Chapter 9 Engine Troubleshooting and Overhaul

CHAPTER 3 ENGINE TROUBLESHOOTING AND OVERHAUL The engine of any piece of equipment is taken for granted as long as it runs smoothly and efficiently. But all engines lose power sooner or later from normal wear. When this happens, the mechanic must be able to determine the cause and know what is needed to correct the trouble. Generally speaking, it is not the supervisor’s job to perform engine repairs, but it is the supervisor’s job to see that these repairs are performed correctly and to assist and instruct those doing the work. Since the SEABEEs use many models of internal combustion engines, it is impossible to specify the detailed overhaul procedures for all the engines. However, here are several basic principles that apply to all engine overhauls. 1. Consult the detailed repair procedures given in the manufacturers’ instruction and maintenance manuals. Study the appropriate manuals and pamphlets before attempting any repair work. Pay particular attention to tolerances, limits, and adjustments. 2. Observe the highest degree of cleanliness in handling engine parts during overhaul. 3. Before starting repair work, be sure all required tools and replacements for known defective parts are available. 4. Keep detailed records of repairs, such as the measurements of parts, hours of use, and new parts installed. An analysis of these records will indicate the hours of operation that may be expected from the various engine parts and help in determining when a part should be renewed to avoid a failure. Since maintenance cards, manufacturers’ technical manuals, and various instructions contain repair procedures in detail, this chapter will be limited to general information on some of the troubles encountered during overhaul, their causes, and methods of repair. HORSEPOWER AND HORSEPOWER RATINGS Horsepower is a unit for measuring work per unit of time. One horsepower is equivalent to 33,000 foot-pounds of work per minute. Horsepower is determined by either measuring mechanically or computing mathematically. Maintenance manuals should be consulted for engine performance data and specifications. These manuals will also have additional horsepower designations and the many different horsepower ratings used by manufacturers in describing the equipment. The method used in measuring power and the purpose for which it is intended account for the variety of horsepower and horsepower ratings. INDICATED HORSEPOWER INDICATED HORSEPOWER is the theo- retical power that an engine would deliver if all frictional losses were eliminated. It is used mainly by experimental engineers in designing new and more efficient engines. Indicated horsepower may be computed from the following formula: Where P = L = A = N = K = 33,000 = Mean effective pressure in pounds per square inch (This is the average pressure on the piston during the power stroke minus the average pressure during the other three strokes.) Length of stroke in feet Area of piston head in square inches Working strokes per minute Number of cylinders in the engine The equivalent in foot-pounds of one horsepower per minute 3-1