In [Fig. 2354] is a form of rod end in which the strap ends are keyed against abutments on the rod by means of the key a. The abutments and strap ends being bevelled, keying up the strap with a closes it down upon the rod.
Fig. 2355.
In [Fig. 2355] is a form of rod end largely used upon marine engine work; a is the end of the rod, b, b the brasses, and d, d bolts passing through the brasses. Here we have no means of correcting the alteration of length due to the wear, unless a line is marked on the rod end, as at c, and the distance that line should stand from the centre of the brass bore is marked beside it, as is denoted by the figure in the cut, indicating that the line should stand 9 inches from the cuts of the brass bore.
In general practice the inside jaw faces of connecting rod straps and the faces of the rod are made parallel, which serves very well when the duty and wear is not great; but when the wear and tear is great, as in locomotive work, it is much better to make them taper; indeed, they are in any event better taper, because in that case the brasses can be made a tighter fit. The reason for making them parallel is because they can be more readily planed so than taper; but a parallel strap is more difficult to fit, and cannot be made so good a fit as a taper one, even when new, while it is very much more difficult and expensive to repair.
Fig. 2356.
When the faces of the stub end (or, more properly speaking, of the block) are parallel one to the other, and the inside faces of the strap are also parallel, the strap must be made a very easy fit to the block, in order to be an equal fit from end to end; for if the strap fits as tightly as it should to be a good job, it will, when put on the rod, spring open, fitting across a, [Fig. 2356], only; this because the strap springs open from contact at a. The fit, then, can only be such as will not have force enough to spring the strap open, and this is very small indeed even in a very strong strap. It is within the mark to state that in a strap measuring 4 inches between jaws, at a in [Fig. 2356], it can be forced by hand on the rod sufficiently tight to spring them open 1⁄16th of an inch at b, b. When the brasses are fitted into the strap a second difficulty arises, inasmuch as they must be made a very easy fit, or else they will spring the strap open so that it will neither fit at a nor at b, whereas it is desirable that the bottom brass drive home, and the top brass, or one nearest the rod, just push home by hand.