LOCOMOTIVE ENGINE. 
437 
semicircular flanches on the outside to hold them steady; and are fitted on to the crank 
pin, which is cylindrical, and five inches’ diameter, as shewn by the dotted lines in fig. 
20, and rounded out to a shoulder on each side. The brasses are held by the strap E, 
which is fixed on to the end of the connecting rod by the key E and gib G ; the key 
terminates at the bottom in a screw passing through the prolonged end, H, of the 
gib, and held by nuts. These nuts are screwed up against the end of the gib, when 
the key is driven into its place; and effectually prevent its jolting loose; the hole for 
the screw being made oblong, to allow for the side motion of the key. The holes 
in the strap E, for the key, are made rather longer outwards than the key, and the 
key-way in the connecting rod is as much longer at the inner end; causing the key 
to bear only against the connecting rod, and the gib against the strap: the strap is 
thus drawn farther on the connecting rod by driving the key, and the brasses are 
brought nearer together, and tightened up on the crank pin as they are worn by 
friction. This end of the connecting rod is shortened as much as the brasses wear ? 
as the outer brass is drawn inwards by the key; but the other end of the con 
necting rod is lengthened by the wear of the brasses, because the outer brass is 
fixed, and the inner one is pressed against it by the key. The total length of the 
connecting rod is thus kept always nearly the same, as the wear of one set of 
brasses compensates for that of the other. If this were not the case, the piston 
would be brought nearer to one end of the cylinder than the other by the wear of the 
brasses, and would require more clearance, to prevent it striking the cylinder cover. 
Cranked Axle.—The axle C' of the large wheels D', (Plate XC. and XCI.,) is 
called the cranked axle, from its having two cranks in it, to which the connecting 
rods from the two pistons are attached. It is drawn to a scale of an inch to a foot, 
or one third larger than the engravings in figs. 22 and 23, and it is shewn in the 
same position as in the Plates. It is made all in one piece and of the best wrought 
iron, termed back-barrow, or scrap-iron, and is 6-J feet long, and 5 inches in diameter. 
The axle is cylindrical at the centre part, ¿4, (fig. 22,) and is increased to five and a 
quarter inches at C C, where the cranks are formed. The two cranks, JR and L, for 
the right and left hand cylinders, are exactly at right angles to each other, as shewn 
in fig. 23, which is a section through the axle at E; the sides of the cranks D D are 
four inches thick. The crank pins JB JB are five inches diameter and three inches 
long, the same dimensions as the brasses in the ends of the connecting rods, which 
are fixed upon them ; and the length of the cranks from the centre of the axle 
to the centre of the crank pin is nine inches, which is exactly half of the stroke 
of the piston. Upon the parts F E, which are seven and a half inches long, the wheels 
are firmly fixed, so as to prevent their turning or shaking upon the axle; and 
outside the wheels, at G G, the axle is reduced to three inches and an eighth diameter