Page:Popular Science Monthly Volume 88.djvu/165

 Popular Science Monthly

will generally be distributed somewhat. If the heavy marks which usually appear at first are simply removed by light scraping, these "point bearings" are gen- erally enlarged, but a much longer time will be required to distribute them.

The number of times the bearing must be applied to the journal for testing is important, especially when the box or bearing is large and not easily handled. The time required to distribute the bear- ing marks evenly depends largely upon one's judgment in "reading" these marks. In the early stages of the scraping op- eration, the marks should be used paiitly as a guide for showing the high areas, and instead of merely scraping the marked spot the surface stirrounding it should also be reduced, unless it is evi- dent that the unevenness is local. The idea should be to obtain first a few large but generally distributed marks ; then an evenly and finely spotted surface can be produced quite easily.

In fitting brasses when these are of the removable t\'pe, two methods may be used. The upper half of the engine base may be inverted on a suitable bench or stand and the boxes fitted by placing the crankshaft in position, clamping down one bearing cap at a time and fitting each bearing in succession until they bed equally. From that time on the bear- ings should be fitted at the same time so the shaft will be parallel with the bot- tom of the cylinders. Considerable time and handling of the heavy crank- shaft may be saved if a preliminary fit- ting of the bearing brasses is made by clamping them together with a carpen- ter's wood clamp and leaving the crank- shaft attached to the bench. The brasses are revolved around the crank- shaft journal and are scraped to fit wher- ever high spots are indicated until they assume a finished appearance. The final scraping should be carried on with all bearings in place and revolving the crank- shaft to determine the area of the seat- ing. When the brasses are properly fit- ted they will not! only show a full Ijear- ing surface but the shaft will not turn unduly hard if revolved with the same amount of leverage as afforded by the flywheel rim or starting crank, bearing caps being bedded down and lubricated.

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��A

��Liners Vi^Jl d:^:

��B

��HingedJype Hinge

���Retdining Bolts

��Fig, i6. Outlining common types of connecting rod big ends

Bearings of white metal or babbitt can be fitted tighter than those of bronze and care must be observed in supplying lubricant as considerably more than the usual amount is needed until the bear- ings are run in by several hundred miles of road work. Before the scraping process is started it is well to chisel an oil groove in the bearing as these grooves are very helpful in insuring uni- form distribution of oil over the entire width of bearing and at the same time act as reservoirs to retain a supply of oil. The tool used is a round nosed chisel, the effort being made to cut the grooves of uniform depth and having smooth sides. Care should be taken not to cut the grooves too deeply as this will seriously reduce the strength of the bearing bushing.

Rcmctalliiig and Fitting the Connecting Rods

Fitting and adjusting the rod bear- ings, especially those at the crank pin end, is one of the operations that must be performed several times a season if a car is used to any extent. There are two forms of connecting rods in general use, known respectively as the marine type, shown at Fig. i6, A, and the hinged form depicted at Fig. i6, B. The hinge type is the simplest, but one clamp bolt being used to keep the parts together as the cap is hinged to the rod

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