Excessive use of water injection cools the hot device, causing the same trouble just mentioned.
An incorrect governor adjustment will produce preignitions by injecting too great an amount of oil or by allowing the normal injection to commence too early in the compression stroke. This is more evident when using light fuels.
The major part of the troubles discussed are of interest only to the operator. The plant owner does not display a great amount of concern until the engine begins to lose power and the factory machinery lags in its work. To satisfactorily operate the power plant the engineer must understand those things which cause the engine to lose its power capacity. The causes can be listed briefly as loss of compression; cold hot bulb; too heavy fuel oil; water in the fuel oil; governor or pump out of adjustment; leaky injection 'nozzle; too much water injection; preignitions; leaking air compressor, whether it be crankcase or rear of cylinder compression; clogged oil line; and in a four-stroke-cycle engine leaky valves or incorrect valve timing. The engineer can easily understand the particular adjustment necessary in each event. The items that cause the most trouble are loss of compression, water in the oil, leaky injection nozzle and defective pump valves.
Engine Pounds.—To the inexperienced engineer a pound in the engine is a source of worry and bewilderment. Most of the pounding can be attributed to four things—loose crank-pin or piston-pin brasses; worn main bearings; worn pistons; and pre ignitions.
A worn piston pin or crank pin gives out a dull pound as the piston starts back on the compression stroke, although fre quently it shows up as the piston passes the rear dead-center. This sound is different from a preignition and is seldom found on a new engine. The proper remedy is the adjusting of the partic ular brass that is worn. "Jumping" the piston and connecting rod will reveal which bearing is at fault.
The wear in the main bearings will sometimes cause a pound as the piston passes dead-center. The shaft always "jumps," and the engineer can readily detect the bearing that is worn.
If the piston is badly worn, it will-emit a slapping sound that is quite different from the bearing pounds. As discussed in the
chapter on pistons, a new piston, or in all events replacement of the worn rings, is the remedy for this slapping.
The sound of preignitions in the cylinder can hardly be mis taken for anything else. It is usually sharp and clearly defined. Any of a variety of misadjustments will cause preignitions, as already discussed.
The elimination of any of the troubles enumerated, which might be present, along with liberal lubrication of all the engine parts, will result in a smooth-running machine.
Stopping the Engine the engine is a single-cylinder unit, the stroke of the fuel pump should be gradually reduced by means of the handle. If the pump is stopped immediately without this preliminary restraint, the engine will pound badly. If the unit be a multi-cylinder engine, the fuel to all but the starting cylinder should be cut off and the starting engine used to gradually bring the engine to a state of rest.
When the engine has almost come to a standstill, the lubricat ing oil pump should be given several strokes by hand in order to supply a liberal amount of oil to all the parts. The fuel line to the pump should be drained, and the engine indkator or test cock opened. If the engine is to be idle for more than a day or two,. the oil from the crankcase and main-bearing cellars should be drawn off. The crankcase cover should be opened to allow the engine to cool unless the unit be in a dusty location. The cooling water should be allowed to circulate for at least thirty minutes after the engine is stopped. If there is any danger of frost, the cylinder jacket and water line should be drained.
The operator should carefully examine all the engine bearings, paying particular attention to the crank-pin brasses. Using a small pinch bar, this brass should be tested for clearance as well as side play. If the brass seems unusually warm, it should be disassembled and the oil grooves cleaned out. Any rough spots in the babbitt should be scraped smooth. If the crank case is enclosed, it should be drained and the slimy deposit at the bottom mopped out with a handful of waste.