Crankpin

“ The crank and connecting rod are employed in some machines. If there are two only, they must not be placed in opposite positions, but be fixed at an angle, so that there are times when each rod is under compression, a strain which delicate rods cannot stand. In the three-throw crank, employed in the Matchless tricycle, this objection is obviated, for one, at least, is at all times in such a position as to be in tension. The objection to the crank is the fact that it weakens the shaft, and that it can only be used with a clutch, not with a differential gear. ”

“ The crank shaft is reduced to the very minimum, there being only one crank pin with two main bearings which can, without any difficulty whatever, be kept absolutely in line with each other and thus prevent binding and loss of power. Again, the use of a single-throw crank not only reduces the cost and weight of the crank [p246] itself, but makes it very much less liable to damage; long crank shafts with several crank pins being frequently twisted by improper explosions in the cylinders. ”

“ The Crank is that part of an engine by which the effect of the steam acting against the piston is converted into work. There are two kinds, Side and Center crank. The term Side crank refers to a disc plate or a crank attached to one end of a shaft and in which is placed the crank-pin. When the shaft extends to the right the engine is called a right hand engine, and when it extends to the left it is called a left hand engine. ”

“ Lock the crank to the axle with a 1/2" screw. Adjust the axle and keep it in position with two leather washers locked to the axle just outside the journals. Clamp the block to the base, adjust it in line with the crank, and fasten it with two 1-1/2" screws up thru the base. The last connection to make is between the crank and connecting-rod. To make this, raise the piston to its highest position, and turn the crank to its lowest; choose what seems the best point for the screw, marking the point on crank and connecting-rod; now lower the piston and raise the crank ”

“ When three cranks, 120° apart, are employed, it will be found that the effect of the shortness of the connecting-rods in causing forces to act in the line of the stroke is reduced to a couple tending to tilt the engine in a fore and aft direction, which may in its turn be balanced by using a second set of three cranks on the same shaft, the second set being so arranged that the couple to which it gives rise neutralizes the couple due to the first set. ”

“ A crank-arm would do equally well, and the disc is shown simply as illustrating a different plan. The disc F is fixed on the crank-shaft either by screwing, by a transverse pin, or by a key.
Fig. 1.
Fig. 2.
The crank-shaft is 1⁄4 in. steel, and should be turned smooth and parallel to fit the hole in the standard. This hole should also be smooth and parallel, which it will be if properly bored with a suitable tool. A long bearing has no more friction than a short one, though a contrary opinion seems to be prevalent. ”

“ When the bearing has been properly fitted, the crank will permit moving with one hand. If the crank shaft cannot be turned with one hand, the contact between the bearing surface is evidently too close, and the cap requires ohming up, one or two brass lines usually being sufficient. In case the crank shaft moves too easily with one hand, the shims should be removed and the steel surface of the cap filed off, permitting it to set closer. ”

“ An American inventor, Ramsey by name, is working on a motor which is said to possess great possibilities in this line. Its distinctive features include a connecting rod much shorter than usual, and a crank shaft located the length of the crank from the central axis of the cylinder. This has the effect of increasing the piston stroke, and also of increasing the proportion of the crank circle during which effective pressure is applied to the crank. ”

“ On the crank axle is a nut working on a thread at the axle centre and bearing against the end of the short sliding sleeve which constitutes the acting cone. A set screw in this central nut is loosened by inserting a wire or a nail through a hole in the bracket; the nut is held fast by putting this wire or nail into a slot therein; then a slight turn of the crank forward or back tightens or loosens the bearings at both ends simultaneously by causing the nut, thus held from turning, to move the axle to right or left instead ”

“ Those who imagine that there is a loss of power caused by the crank perplex themselves by confounding the vertical with the circumferential velocity. If the circle of the crank be divided by any number of equidistant horizontal lines, it will be obvious that there must be the same steam consumed, and the same power expended, when the crank pin passes from the level of one line to the level of the other, in whatever part of the circle it may be, those lines being indicative of equal ascents or descents of the piston. ”

“ Counterbalanced single or double crank.
174 & 175. Two forms of crank pin eccentrics; sometimes used to drive the slide valve instead of the ordinary sheave and strap, as No. 183.
176. Crank pin set in a boss formed on the driving wheel.
177. Double rod crank.
178, 179, & 181. Hand cranks. These should always be fitted with a loose ferrule of wood for the hand if possible, as much power is lost by the slipping of the hand to change its grip as the crank revolves.
180. Solid three-throw crank shaft, turned out of a solid forging. ”

“ A crank drives a shaft with a worm thread on it. The threads of the worm engage in notches in a drum. Ropes pass from the axle on which the cogged wheel drum is carried, to drums carried on a second axle. Below are parts of the machine showing its structure and also the method of fixing the rope ends. After Vidius. Power, one turn of axle only moves the cogged wheel one notch—great power therefore varying with length of crank. Power still further increased by lower axle being smaller than drums of upper. ”

“ There are special cases in which within certain limits the proportions of journals are nearly uniform in practice; thus the length of engine crank-pin bearings rarely exceeds once and a half times the diameter, while the main shaft bearings are often similarly limited in width from the exigencies of designing the engine so that the eccentric shall come in line with the slide-valve spindle. In the case of crank-pins the pin cannot be held sufficiently rigidly to prevent spring or flexure ”

“ The effort on the crank-pin is consequently made more uniform, the strength of the parts may be reduced, and the friction at slides and journals is lessened. The advantage in this respect is obviously much greater when the cylinders are placed side by side, instead of tandem, and work on cranks at right angles. As a set-off to its advantage in giving a more uniform effort, the compound engine has the drawback of requiring more working parts than a simple engine with one cylinder. ”

“ The crank shaft is a steel drop-forging having arms extending from center of shaft according to number of cylinders. It is used to change the reciprocating movement of the piston into a rotary motion of the flywheel ”

“ It is well, therefore, to have a man stationed on each side of the crank, each with a sledge hammer, and to push the crank pin in with a slam, giving the man in front orders to strike it as quickly as possible at a given signal; but if the pin does not move home so rapidly at each blow as to make it appear certain that it will go home, the man at the rear, who should have a ten-pound sledge, should be signalled to drive out the crank pin as quickly as he possibly can for every second is of consequence. ”

“ A better type of crank is made by using a steel rod for the shaft, a brass arm riveted on to it, and a steel pin riveted into that. In the portion of this chapter devoted to the horizontal engine will be found a more complete description of such a crank.
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The safety-valve, Fig. 5, is very important as a safeguard in working. Though they are sometimes omitted, yet safety-valves are essential for security. They allow steam to escape from the boiler when the pressure exceeds a certain amount, and thus the danger of an explosion is removed. ”

“ Wire nails are the best to use in putting the tracks together. The sprocket connection with the chain is shown in Fig. 3. This consists of the sprocket gear on the propelling shaft, and the crank. The pedals may be removed and a chisel handle, or any tool handle, substituted, so as to afford means for turning the crank by hand power. Great fun can be had with the road, and, furthermore, it can be made enumerative, as boys and girls can be given rides for a penny each. ”

“ The error in putting the crank on may occur from the key springing the crank out of true, and if the crank is shrunk on from too great an allowance for shrinkage or improper heating for the shrinkage or contraction, as it is sometimes termed. Referring to the error in keying, it is more liable to occur when the crank bore and its seat upon the shaft are made taper, than when made parallel, because it is a difficult matter to insure accuracy in the fit of the taper, and the key pressure will spring the crank over on the side at which it is the easiest fit. ”

“ Q. What relation to the main pin is the eccentric crank set to?
A. The eccentric crank always follows the main pin.
18. Q. Should the eccentric rod or eccentric crank break how is the engine put in condition to proceed?
A. The disabled side can have lap and lead travel and a port opening equal to the lead for all cut-offs. First block the bell crank by using a "U" bolt (which should be provided) in the holes placed in the gear frame for this purpose. Throwing reverse lever in mid-gear will help to get bell crank in position to block. ”