Centering the Shaft.—It is necessary to check the crankshaft bearings to insure that the shaft will be square with the cylinder center lines. Two metal or wood strips, Fig. 25, should be fas tened to the ends of the engine frame, as in Fig. 26, with a piano wire stretched between. The disks should be moved until the horizontal wire just touches the three cylinder plumb lines; the wire should be leveled at the same time with the spirit level. The bearings, which haVe been placed in their housings, should be calipered to see if the line is central with each bearing. If a bearing is out, then it must be shifted until it registers central. With the wedge-type bearing this alteration can be secured by proper movement of the wedges. If the bearings are of the non adjustable shell type, it becomes necessary to scrape the high bearing and shim up the low ones.
Before the shaft is lowered on to the bottom bearing shells, small lead wires, about M2 inch in diameter, should be placed along the bottom of each bearing. When the shaft is placed in position, these wires flatten out. By raising the shaft, these wires can be removed and their thickness measured by a mi crometer. If the lead is of the same thickness throughout its length, the shaft evidently bears evenly in a longitudinal direc tion. If any unevenness is present, the shell must be scraped to a fit. To check the area of the shell which is supporting the shaft, the shaft can be coated with Prussian blue and rotated.
Upon lifting the shaft the bearing will show which points are high or low. Scraping the babbitt will bring the surface to a perfect contact.
Many erectors have the habit of using a chain sling on the shaft. This is absolutely out of place with a Diesel engine.
Sacking wrapped about the shaft and the use of rope slings will eliminate all danger of scoring the shaft. It requires only a small dent or cut on the journal to ruin a bearing. In han
dling the shaft it is advisable to suspend it by slings from each end; if possible, the slings should be tied on the shaft at other than journal points. If no traveling crane is at hand, two wooden forms, such as indicated in Fig. 24, can be constructed.
In checking up the alignment of an engine shaft already in stalled, an approximate solution is by placing one of the cranks in a horizontal position, which can be done by using a spirit level: placing the level across the two webs will prove if the shaft is out of line. This should be rechecked by reversing the level. This, of course, is only possible where the crank throws are milled on all sides.
With an engine employing an outboard bearing the alignment of the extension shaft merely necessitates the continuation of the shaft center line. In erection the main point that demands the exercise of extreme care is the bolting of the extension shaft to the main shaft, or to the flywheel, as the design may be. The flange bolts should be drawn up uniformly, a part turn of each nut in succession. Some erectors are in the habit of bolting the two parts together with the outer end unsupported by the outboard bearing. They then turn the engine over and adjust the outer bearing against the shaft end. The danger here lies in the lia bility of the unsupported shaft weight throwing it out of level. Many hot outer bearings can be attributed to this carelessness.
Plant Building.—The design of plant building is largely deter mined by instrumentalities beyond the sphere of the engineer's influence, though the layout of the machinery is essentially a matter where the operator should be considered. Figure 27 is a section through a plant containing two 500 h.p. units. The figure shows the method of piling the foundation.