Page:Popular Science Monthly Volume 88.djvu/163

 Popular Science Monthly

not always necessary to use guiding strips of metal when replacing rings as it is often possible, by putting the rings on the piston a little askew and man- ceuvering them to pass the grooves with- out springing the ring into them. The top ring should be the last one placed in position.

Before replacing pistons in the cylin- der one should make sure that the slots in the piston rings are spaced equidistant on the piston and if pins are used to keep the ring from turning one should be care- ful to make sure that these pins fit into their holes in the ring and that they are

���Fig. 14. Showing method of sup- porting crankcase to provide ready access to connecting rod and crankshaft bearings

not under the ring at any point. The cylinder should be well oiled before at- tempt is made to install the pistons. The engine should be run with more than the ordinary amount of lubricant for several days after new piston rings have been inserted.

Inspection and Refitting of Enc/ine Bearings

While the engine is dismantled one has an excellent ojiportunity to examine the various bearing points in the engine crankcase to ascertain if any looseness exists due to depreciation of the bearing

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surfaces. As will be evident from the views at Figs. 14 and 15, both main crankshaft bearings and the lower end of the connecting rods may be easily exam- ined for deterioration. With the rods in place as shown at Fig. 14, A, it is not difficult to feel the amount of lost mo- tion by grasping the connecting rod firm- ly with the hand and moving it up and down.

The appearance of the engine base af- ter the connecting rods and flywheel have been removed from the crankshaft is shown at Fig. 15, while the appear- ance of the upper portion of the crank- case, after the crankshaft is removed is clearly shown at Fig. 14, C.

After the connecting rods have been removed and the flywheel taken ofif the crankshaft to permit of ready handling any looseness in the main bearing may be detected by lifting upon either the front or rear end of the crankshaft and ob- serving if there is any lost motion be- tween the shaft journal and the main bearing caps. It is not necessary to take an engine entirely apart to examine the main bearings as in some forms these mav be readily reached by removing a large inspection plate either from the bottom or side of the engine crankcase. The symptoms of worn main bearings are not hard to identify. If an engine knocks when a vehicle is traveling over level roads regardless of speed or spark lever position and the trouble is not due to carbon deposits in the combustion chamber one may reasonably surmise that the main bearings have become loose or that lost motion may exist at the con- necting rod big ends, and possibly at the wrist pins.

Adjusting Main Bearings

When the bearings are not worn enough to require refitting the lost mo- tion can often be eliminated by remov- ing one or more of the thin shims or liners ordinarily used to separate the bearing caps from the seat. Care must be taken that an even number of shims of the same thickness are removed from each side of the journal. If there is con- siderable lost motion after one or two shims have been removed, it will be ad- visable to take out more shims and to

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