Fig. 2338.
Fig. 2339.
Fig. 2340.
It will be noticed in [Fig. 2331] that the brass b does not fill the space in the rod. This is because that brass has to pass in over crank-pin collar and push up into the journal after it is in the rod. To make this space as small as possible, and to enable giving the crank pin as large a collar as possible, the key brass is sometimes beveled off, as shown in [Fig. 2336] at a b. Another form of this rod end is shown in [Fig. 2336], in which there are two keys to the brasses, the object being to adjust the keys to maintain the rod of its proper length. In order to facilitate making this adjustment, there should always be upon the face of the rod end centrepunch marks, as shown in [Fig. 2338] at f and g, or else two deep marks, as shown at c d in [Fig. 2337]. Then, in lining up the brasses to set the key back, the rod may be restored to its original length by putting behind the back brass a piece of metal of such thickness as will bring the centre of the bore of the back brass b even with the centrepunch or other marks. This being the case, it does not matter about the exact thickness of the piece of metal put behind the other brass, since a variation in that will only act to let the key come more or less through the rod end without affecting the length of the rod. In [Fig. 2337] is shown a form of rod end sometimes used. The end being open, the brasses pass through it. In this case the whole strain of the pull of the rod falls upon the edge of the gib at top and bottom of the strap, causing the gib to wear out very fast; furthermore, the back brass condenses the metal at the back of the brass opening, acting to pene it and throw the points of the rod end open, which it always does, the jaws of the gib imbedding in the jaws of the rod. This opening of the rod jaws makes the brasses loose in their places; hence this is a weak and undesirable form of rod end, though very convenient to take on and off. In [Figs. 2338], [2339], [2340], and [2341] is shown a form of solid-ended rod of more modern construction. In this case a wedge a is used instead of a key, being adjusted by screws passing through the rod at the top and bottom, it being obvious that the set-screws may have check-nuts added. b is the back brass, and c the key brass. In this case the flange of the brass goes next to the crank pin, and a plate d is provided to serve as a flange on the front face of the brass. In [Fig. 2338] this plate is removed to show the wedge a; but it is shown in the plan view, [2339], and the end view, [2340], and by itself in [Fig. 2341]. A groove is cut on each side of the two brasses and the plate spans the brasses, passing up the groove being held in position by a screw at e. The opening for the brass (in the rod end) is here shown wide enough for the rod end to pass over the collar of the crank pin, but in many cases, with this as well as with other forms of solid-ended rods, the crank pin may be made plain—that is, without a flange—and have a washer secured by a screw, so that by removing the washer the rod may be put on with the brasses already in place, and made no thicker (at the joint face) than is necessary for strength. In [Fig. 2342] is shown what may be termed a clip-end connecting rod, the screw closing the rod end (to take up the wear) against the spring of the metal. It is obvious that in this case the hole may receive a brass bush split as is the rod end and secured from turning by a pin. [Fig. 2343] presents another form of solid-end rod, which admits of the use of a brass having a flange on both sides of the strap, and will take on and off by removing the cap b. If the crank-pin collar is solid, the brasses must be placed on the crank pin, and the rod, with the wedge in place, lifted or lowered to the brasses; but if the crank pin has a washer and bolt, the rod may be put together and slipped on its place.