OCR Text |
Show , AutmwoSik Simplified placed between the rubbing parts. These devices are called "bearings" or ' ' bushings. ' ' 'Parts can move on one another in three ways- Namely, they can move in a straight line one on the other, as, for example, the pistons in the cylinders; one can revolve in 'or about the other, as the crank shaft in its supports, or as the wheels on their axles; and the end of a shaft can revolve against a support. sup-port. . In the automobile "where the parts simply slide back and forth, as first given, the pressures and, therefore, wear, if they are well lubricated, are comparatively small, and so, as a rule, no special bearing, is used. By far the greatest amount of moving mov-ing parts move as given iu the second ' AUTO LESSON NO. 110. Bearings. . There are innumerable parts of the aBtoniobile which rub of revolve on other partu, such as tho crank shaft on its supports, tho crank pins in the ends 1 . of the connecting rods, the wheels on their axles. As these parts rub on one anOther; there will bo wear and the generation, of heat;' or in other words, "friction.". Friction cannot be eliminated, but it ean be greatly reduced by lubrication, . .... - and by making th,e rubbing surfaces of materials whose tendency to wear and heat is low, or as engineers' would say, whose ''co-efficient of friction" is low. Lead and bronze are such materials, the former being the better, but, because of its softness, it is mixed with other metals, met-als, such as tin, antimony aud copper, in which case it is known as "white" or "babbitt." metal. To overcome the friction, therefore, some device, such as the properly shaped piece of btibbitt or bronze, or a set of rollers or rolling balls, is usually case; that is, a shaft revolves in another anoth-er part, or a wheel or similar part revolves re-volves about a stationary shaft. Where the shaft is small in diameter, and , this is not done the oil will not be abl( to get to the entire bearing, but wil lubricate only a thin line, one of 'the thickness of the oil hole. done the bearings when tightened will tend to bend tho shaft. In Figure 3, 1 have shown tho middle bearing out of line with the end bearings. O&viously, 'when the caps are tightened tho shaft will be bent. It is for this reason that the novice . should not attempt to fit the main bearings, as it takes skill and experience to do this properly. In fitting the main bearings tho half-time half-time gears should first be studied to Bee if they should be brought, closer together to-gether or'farthor apart. Failure to do this will mean a "growl" of the gears. Unfortunately few mechanics do this, and often by taking too much from the fixed halif of tho bearing will bring the gears too closo together. j "When bearings of this stylo become I worn, the resulting play can bo taken ! out by removiug or filing ou the "Shims," which are shown as B in Figure Fig-ure 2. U'hese are separators made up of a bundle of very thin leaves of brass or of one heavy piece. When of the former, the play is taken up by removing remov-ing one of the leaves, while if the latter, lat-ter, a little is filed off it. Adjusting of the engine bearings should be done by experienced mechanics only, as the bearing must fit the shaft snugly, yet not bind, while the nuts of tho bolts which hold the two halves of the bearing bear-ing together must bo as tight as they can be, without breaking. When much play must be taken out of the bearings, or wheu new bearings aro put in, they will have to be "scraped in." This is done by smearing smear-ing some prussian blue on the shaft and then revolving it in its bearings. The prussian blue will thus mark the high spots of the bearings, which high spotB must then be scraped off, and the process proc-ess repeated, timo and time again, until un-til practically the entire surface of the bearing touches the shaft. In fitting or scraping in bearings, care must be taken. to have the shafts, etc., in lino- Thus wheu the main bearings bear-ings of a crank shaft aro fitted the first half of tho bearings must be first scraped in, and tests made repeatedly to see that no bearing is lower or higher than the others. If this is not the movement little, the bearing is generally nothing but a "sleeve or cylinder made of some auti-f riction metal, as bronze or babbitt, and is called a "bushing"; as. for example, the wrist-pin bushings and universal-joint universal-joint bushing. Where the shaft is of any size and where the movement is fast and the pressure comparatively great, the bearing is called a "journal bearing." In the engine, the journal bearings are almost always made in two parts, for the sake of easy removal, and are made of bronze or of babbitt. The babbitt or bronze bearings have a very low friction, but by the use of ball or roller bearings the friction and wear can bo still further reduced, as when they are used, there is practically no rubbing, as the balls or rollers simply sim-ply roll between the two aiirfaces. "Either ball or roller bearings are used in practically all places other than the engine. Whore tho movement is as given in : the third case; namely, when the end of a shaft or a flange fastened to the shaft revolves or spins on a flat surface, sur-face, the bearing is said to be subjected to a thrust and the bearing is called a "thrust bearing.". Thus the bearing which is placed between the clutch throwout, or shift collar and its fork, is a thrust bearing. Figure 1 shows one-half of a babbitt or bronze bearing. Note the oil grooves A. It is important thnt these be hept cleanly cut and unobstructed, as if |