The last part of the pusher control is the pusher itself. It is simply a round brass rod ¼ inch in diameter and ¾ inch long, with a hole drilled through it lengthwise and threaded to fit the spindle. Solder a bit of brass near one end, to make it heavier on one side than on the other.
Now, when the motor is set in place in the hull and its small pulley is belted to the large pulley on the spindle and the current is turned on, the spindle revolves, but the weight on the pusher will keep it from turning with the spindle. Instead, the curious result is that it screws itself toward the free end of the spindle, and when it reaches the end, the hollow pusher goes over the stem of the piston. When it strikes the piston it pushes on it until it presses the other end of the stem against the pin of the bicycle valve and this opens it.
If you will keep the piston, the pusher, and the bearings well lubricated with sewing-machine oil, there will be little power lost through undue friction. But you must be careful not to get any oil on the commutator of the motor, for this will keep it from running properly.
The Propeller-Shaft.—Before you install the motor you must put the propeller-shaft through its bearing in the tail block.
To make the propeller-shaft, get a piece of soft steel rod ⅛ inch in diameter and 5¼ inches long and thread it at both ends. Slip it through the tube which forms the bearing. Soak some cotton-waste in machine oil and pack it in the stuffing box in the tail block. Now screw the circular plate to the face of the tail block to keep the packing in place.
Installing the Motor.—While we have given you the height to make the pillow block, it will, of course, depend on (1) the height of the motor, and (2) the height of the center of the piston when both are measured from the floor of the hull; this is because the pusher spindle and the piston stem must be exactly in a line with each other.
Another thing: The motor we have shown is 3 inches high from its base to the center of its armature shaft; but the motor you get may not be of this height. While it can’t be any higher than 3 inches unless you change the design of the boat, it can be shorter if you mount it on a block of the right thickness.
Before installing the motor in the boat, see that both pulleys are in a line with each other, and put on a belt. Thread the end of the motor-shaft and fit a coupling to it so that the propeller-shaft can be screwed into the other end. To make the coupling take a piece of brass rod ¼ inch in diameter, 5/16 inch long; drill a 3/32-inch hole in it, and thread it to fit the motor- and propeller-shafts.
Screw the coupling on the motor-shaft. Mount the motor on a board of the right thickness, and set it in position in the hull. Screw the propeller-shaft into the coupling, and be sure to have the motor set so that the shafts are in perfect alignment—that is, in a line with each other—as shown in [Fig. 15].