The crank boss may be made out of a brass disc 2-3/4 inches diameter and
3/16 inch thick, from which two curved pieces are cut to reduce the crank
to the shape shown in Fig. 53. The heavier portion, on the side of the
shaft away from the crank pin, helps to counterbalance the weight of the
connecting and piston rods. In Fig. 54 (plan of engine) you will see that
extra weight in this part has been obtained by fixing a piece of suitably
curved metal to the back of the boss.
The mounting of the crank boss on the shaft and the insertion of the crank
pin into the boss might well be entrusted to an expert mechanic, as
absolute "squareness" is essential for satisfactory working. Screw-thread
attachments should be used, and the crankshaft should project
sufficiently to allow room for a flat lock nut. The crank pin will be
rendered immovable by a small lock screw penetrating the boss edgeways and
engaging with a nick in the pin.
Fixing the Standards and Bearings.--Place the two bearings in their
standards and slip the crank shaft through them. Place standards on the
bed, with their centre lines on the crank-shaft centre line.
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