Bearings, lubrication, and care of machine parts

46 CFR §61.20-23

§ 61.20-23 -23 Tailshaft clearance; bearing weardown. (a) Water lubricated bearings, other than rubber, must be rebushed as follows: (1) Where the propelling machinery is located amidship, the after stern tube bearing must be rebushed when it is worn down to 6.4 mm (0.25 in) clearance for shafts of 229 mm (9 in) or less in diameter, 7.95 mm (0.3125 in) clearance for shafts exceeding 229 mm (9 in) but not exceeding 305 mm (12 in) in diameter, and 9.53 mm (0.375 in) clearance for shafts exceeding 305 mm (12 in) in diameter. (2) Where the propelling machinery is located aft, the after stern tube bearing must be rebushed when weardown is 1.6 mm (.0625 in) less than the applicable clearance for propelling machinery located amidship. (b) Water lubricated rubber bearings must be rebushed when…

NAVEDTRA 14075 §3-3

Lubricating-oil systems The lubricating-oil system reduces friction and wear, cools the moving parts, carries away metal and combustion debris, cushions bearing shock loads, and helps seal the piston rings. In a typical wet-sump engine, a gear pump draws oil from the sump through a suction strainer and delivers it under pressure through a full-flow filter and a lube-oil cooler to the main bearings, connecting-rod bearings, camshaft, valve gear, and — through drilled passages or spray nozzles — to the underside of the piston crowns for cooling. A relief valve holds system pressure and a bypass allows oil to keep flowing if the filter or cooler becomes restricted. Large engines use a dry-sump system with a separate lube-oil tank and both pressure and scavenge pumps. Oil condition is monitor…

NAVEDTRA 14075 §4-1

Reduction gears, bearings, and shafting A propulsion engine or turbine usually turns much faster than the propeller can efficiently turn, so its output passes through reduction gears that lower the shaft speed and raise the torque to the propeller. Reduction gears use precisely cut helical (or double-helical) gear teeth that mesh smoothly and quietly and carry heavy loads; the gear teeth and the gear bearings depend on a continuous supply of clean, cool lubricating oil delivered by the gear's own lube system, and loss of that oil quickly damages the finely finished tooth surfaces and bearings. The gears are enclosed in an oil-tight casing with an oil sump, pump, cooler, and filter. Bearings support and locate the rotating shafts. Journal (sleeve) bearings carry the radial weight of a shaf…

NAVEDTRA 14075 Ch. 3 — Frictionless Bearings

Maintenance of recommended oil pressures is essential to ensure an adequate supply of oil at all bearing surfaces. Refer to the oil pressure gage as it is the best source of operational information to indicate satisfactory performance. Figure 3-23 lists the troubles that may be encountered with all types of (antifriction frictionless) bearings. Use Navy-approved, low-corrosive lubricating oils at recommended oil temperatures. Recommended temperatures have been determined by extensive tests in laboratory and in service. They are sufficiently high to assure satisfactory Since dirty bearings will have a very short service life, every possible precaution must be taken to prevent the entry of foreign matter into bearings. Dirt in a bearing which has been improperly or insufficiently cleaned may…

NAVEDTRA 14075 Ch. 3 — Gear Mechanisms

The principal type of power transmission for timing and accessory drives in most diesel engines is a system of gears similar to those shown in figure 3-24. In some of the larger engines, there may be two separate gear trains, one for driving the camshaft and the other for driving certain accessories. The type of gear employed for a particular drive depends upon the function it is to perform. Most gear trains use single helical spur gears, while governor drives are usually of the bevel type; reverse and reduction gear units employ double helical gears to balance fore and aft components of tooth pressure. Small gears are usually made from a single forging, while larger ones are quite often built up in split sections. (See the crankshaft gear in figure Chapter 3—ENGINE MAINTENANCE 121.8 Figur…

NAVEDTRA 14075 Ch. 3 — Journal Bearings

Engine journal bearing failure and their causes may vary to some degree, depending upon the type of bearing. The following discussion of the causes of bearing failure applies to most bearings—main bearings as well as crank pin bearings. The most common journal bearing failures may be due to one or to a combination of the following causes: 1. Corrosion of bearing materials caused by chemical action of oxidized lubricating oils. Oxidation of oil may be minimized by changing oil at the designated intervals, and by keeping engine temperatures within recommended limits. Bearing failures due to corrosion may be identified by very small pits covering the surfaces. In most instances, corrosion occurs over small bearings areas in which high localized pressures and temperatures exist. Since the smal…