Fig. 2332.
Yet another simple form of solid-end connecting rod is shown in [Fig. 2330], there being two brasses with a key on one side and a set-screw on the other. In this case, as soon as either brass is moved by the key it can fit the rod at the top and at the bottom only; hence there is but little to hold the brasses sideways in the rod, and furthermore the brasses are damaged from the key and the set-screw acting directly upon them, as will be explained with reference to strap-ended rods. In [Fig. 2333] is shown a very substantial form of solid-ended rod, a sectional view being shown in [Fig. 2331]. The bottom or back brass a has a flange, as shown in [Figs. 2331] and [2332] at a, which secures it to the rod end at the back. The top or key brass b has the keyway partly sunk in it, and the key binds against one side as well as on the bottom of the keyway, and this draws that brass close down to the face of the rod, as shown in [Fig. 2331].
In this as in all other connecting rods in which one edge of the key beds against the back of the brass, the taper for the key should be cut in the rod so that the edge which meets the brass will stand square across the opening for the brass; in this way the back of the brass will also stand square across, which is easier to mark off and cut, plane, and fit. If the taper for the key is cut on the brass, marking the latter and fitting it become more difficult, as it must be put in and out of its place to fit and bed the taper for the key edge, whereas, in the other case, it can be squared with a square while planing and fitting. As the bore of connecting-rod brasses wears, and the lost motion incident thereto is taken up (by driving in the key) the location of the brasses in the rod end is altered, making the rod longer or shorter according to the location of the key. But when this wear has been sufficient to let the key pass through the rod, slips of iron termed liners are inserted between the backs or bedding faces of the brasses and the end of the rod or crown of the strap, as the case may be. In putting in these liners the location of the brasses in the rod end may be adjusted so as to bring the brass back to its original position and restore the rod to its proper length, and in doing so the back brass, as distinguished from the key brass, is the one to be lined first.
Fig. 2333.
Fig. 2334.
In the rod ends shown in [Figs. 2333] and [2334] the joint faces (that is the faces where the brasses meet) must be filed away to take up the wear, hence the rods get shorter. In [Fig. 2333] the liner may be placed behind either brass, a or b, or behind both, the thickness of that behind a adjusting the length of the rod (which is always measured from centre to centre of the respective brass bores), while the thickness of that placed behind b would simply act to prevent the key from passing so far through the keyway. To prevent as far as possible the wear from altering the length of the rod, the key at one end of the rod is placed outside the crank pin or at the outer end of the rod, as in [Fig. 2333], while at the other end it is placed between the brasses and the stem of the rod, as in [Fig. 2334]. In this latter case the thickness of liner placed behind the key brass b (as the brass against which the key bears, or the brass next to the key, is always termed) would adjust the length of the rod, while the thickness of liner placed behind the back brass (as the other brass is termed) would be the one to adjust the distance the key would pass through the keyway.