at Fig. 138, A, and the hinged form depicted at Fig. 138, 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 end on one side,

Fig. 138.-Outlining Common Types of Connecting Rod Big Ends.

this permitting the lower portion to swing down and the crank pin to pass out from between the halves when the retaining bolt is removed. In the marine type, which is the most common, 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 adjustment of the bolts, as while it is important that these should be drawn up as tightly as possible

Fig. 139.-Simple Lapping Tool for Crank Pin and Method of Use. 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 interposed between the top and lower portions 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 outlined at Fig. 138, C and D. In the case shown at C the light edges of the bushings 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 withstand the strains existing and which flatten out quickly, per

Fig. 140.-Adjustable Center Lathe Dog and Crankshaft Supporting Flange for Use in Turning Crank Pins on Lathes.

mitting the bearing to run loose. In the example outlined 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 become 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 reduced 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 scraping, the same instructions given for restoring the contour of the main bearings applying just as well in this case. It is apparent that if the crank pins are not round no amount of scraping will insure a true bearing. A point to observe 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

Fig. 141.-At A, Method of Supporting and Driving Crankshaft for Turning Main Bearings. At B, Showing Use of Crankshaft Supporting Flanges when Machining Crank Pins.

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. Similarly, 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 with a hammer several times after they are tightened up, and the connecting 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 interfered 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 bearing bolts, because these sometimes snap in two pieces and leave the nut slack. The best method of locking is to use wellfitting 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 removable die cast bushings as are used on the more expensive cars. The repairman who is called upon to replace the bearing metal will find the following instructions regarding remetalling bearings of value. The method described was used by the writer while in charge of a large shop where much work of this kind was done and while the instructions given apply specifically to lining the big ends of connecting rods, the same process may be used successfully on any other bearings where the mandrel and collars can be used, the dimensions being changed to suit the requirements of the worker.

In the case mentioned the journals of the crankshaft were two inches in diameter and the big ends of the connecting rods were worn too much to allow of adjusting. A piece of pipe about 9 inches long was procured and turned down in a lathe until it was a shade under 2 inches in diameter, which made a hollow mandrel of it. A piece of steel tubing could have been used to as good advantage had any been available. As the outside of the bearing caps were machined true a couple of set collars were bored out to be a good fit on the mandrel, and while still in the lathe they were recessed out to just fit over the outside of the big ends, as shown in sketch Fig. 4. One of these collars was placed on the hollow mandrel A, after which the mandrel was pushed through the big end, and. the other collar was put on the other side, insuring that the mandrel was as near center as possible for it to be.

The assemblage is then supported on a couple of V-blocks, which are supported on a lathe bed, the ends of the mandrel lying within the V's while the connecting rod hangs between the ways. A piece