National Transit Diesel Main 28 is the three piece bearing used on the National Transit Diesel. As will be noted, the upper part of the bearing is babbitted directly on to the bearing cap. The bottom and rear quarter consists of a single babbitted shell while the front quarter is provided with a wedge. To avoid the danger of wedge-bolt breakage, the bolt-head fits into a circular opening in the wedge. The bolt can, then, accommodate itself to any displacement of the wedge. The lubri cation is effected by two chain oilers which dip into the oil cellar east in the housing.
The Snow Oil Engine Main engine employs a bearing as illustrated in Fig. 29. • The lower shell, as well as the two quarter-boxes, is equipped with a wedge. The top quarter is a separate shell and is not cast directly on to the cap, as is usual.
The engineer will find that the bottom bearing wears most at the edge adjacent to the front quarter. The front quarter also wears at this edge.
It should be a rigid rule in every plant where oil engines are installed that no adjustment of the bearings shall be made while the engine is running. The revolving shaft allows the bearings to be drawn up tighter than when idle; the careless operator will likely tighten up the wedges enough to occasion a hot bearing. The oiling of the bearing is accomplished by means of a mechanical lubricator furnishing stream lubrication.
Allis-Chalmers Diesel Main Bearing.—A bearing has been adopted by the Allis-Chalmers Co. and appears in Fig. 30. The lower shell rests on a spherical-bottomed pad with the idea of allowing the bearing to shift to conform with the posi tion of the shaft. Since the shaft has but one true position; which must be maintained if the operation be smooth, the spherical seat is not absolutely necessary. In shimming up the lower shell, the liners are properly placed between the shell and pad. The two side quarters are equipped with wedges, while the top is babbitted directly onto the cap.
The operator, especially if he has had previous experience on steam engines, should remember that the adjustment must be made almost entirely by the front wedge and not by both quarter-boxes as in steam practice. The wedge bolts are of a design that eliminates any danger of breakage. The oiling is secured by stream lubrication from a mechanical oil pump.
Main vertical engines the wedgeless bearing, built along the lines of Fig. 31, is a common practice. The bearing is provided with a ring oiling system; generally two rings are used, and the lubricating oil is carried in a cellar in the bearing housing. Much depends on the rings working freely. Ruined bearings frequently occur where the rings cease rotating, leaving the bearing without oil. With this bearing it is absolutely imperative that the oil in the cellar be maintained at a high level. To insure 'copious lubrication the distance between oil level and point of contact of ring and shaft should be as small as possible. It is self-evident that the greater this distance is made the smaller will be the amount of oil which will reach the shaft since there is a longer time interval to allow the oil to flow back down the ring. The same reasoning applies to the grade of oil used. If it is fairly free-flowing, the shaft will receive a meager supply. The same type of bearing is adaptable to the use of a chain instead of a ring for oiling purpose. The chain should always be of brass in order to eliminate any grooving of the shaft. It is to be remembered that this brass chain will wear and break. If the bearings are not inspected occasionally, a broken chain may cause the babbitt to be ruined. It is an easy matter, when the engine is stopped, to pull a loop of the chain up through the bearing cap and run the entire length through one's fingers. Any links that are worn thin are easily detected, and, if many links are in a bad condition, the entire chain should be renewed. The advantage of the chain oiler lies in the greater amount of oil the links will carry to the shaft over that supplied by a ring oiler.
Busch-Sulzer Diesel Main Bearing.—The same general type of bearing, Fig. 32, with a pressure oilinglsystem is found on the Busch-Sulzer Engine. With this design the top and bottom shells are identical and in emergencies, when the lower shell wears, the bearing may be reversed, using the top for the bottom. There is no wear on the top shell, and a worn bearing can be used here for a time. This practice should not be main tained continually since a loose fit at the top shell may cause the shaft to whip and lift upward.