The Navy uses so many models of diesel engines that it is not possible to describe in any detail all the overhaul procedures used by the Navy. Detailed repair procedures are listed in the manufacturers technical manuals and in your PMS. Always consult the manuals and the maintenance requirement cards (MRCs) before starting any type of repair work. Pay particular attention to installation tolerances, wear limits, adjustments, and safety procedures. Also be sure to follow the general rules, listed below, which apply to all engines.

1. Observe the highest degree of cleanliness in handling engine parts. Engines have been com-pletely wrecked by the presence of abrasives and various objects which have been carelessly left in the engines after overhaul. Make sure that any engine assembled for post-repair running is scrupulously free of foreign matter prior to run-ning.

Too much emphasis cannot be given to the necessity for maintaining engines clean both in-ternally and externally. Since dirt entering the engine during overhaul causes increased wear and poor operation, it is essential that all repair work be done under clean conditions. When overhaul or repair of precision parts and surfaces is re-quired, the parts and the surface should be thoroughly cleaned and wrapped in a clean cloth or suitable paper. The parts should then be stored in a dry place until reinstalled. During installa-tion, parts should be wiped with a cloth free of lint and coated, where applicable, with clean lubricating oil. When removing or installing parts such as pistons, connecting rods, camshafts, and cylinder liners, make sure that these parts are not nicked or distorted. Take precautions to keep dirt and other foreign material in the surrounding atmosphere from entering the engine while it is being overhauled. As an example, during shipyard overhaul periods the engine should be protected when sandblasting is occurring in areas adjacent to the ship.

2. Before starting repair work, make sure that all required tools and spare parts are available. Plan ahead for repair periods so everything needed is available to ensure successful and ex-peditious completion of the work.

WARNING

Never attempt to jack the engine over by hand without first disabling the starter circuit.

3. Disable the starter circuit and tagout the starter before you start working, particularly when the jacking gear is to be engaged.

4. Keep detailed records of repairs, including measurements of worn parts (with hours in use), and the new parts installed. Later, an analysis of these records will indicate the number of hours of operation that may be expected from the various parts and will facilitate prediction as to when they should be renewed before a failure occurs. Measurement of new parts are needed to determine whether or not they come within the tolerances listed in the manufacturers instruction books or the wear limit charts. In addition, before installation, all replacement parts should be com-pared with removed parts to ensure that they are suitable.

5. Do not test an overhauled diesel engine at 125% of full load or any other overload before the engine is returned to service. It has been reported that some overhauled diesel engines used for driving generators are being tested at 125% of full load before being returned to serv-ice. The original purpose for this test was to demonstrate a 25% overload capability for a 2-hour period to absorb occasional electrical peak loads. The nameplate rating of many of the older generator sets indicates a 25% temporary overload capacity. (More recent generator sets have a single rating with no stated overload requirement.) The earlier practice was a reasonable approach since the engine was frequently capable of substanti-ally greater power than could be absorbed by the generator and the 125% test was not likely to be detrimental to the engine. Now that these engines have aged, the margin of excess power available is less and the overload test is neither required nor desirable.

Another important point to remember is that if you cannot overhaul an engine due to lack of space, manpower, or expertise, you may request outside help by using an OPNAV Form 4790.2K.

This form, when used as a work request, will be sent to a Ship Intermediate Maintenance Activ-ity (SIMA). The SIMA will then accept or reject the work request. If the work request is accepted, the SIMA will order all repair parts, overhaul the engine, and perform an operational test in accord-ance with manufacturers technical manuals and NAVSHIPS Technical Manual, chapter 233.

As stated earlier in this section, since maintenance cards, manufacturers maintenance manuals, and various other instructions discuss repair procedures in detail, this chapter will be limited to general information on some of the troubles encountered during overhaul, the causes of such troubles, and the methods of repair.