain-ing. The practice of fitting a wiper ring in the lower groove to remove excess oil from tiie cylinder wall and R distribute it evenly, is often resorted f to. In cases where the pistons are I not provided with oil grooves, these can be cut and will usuallv help in cases where there has been habitual 'rouble with the lubrication of ther cylinders. Mj ear owners have had trouble 'icaky piston rings, which permit iii excess of oil to work its way into the combustion chamber, which, at the same time, the fuel is passing down in-to in-to the oil reservoir. This produces a double waste, of oil and of gasoline, in addition to impairing tho operating qualities of the car. At the same time, compression is reduced and the power of the engine is materially impaired and water is allowed to collect m the crankcase, mixing with the oil and tending to destroy its lubricating value. Leak Effects. To meet these conditions, there have been placed upon the market within the past couple of years a uumber of patented rings of various types, each one claimed to solve the entire problem at one fell swoop. Some of these special spe-cial rings are good and others are certainly cer-tainly no better than the ordinary split variety. Secondly, the best of them must be properly-fitted to give satisfactory satis-factory results. Therefore, the car owner who buys patent rings, puts them in and considers the job done, may have an unpleasant surprise coming to him. Unless the owner is an expert mechanic, I would advise him to have his new rings fitted by the service station. sta-tion. In the case of Ford owners, it is now possible to get aluminum pistons with patent rings already In place. "Lapping In" Method. In fitting new pistons, it is necessary to have them lapped in, so as to obtain ob-tain a perfect fit. Lapning in is carried car-ried out with a fine abrasive, jeweler's rouge is good, and this material is mixed with oil or kerosene and is rubbed evenly over the surface of the piston. This latter s tnen inserted in the cylinder and worked around until un-til it moves with perfect freedom, after which both parts are thoroughly cleaned. There are concerns in every city and most towns today specializing in the fitting of pistons and in reboring cylinders. cyl-inders. When it is necessary to have a cylinder rebored and new pistons fitted, it is a mistake to have just the one done. The entire cylinder block should be bored and have new pistons. It is vitally important to keen the pistons pis-tons in good shape, if the operation of the engine is to be kept up to the mark. |