_ In compensating for the wear at the big end, the wedge is taken up. Since the entire pressure acts on the wedge, the bolts must be kept snug; also there must be no binding of the bolt if fracture at the thread is to be avoided.
McEwen Diesel Connecting-rod.—This rod, Fig. 45, has both ends of the marine type. The adjustment follows standard practice. On the big end the bolts are provided with set-screws to prevent turning. These set-screws must be tightened after each adjustment. It should be understood that the taking up of the wear by removal of shims shortens the connecting-rod. This affects the compression pressure by increasing the clearance between the piston and cylinder head. A record should be kept showing the distance between the piston head and cylinder flange when the piston is at top dead-center. After taking up the wear in the pin bearings, the engine should be put on top dead-center and the clearance measured again. The increase is noted, and separators of the same thickness as the clearance increase are inserted between the rod and the big-end box. The big-end bolts are then retightened. This applies to all engines using a marine big end.
The McIntosh & Seymour Co. employs a rod of similar design.
National Transit Diesel Connecting-rod.—The National Transit Pump and Machinery Co. has adopted the form of rod appearing in Fig. 46. The big end is of the standard marine type while the piston-pin end is solid and fitted with bronze bearing shells. The wear on these shells is compensated by the adjusting screw in the rod end.
In correcting this pin wear, the rod is removed from the piston as is also the piston pin. The pin is then replaced in the bear ing and the required amount of shims inserted between the two halves, whereupon the adjusting screw is tightened. The pin is then driven out of the rod, and the piston, pin and rod are reassembled. If the pin is too tight in the brass, after being tried out by swinging the rod, the process must be repeated. Some engineers neglect the matter of the shims, but it is not advisable.
With this particular rod, since the big end does not admit of the' use of separators to bring the rod length back to normal, this correction must be made by the insertion of strips or shims between the piston-pin lower bearing shell and the rod.
Busch-Sulzer Bros. Diesel Connecting-rod.—The rod design of this engine has the big end of the marine type, separate from the rod itself. The piston-pin end is solid, having phosphor bronze bearing shells and an adjusting screw, as outlined in Fig. 47.
The method of taking up the piston-pin bearing is the same as with the National Transit engine. Since the big end is separate,
the rod length is corrected by the insertion of separators between the rod and the big end. The crank pin is lubricated by a drilled passage in the shaft, as indicated in Fig. 186. The rod is drilled its entire length and the piston pin receives its lubrication through this passage. The passage in the rod registers with the oil line in the crankshaft once per revolution, thus obtaining the proper amount of lubricant.
De La Vergne Diesel Connecting-rod.—On the P.D. Diesel engine manufactured by the De La Vergne Machine Co. the rod follows the lines of Fig. 48. This is quite like the two rods last mentioned. The unique feature is the drilled passage in the center of the rod for the purpose of oiling the piston pin. The oil is picked up from the big-end bearing, and the ports here must be kept open. It is possible for a hot big-end bearing to close the ports with flowing babbitt. This, of course, results in a ruined piston-pin bearing.
New London Ship and Engine Co. Nelseco Vertical Marine Diesel employs a connecting-rod with a marine big end and a solid piston-pin end. The latter end has a bronze bushing but is provided with no means of adjustment. If the bushing wears, it must be replaced with a new one; in an emergency the bushing can be reduced at the split and a thin shim-interposed between the bushing and the walls of the rod end. This rod can be seen in Fig. 103.
matter what the design may be, the operator some day is confronted with the problem of a big end that insists on running hot. The first move is to determine whether the lubrication has been faulty. In the majority of cases this proves the origin of the trouble. Generally the oil pipe or passage has become clogged with dirt or a bit of waste. The remedy is obvious. There is, for some unknown reason, a tend ency for the big-end bearing to wear more rapidly at one end than at the other; or, at times, both ends wear while the center remains in its original condition. This " belling " of the bearing permits the pin pressure to be distributed over a rather small area of the brass. This produces a local heating that forces the babbitt to drag, filling the oil passages and grooves. An ad ditional result of this unequal bearing wear is the scoring of the cylinder on one side. When this bearing wear has occurred, it is imperative that the babbitt be rebored to the pin diameter and the oil grooves cut. Even if the wear seems excessive, it is, as a rule, possible to avoid rebabbitting. Part of the shims between the bearing halves can be removed, and the halves clamped together and rebored to size.