Equipment Operator, these troubles are easy to detect without too much checking and testing. The supervisor must, however, make the mechanics aware that there probably was, in addition, an actual or contributing cause to the power failure. The supervisor must train the mechanics to look for this cause while making repairs. Unless eliminated, this may be the cause of major trouble later on.

Too often, troubles concerned with power loss occur within the engine and are not easily found. It is these hard-to-find troubles, with little or no visual indication, that keep the CMs busy. An operator may notice a decided power loss in the equipment and, because there is excessive smoke coming from the exhaust, report the trouble as improper carburetion, or, in the case of a diesel engine, as injector trouble.

An inexperienced mechanic may notice an increased engine temperature in addition to the exhaust smoke and diagnose the loss of power as improper valve action or as trouble in the cooling system. The diagnoses are comparatively simple through visual indications. But, as a CM1, you know that there are many causes of power loss that have little or no visual indications. Examples are incorrect ignition timing, faulty coil or condenser, defective mechanical or vacuum spark advance, worn distributor cam, or slipping clutch. Any of them can cause a power loss. After a deficiency has been located in an engine, it is usually easy to make the necessary corrections to eliminate the conditions causing the deficiency. Careful analysis and straight thinking, however, are often needed to find the cause of engine deficiencies. If a supervisor has a thorough knowledge of the basic engineering and operating principles of an engine, his or her job of training the mechanics will be easier and more interesting. In diagnosing engine deficiencies, the supervisor must never jump to conclusions and make a decision on the nature of repairs to be made before being sure that what will be done will eliminate the trouble. The mechanics must be able to interpret the engine instrument indications as well as use the proper testing devices. Furthermore, they must be able to road test the equipment to determine whether repairs have been made satisfactorily and whether a part or several parts should be adjusted or replaced. Besides, the mechanic must know when and how to make emergency adjustments for every unit on the engine.

It may seem that some of the qualifications required of a good mechanic point to the know-how of an automotive engineer. However, no one person can know all about engines and also be an expert in repairing all kinds of powered equipment used by the SEABEEs. For instance, if the checks or instrument tests indicate some internal trouble in a magneto, carburetor, or fuel injection unit, the repairs should be made by mechanics who have experience or have been specially trained to use the equipment to do the particular job at hand. It is the supervisor who will be expected to have the answers to all the questions asked by less experienced me- chanics.

The three basic factors that affect an internal combustion engine's power are as follows: COMPRESSION, IGNITION, and CARBURE- TION. In the diesel engine, fuel is injected into each cylinder, and ignition depends on the heat of compression; in the gasoline engine, ignition and carburetion are independent. In both engines, of course, proper action and timing of all three factors are necessary for the engine to produce its rated power.

It is obvious then that an engine runs and develops rated power only if all of its parts function or operate as they should. If any of these parts wear or break, requiring replacement or adjustment, the performance charts and engine specifications are "tools" that will help the mechanic to bring those parts back to their original relationship to each other.

There are more factors NOT directly associated with engine working parts that must be considered in correcting engine power losses.

OPERATING CONDITIONS can affect en- gine power. For example, the usable horsepower of an engine is reduced by the number of accessories it must operate. If the engine is required to provide power for lifting operations at the same time it is delivering power to wheels or tracks, the engine may be overloaded and may not be able to develop its rated rpm; con- sequently, the rated horsepower would NOT be reached.

The effect of ALTITUDE on engine power must also be considered. As a rule, 2 1/2 percent of the output of an engine is lost for every 1,000-foot increase in elevation above sea level. Overheated air entering the cylinders has the same effect on engine power as an increase in altitude. In computing horsepower output, engineers will deduct as much as 1 percent for each 10°F rise in the intake air temperature above a "normal" temperature of 70°F.