138
end on one side, this permitting the lower portion to swing down the crank pin to pass out from between the halves when the retaining bolt is removed. In the marine type, which is the most com- mon, one or two bolts are employed at each side and the cap must be removed entirely before the bearing can be taken off of the crank pin. The tightness of the brasses around the crank pin can never be determined solely by the ad- justment of the bolts, as while it is im- portant that these should be drawn up as tightly as possible the bearing should fit the shaft without undue binding, even if the brasses must be scraped to insure a proper fit. As is true of the main bearings, the marine form of connecting rod has a number of liners or shims in- terposed between the top and lower por- tions of the rod end and these may be reduced in number when necessary to bring the brasses closer together.
In fitting new brasses there are two conditions to be avoided, these being out- lined at Fig. i6, C and D. In the case shown at C the Hght edges of the brush- ings are in contact, but the connecting rod and its cap do not meet. When the retaining nuts are tightened the entire strain is taken on the comparatively small area of the edges of the bushings which are not strong enough to with- stand the strains existing and which flatten out quickly, permitting the bear- ing to run loose. In the example out- lined at D the edges of the brasses do not touch when the connecting rod cap is drawn in place. This is not good practice, because the brasses soon be- come loose in their retaining member. In the case outlined it is necessary to file off the faces of the rod and cap until these meet, and to insure contact of the edges of the brasses as well. In event of the brasses coming together before the cap and rod make contact, as shown at C, the bearing halves should be re- duced at the edges until both the caps and brasses meet against the surfaces of the liners as shown at A.
Before assembling on the shaft, it is necessary to fit the bearings by scrap- ing, the same instructions given for re- storing the contour of the main bear- ings applying just as well in this case. It is apparent that if the crank pins are
��Popular Science Monthly
not round no amount of scraping will insure a true bearing. A point to ob- serve is to make sure that the heads of the bolts are imbedded solidly in their proper position and that they are not raised by any burrs or particles of dirt under the head which will flatten out after the engine has been run for a time and allow the bolts to slack off. Simi- larly, care should be taken that there is no foreign matter under the brasses and the box in which they seat. To guard against this the bolts should be struck wuth a hammer several times after they are tightened up, and the con- necting rod can be hit sharply several times under the cap with a wooden mallet or lead hammer. It is important to pin the brasses in place to prevent movement, as lubrication may be inter- fered with if the bushing turns round and breaks the correct register between the oil hole in the cap and brasses.
Care should be taken in screwing on the retaining nuts to insure that they will remain in place and not slack off. Spring washers should not be used on either connecting rod ends or main bear- ing bolts, because these sometimes snap in two pieces and leave the nut slack. The best method of locking is to use well-fitting split pins and castellated nuts. In a number of the cheaper cars, the bearing metal is cast in place in the connecting rod lower end and in main bearings, and is not in the form of re- movable die cast bushings.
Precautions in Reassembling Parts When all of the essential components of a power plant have been carefully looked over and cleaned and all defects eliminated, either by adjustment or re- placement of w^orn portions, the motor should be reassembled, taking care to have the parts occupy just the same relative positions they did before the motor was dismantled.
Before the cylinders are replaced on the engine base, heavy brown paper gas- kets should be made to place between the cylinder base flange and top portion of the engine crank case. Gaskets will hold better if coated with shellac, as it fills irreg-ularities in the joint and assists materially in preventing leakage after the coating has a chance to set.
�� �
