gines the Babbitt metal is often poured directly into the connecting rod lower end and the connecting rod cap. On high priced motors the alloy is made in the form of die cast bushings, one of which fits the connecting rod and the other the cap. Bronze brasses are also used sometimes. (See Fig. 47.)

Q. What means are provided to adjust bearings?

A. A number of shims or liners of thin metal, such as sheet copper or brass stock, ranging from .002" to .006" and sometimes thicker, are interposed between the upper and lower connecting rod

Fig. 49.-How Chalmers Pistons and Connecting Rods Are Weighed and Balanced So that Members Working in Unison Will Have the Same Weight and Assure Smooth Running of Motor.

members. After a certain amount of service, if the brasses, as the bushings are technically termed, wear so that there is appreciable looseness between the connecting rod and crank pins, one or more of these shims may be removed and the boxes brought closer together to compensate for the amount of wear. Sometimes one thick shim of fiber or brass is provided instead of the greater number of smaller ones, and this is thinned down by filing to decrease the distance between the brasses.

Q. Are plain bearings the only practical kind?

A. While plain bushings are more generally used on the connecting rod big ends and main journals of the crankshaft, anti-friction bearings of the ball or roller type have been used with some degree of success.

Q. What are the advantages of anti-friction bearings?

A. Anti-friction bearings, especially those of the ball type, turn much more easily than plain bushings and less power is consumed by bearing friction when they are employed. They are also more enduring than the plain journals, and when properly selected show absolutely no wear after extended periods of operation. (Fig. 50.)

Q. What is the accepted relation between cylinder bore and piston stroke?

A. The piston stroke of modern engines is longer than the diameter of the bore. Usually the piston movement is equal to about 1.25 times the diameter of the piston. The piston stroke in extreme cases may be 1.75 or 2 times the cylinder bore.

Q. What is a long stroke motor?

A. Any motor where the ratio of stroke to bore is greater than 1.5 to 1 is termed a "long stroke motor."

Q. What limits length of stroke?

A. The permissible length of stroke of the piston is limited by an arbitrary piston speed which it is not desirable to exceed because difficulties in lubrication and cooling are apparent at greater piston speeds than that established by common practice.

Q. Define "piston speed" and give commonly accepted limits. A. The stroke of the piston in inches multiplied by 2 and this product multiplied by the number of revolutions per minute and this in turn divided by 12 will give the piston speed in feet per minute. An engine with a six inch stroke going at 1,000 R. P. M. will have a piston speed of 1000 feet per minute, which is the commonly accepted limit.

Q. Of two engines going at the same crankshaft speed will

the long stroke or short stroke engine have the highest piston

speed?

A. The piston of the long stroke motor will obviously have the greatest piston speed. The shorter the stroke of an engine, the greater the number of revolutions its crankshaft can attain.

Q. What is the crankshaft?

A. The crankshaft is the part of the motor which converts the reciprocating motion of the piston to a continuous rotary movement suitable for driving the wheels of the automobile.

Fig. 50.-Showing Ball-Bearing Crankshaft of the Two-Bearing FourThrow Type used in White Motors.

Q. What are crankshafts made of?

A. Crankshafts are invariably made of steel and are usually formed by the drop forging process which forges them out approximately to the correct form. Crankshafts employed on moderate priced engines are usually of carbon steel, while those utilized on high powered engines are made of chrome-nickel and other high tensile strength alloy steels.

Q. What is the relation between crankshaft throw and piston stroke?

A. The crankshaft throw, which is the distance between the center line of the crank pin and that of the crankshaft proper, is always half the piston stroke.

Q. Do all crankshafts have the same number of throws?

A. Crankshafts intended for multiple cylinder engines have more throws than simple forms intended for one or two cylinder engines.

Q. Are crankshafts always in one piece?

A. Crankshafts are not always made from one forging or piece of metal. They are sometimes composed of a number of distinct machined pieces fastened together by mechanical means. (Fig. 51.) Q. Why are built-up crankshafts necessary?

A. On small single cylinder and two cylinder V engines, such as used for motorcycle propulsion, the connecting rod is usually formed

in one piece and the crankshaft assembly must be completed after the connecting rod is in place on the crank pin. With a split connecting rod construction one piece crankshafts are employed, whereas when one-piece connecting rods are used it is necessary to use a built-up crankshaft.

Q. What are counter weights?

A. Counter weights are fan shaped masses of cast iron attached to the crankshaft of single cylinder and some forms of two cylinder motors to balance the reciprocating weight of the pistons and a part of the connecting rods. (Fig. 52 A.)

Q. How are they attached to the crankshaft?

A. The conventional method of attaching counter weights is to bolt them to the crankshaft webs, though on built-up crankshafts used on motor cycle engines they are sometimes cast or forged integral with the flywheel members that correspond to the webs of the usual crankshaft and to which the crank pin is attached.

A

B

C

Fig. 52. Showing Various Forms of One and Two Cylinder Crankshafts. A-Single Throw Crankshaft With Balance Weights. B-One-Throw Two-Cylinder Crankshaft With Balance Weights. C-Crankshaft for Two-Cylinder Opposed Motor.

Q. How are crankpins spaced in two cylinder engines?

A. Crank pins of two cylinder engines may be arranged in two different ways. In vertical engines both connecting rods may be attached to a common crank pin, as shown at Fig. 52 B, or they may be placed at 180 degrees or opposite each other, as shown at Fig. 52 C