Q. How can it be determined just how much nearer?

A. By laying down the segments in full size and proper position in a drawing, and connecting the two centers of gravity by a chord at right angles to the radius or spoke. Where this cuts the center line of the spoke will be the common center of gravity of the two seg

ments.

Q. Suppose that there are three segment-shaped counterweights of the same size, shape and weight, separated by spokes; how can their common center of gravity be found?

A. By laying them down as directed for two segments, connecting the centers of gravity of the two outside ones by a chord at right angles to the spoke radius, and stepping off from this chord, toward the center of gravity of the middle weight, one-third the distance between the chord and that weight. The point thus found will be the common center of gravity of the three counterweights. Q. Is the counterbalance always of iron?

A. No; some builders put in lead counterbalancing for heavy engines.

Q. Are all engines counterbalanced?

A. No; some which have long wheel base and four cylinders are left without counterbalance.

Q. How is the weight for driving-wheel counterbalance, where there are no side rods, calculated?

A. Weigh (1) piston and rod, (2) crosshead and wrist pin, (3) small end of connecting rod; take 2/3 of their

This is the approximate weight to be hung to each crank pin. This being done, the wheel pair is to be placed with axle in a level position and journals resting on smooth flat level strips. If with the calculated weights hung to the pins the wheels hold equally well any crank position given them, the "standing balance" is right; if not, the weights can be decreased or increased until the desired weight is attained.

Q. How do you get the weight of the small end of the rod?

A. By slinging it in a level position, by rope passed through the pin holes, the big end being hung to a fixed point, and the small end to a steelyard.

Q. If the tires are already on, where will the point of suspension be?

A. Outside the tire.

Q. What is the rule for back wheels?

A. The same as for main drivers, omitting to use the weight of the back end of the main rod.

Q. In the case of a consolidated engine?

A. Weigh (1) the big end of the main rod, (2) each end of each coupling rod as explained for the main rod. Divide 2/3 the sum of the weights as mentioned in the foregoing answer for single driver engines by the number of drivers on one side; to this quotient add, for each wheel, the weight of the side rod or side rods connected thereto. Thus:

600 4 150 pounds per wheel; call this A.

Q. In figuring the centrifugal force of a driver counterweight, from where is the radius reckoned?

A. From its center of gravity.

Q. How is this determined?

A. By taking a templet exactly the shape of the weight, hanging it freely from two points from which a plumbline is let fall; where the trace of the lines cross is the center of gravity, no matter how irregular the shape of the body, so long as it is of even thickness and uniform density.

Q. Where there are two counterweights with a spoke between?

A. Find the center of gravity of each, when in place, and connect the two by a line; where this cuts the centre line of the spoke is the common center of gravity.

Q. Where there are three?

A. Find the center of gravity of one; draw an arc (with the center of revolution as a center), through this and the others' centers of gravity; connect the outer ones by a chord, and draw a radius through the center of the middle weight. Mark where this radius, one-third of the distance from the chord to the arc, cuts the radius; there is the common center of gravity of all three weights.

Q. When there are four counterweights?

A. Draw an arc through all four centers of gravity. Connect those of the two adjacent weights by a chord; the same with the centers of the outside weights. Bisect that part of the center line of the spoke between the two chords; there is the common center of gravity.

Q. What is the rule for the weight of the counterbalance on each side?

A. From the weight of the reciprocating parts on one side (including the front end of the main rod), subtract 1/400 the total weight of the engine. Divide the remainder by the number of driving axles; for each wheel add to the quotient the weight of the revolving parts.

Q. At what distance from the wheel center should the center of gravity of this counterweight come?

A. In the same center as the crank pin center.

Q. How is the weight of the reciprocating parts found? A. Add the weights of piston (complete), piston rod, crosshead (complete,) and front main rod end (complete).

Q. How do you get the weight of each end of the main rod?

A. Balance one end on a knife edge at the pin center and let the other end bear (through knife edges) on a platform scale. Having got that weight, reverse the ends to get the other.

CHAPTER LXIII

JOURNALS AND BEARINGS

Q. What name is given to those parts of the axle which bear against the brasses?

A. The journals; this being the common name for the bearing portion of a rotating piece.

Q. What character of bearing do these journals have? A. Usually brasses with semicircular bearing surfaces, and held in cast-iron or cast-steel journal boxes which have also, below the axle, an oil box or cellar, held up to the axle by two bolts. These journal boxes slide vertically in the pedestals or horn pieces, so that the entire engine may rise and fall with rapid running, without the wheels being raised from the track.

Q. What are the two principal classes of driving brasses used?

A. (1) Octagonal, (2) cylindrical.

Q. What are the objections to octagonal brasses?

A. They are more difficult to fit than the cylindrical, and more liable to close on the axle.

Q. What is the disadvantage of babbitting brasses? A. The dust gets into the babbitt and cuts the axle; so that what would be very good practice where dust was not liable to get in, would be bad usage here.

Q. What is the most common usage as regards material for bearings?

A. Soft metal for engine and tender journals, and babbitted strips in rod and driving-box brasses. Soft metal cannot be relied on under all circumstances, as in case of a hot journal the metal or bearing is apt to crush or break in pieces.

Q. What is the advantage of a cast-steel driving box with a bronze shell or lining?