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12A2. Engine stationary and moving parts. a. Cylinder block. The cylinder block is the main structural part of the engine. It is composed of forgings and steel plates welded together, combining strength with light weight.

The upper and lower decks of the cylinder block are bored to receive the cylinder liners. The space between the decks is the scavenging air chamber. The bore in the lower deck is constructed with a groove which serves as a cooling water inlet for the liner. The cylinder liners are located in the cylinder block by means of dowel pins in the upper deck.

The camshaft bearing lower support is an integral part of the cylinder block located at the extreme top of the block. The bearing cape and bearing supports are match-marked and must be kept together.

The forged transverse members in the bottom of the cylinder block form the main crankshaft upper bearing seats. Again the bearing caps and bearing supports are match-marked and must be kept together.

Fifteen removable handhole covers permit

The main bearings are lubricated from the lubricating oil manifold located in the crankcase.

b. Crankshaft. The crankshaft is a heat-treated steel forging finished all over, having eight connecting rod throws or crankpins 45 degrees apart. The crankshaft is held in the cylinder block by nine main bearing caps. The bearing at the drive end of the engine acts as a combination main and thrust bearing. Lubricating oil is supplied under pressure from a main manifold located in the crankcase, and is forced through tubes to the crankcase crossframes, where it flows through oil passages to the main bearings. From the main bearings the oil flows through drilled holes, in the crankshaft to the adjoining crankpin and lubricates the connecting rod bearing. The combination main and thrust bearing journal No. 9 is not connected by drilled holes to a crankpin. There is a 1/4-in. diameter radial oil hole in the surface of this journal into which a capscrew, with the head ground off enough to clear the bearing seat, may be inserted for rolling out the upper shell.

c. Elastic coupling. The power from the engine crankshaft is transmitted through spring packs from the inner spring holder of the elastic coupling, or flywheel, to the outer spring holder, and from there through the driving disk to the generator armature shaft flange. A pilot on the end of the crankshaft fits into a ball bearing in the armature shaft. The turning gear pinion engages a ring gear shrunk on the rim of the outer spring holder.

The inner cover of the elastic coupling, through which the camshaft gear train is driven, is fastened to the outer spring holder. A helical

Figure 12-5. Cutaway of frame, GM 8-268.

internal gear, cut in the inner bore of the elastic coupling cover, meshes with the crankshaft gear, forming a splined drive connection to the crankshaft gear which has a loose mounting on the crankshaft.

The bearing bore of the crankshaft gear. hub receives oil that flows from the adjacent main bearing through passages in the crankshaft. The parts of the elastic coupling are lubricated with the oil that flows from the bearing bore of the crankshaft gear hub.

d. Main bearings. Each main bearing consists of an upper and a lower double-flanged, bronze-backed, precision bearing shell. The centrifugally cast lining is a high lead bearing metal called Satco which contains a special hardener.

The lower shell is mounted in the bearing cap and the upper shell in its seat in the cylinder block crossframe. The joint faces of the upper and lower bearing shells project a very small amount above the seat and cap. That is to insure that the backs of the shells will be forced

into full contact when the cap is fully tightened. A drilled hole in the lower shell fits on a dowel pin in the cap. The dowel pin locates the lower shell in the bearing cap and prevents both the upper and lower shells from rotating.

Each bearing shell is marked on the edge of one flange. For example, 2-L-B.E. indicates that the shell so marked is for the No. 2 main bearing, the lower bearing shell, and the flange so marked must be toward the blower end of the engine. The main bearing nearest the blower end of the engine is the No. 1 main bearing. Upper and lower bearing shells are not interchangeable.

Crankshaft thrust loads are taken by the rear main bearing. The thrust bearing shells are the same as the other main bearing shells except that the bearing metal is extended to cover the flanges. Each main bearing cap is marked with its bearing number and is marked Blower End on the side that should face the blower end of the engine.

Lubricating oil enters the oil groove in the upper shell through a hole in the top and then

e. Pistons. The pistons are made of an alloy cast iron. The bored holes in the piston pin hubs are fitted with bronze bushings. The outer ends of the bore for the full-floating alloy steel piston pin are sealed with cast iron caps.

A cooling-oil chamber is formed by an integral baffle, and the piston crown lubricating oil under pressure flows from the top of the connecting rod, through a sealing member, into the cooling chamber. The oil seal is a spring-loaded shoe which rides on the cylindrical top of the connecting rod. The heated oil overflows through two drain passages.

Each piston is fitted with six cast iron rings, four compression rings above the piston pin and two oil control rings below. These rings are of the conventional one-piece, cut-joint type.

f. Connecting rods. The connecting rod is an alloy steel forging. The connecting rod bearing in the lower end of the connecting rod consists

The lower shell is mounted in the bearing cap and the upper shell in its seat in the connecting rod. The joint faces of the upper and lower bearing shells project a very small amount above the seat and cap. This is to insure that the backs of the shells will be forced into full contact when the cap is fully tightened. A drilled hole in the lower shell fits on a dowel pin in the cap. The dowel pin locates the lower shell in the bearing cap and prevents both the upper and lower shells from rotating.

The piston pin is of the full floating type. The piston pin bronze bushing is a shrink fit in

g. Cylinder liner. The cylinder liner is a cylindrical alloy iron casting with cored annular spaces between the inner and outer surfaces between the inner and outer surfaces through which cooling water is circulated. The liner is accurately bored to a smooth finish.

The cylinder liner is held in the engine block by the lower deckplate and a recess in the upper deckplate. The cylinder head forces the liner against the cylinder block. The lower deckplate has a groove that serves as the water inlet into the passages in the cylinder liner. It is made watertight by two synthetic rubber ring gaskets, called seal rings. The cooling water flows up through the cylinder liner and into the cylinder head through ferrules made watertight by synthetic rubber gaskets. The air intake ports, through which scavenging air from the blower enters to supply the cylinder with fresh clean air, are located around the circumference of the liner. When the piston reaches the bottom of its stroke, these ports are completely open and the air space above the piston is charged with fresh air.

The joint between the cylinder liner and the cylinder head is made gastight by an inner bronze gasket while an outer copper gasket which has notches in it serves to seat the head squarely against the cylinder liner. The drain plug in the lower part of the jacket of the cylinder liner should be removed for draining water when freezing temperatures are expected and an anti-freeze solution is not in use.

h. Cylinder heads. The engine cylinders are fitted with individual cylinder heads which are made of alloy cast iron. Studs in the cylinder block hold each head against the cylinder liner flange. The joint between the head and the liner is made gastight with an inner bronze and an outer copper gasket. The outer gasket serves to seat the head squarely on the liner. The shallow milled grooves show leakage of exhaust gas or water.

The head is also fastened to the vertical wall of the cam pocket with tap-bolts. The joint is made oiltight with a synthetic rubber gasket.

Cooling water flows from the cylinder liner into the head and then flows into the water jacket of the exhaust manifold.

Each cylinder head is fitted with four exhaust valves, the unit injector, rocker lever assemblies, air starter distributor valve, an over speed injector lock, the air starter check valve, and the cylinder test and safety valves.

i. Rocker lever assembly. Each cylinder head is equipped with three rocker levers, two of which operate the two pairs of exhaust valves, and the third operates the injector. The rocker levers are made of alloy steel forgings. Bushings are pressed into the lever hubs and are reamed for a bearing fit on the rocker lever shaft.

The three rocker levers rock on a fixed shaft which is clamped in a bearing support. They are fitted with cam rollers, which operate in contact with the exhaust and injector cams. Each of the three cam rollers turns on a bushing and the bushing turns on a sleeve that has a loose mounting on the roller pin. Each of the exhaust valve rocker levers operates two valves

The rocker lever shaft is made of alloy steel and is ground to size. The shaft is clamped in the bearing support by two bearing caps and is held in its correct location by a dowel pin in one of the bearings. A rocker shaft thrust plate is bolted to each end of the shaft, and a plant fiber gasket is placed in the joint between the thrust plate and the rocker lever shaft. The bearing support is fastened to the cylinder head with two studs and positioned by two dowels, and is also held against the head by two of the cylinder head hold-down studs.

The rocker lever assembly is lubricated with oil received from one of the camshaft bearings. The oil flows from the top of the camshaft bearing through a tube to the plate connection that is fastened to one end of the rocker lever shaft. From this connection, the oil flows through drilled passages in the rocker lever shaft to the three bearings in the rocker lever hubs.

A drilled passage in each of the rocker lever forgings conducts the lubricating oil from a hole in the hub bushing to the camshaft end of the lever. The rocker lever motion permits oil to flow intermittently under pressure from the hole in the shaft, through one hole in the bushing and rocker lever to the cam roller. The bearing in each of the cam rollers receives oil through drilled holes in the roller pin and in the bearing bushings.

j. Camshaft drive. In 2-cycle engine operation the camshaft rotates at the same speed as the crankshaft. The camshaft drive gears are located at the power takeoff end of the engine. They transmit the rotation of the crankshaft to the camshaft. It is necessary to maintain a fixed relationship between the rotation of the crankshaft and the rotation of the camshaft so that

Steel-backed babbitt-lined bearing shells support the inner and outer hubs of the forged steel helical idler gears. The inner and outer supports are bolted and doweled together before being mounted in the camshaft drive housing. The fuel oil pump and governor are driven from a gear that meshes with the lower idler gear. A pair of bevel gears drives the vertical governor shaft which is mounted in ball bearings.

The lower idler gear also drives the quill shaft gear, which is splined for the quill shaft that drives the blower and accessory gear trains. A splined coupling, which rotates in the babbitt-lined center bearing, joins the two sections of the quill shaft.

The overspeed trip weight assembly and the camshaft gear are bolted and doweled to a hub that also serves as a bearing journal for this assembly. The hub is splined to fit on the end of the camshaft.

Lubricating oil for the camshaft drive gear train and bearings is piped from the end of the lubricating oil manifold in the cylinder block. Oil is supplied under pressure to the hollow camshaft through the camshaft gear bearing. Open jets spray oil on the gear teeth.

Complete dynamic balance of the engine is obtained by balance weights mounted in a certain relation to each other on the gears in the front and rear gear trains.

k. Accessory drive. The accessory drive, located between the end of the crankcase and the blower, consists of a train of helical gears driven from the camshaft drive gear train through the quill shaft. The gears in the accessory drive are match-marked with a definite relationship to the match-marks on the gears in the camshaft drive gear train, to maintain the

The accessory drive gear drives the upper idler gear. This upper idler gear drives the lower idler gear. A plate with a splined hub for driving the lubricating oil pump is bolted to the hub of the lower idler gear. The fresh water and sea water pump drive gears are driven from the lower idler gear. The hubs of the water pump drive gears have a spline cut in the bore for the fresh water and sea water pump shafts. The hubs which project from each side of the lower idler and water pump gears run in steel-backed babbitt-lined bearings mounted in the inner and outer bearing supports. These bearing supports are bolted together and the assembly is fastened in place on the inside of the accessory drive housing.

Lubricating oil is piped to the accessory drive from the main lubricating oil manifold in the cylinder block. Oil lines and connecting pass ages in the bearing supports supply oil to the bearings in the drive.

The accessory drive cover should be removed periodically and the gear train inspected for excessive wear of any parts. Lubricating oil lines and passages should be checked periodically to insure that they are not broken or clogged. All nuts and capscrews should be tight.

1. Camshaft. The camshaft is of the one-piece type with integral case-hardened cams and bearings. The bearing bushings, which are

There are four cams for each cylinder. The two outer cams operate the exhaust valves, and the center cam operates the injector. The fourth cam, which is narrower than the other three, operates the air timing valve.

The camshaft drive end of the camshaft is splined for a driving connection in the hub of the camshaft gear which is driven from the crankshaft gear through a train of idler gears.

Lubricating oil under pressure is supplied to the camshaft bore through the splined drive connection. The oil is then delivered to the camshaft bearings through radial holes in the camshaft. Oil for lubricating the rocker lever mechanisms flows through tubes from the camshaft bearing caps.

m. Engine control. The governor, which is located at the generator end of the engine, controls the engine speed for any setting.

The movement of the governor power mechanism is transmitted through lever and link connections to the injector control shaft in the cam pocket. Each fuel injector rack is connected to a control shaft lever through a slipjoint link. A micrometer adjusting screw on this link increases or decreases the amount of fuel injected into the combustion chamber.

A slip joint is connected to each injector rack so that in case the control rack in one injector binds, the compression of the spring in

The start and stop lever is used for manual control when starting or stopping the engine, and its movements are transmitted through a connection that provides for unrestricted governor control when the start and stop lever is latched in the RUN position. The governor connections to the injector control shaft include an extensible spring-loaded link which permits the injector control shaft to be turned manually without moving the governor power piston.

When the governor or any part of the injector control system is renewed, the governor power piston should be linked in the correct relation to the injector rack.

n. Overspeed trip. The overspeed trip mechanism stops the injection of fuel oil to the combustion chambers when the engine speed exceeds 112 percent of rated speed.

The overspeed trip weight assembly, mounted on the camshaft gear, is fitted with a spring-loaded flyweight. The spring tension is adjusted so that, at a predetermined engine overspeed, the centrifugal force moves the flyweight radially until it strikes a roller latch, releasing the spring-actuated injector lock shaft in the cam pocket at each engine cylinder. The injector lock carries a lever on the shaft that moves a pawl engaging a notch on the injector rocker lever. The injection of fuel stops when the locked rocker lever holds the injector plunger at the lower end of its pumping stroke.

The overspeed trip is manually reset with a hand lever on the shaft which projects from the camshaft drive housing.

12A3. Fuel oil system. a. Description. The fuel oil pump draws oil from the clean fuel oil tank and forces it through the fuel block and the fuel oil strainer and filter. From the filter, the oil flows to the fuel supply manifold, which is the third pipe from the top in the multiple oil pipe assembly, and then through a small jet

The surplus fuel is bypassed in the injector and flows through another filter in the injector outlet passage so that any reverse flow of fuel cannot carry dirt into the injector. The surplus fuel passes from the injector through a tube to a fuel bleed manifold, which is the bottom pipe in the multiple oil pipe assembly. The fuel from this bleed manifold flows to the metering block, through the metering valve which sets up enough resistance to maintain the required pressure in the fuel supply manifold, and then flows back to the clean fuel oil tank.

Fuel oil leakage from the injector plunger and bushing is drained through an injector body ferrule, through a cylinder head passage into a manifold connection clamped between the cylinder block and cylinder head. The injector drainage is conducted through this connection to the second manifold from the top in the multiple oil pipe assembly and then it flows through the drain to the fuel oil tank or bilge.

b. The unit injector. On this engine, the fuel pump and spray valve are combined into a single and compact unit called a unit injector, which meters the fuel and also atomizes and sprays it into the cylinder. This injector is similar to that used in the GM 16-278A and its operating principle is identical. The unit injector is held in position in a water-cooled jacket in the center of the cylinder head: At the lower end, the injector forms a gastight seal with the tapered seat in the cylinder head. All the injectors in this engine are alike and interchangeable. Fuel is supplied through jumper tubes with spherical type gasketless connections.

The pumping function of the injector is accomplished by the reciprocating motion of the constant stroke injector plunger which is actuated by the injector cam on the engine camshaft, through the injector rocker lever.

The position of the plunger, and thereby the timing, is adjusted by means of the ball stud and lock nut at the injector end of the rocker lever.

The quantity of fuel injected into each cylinder, and therefore the power developed in

c. Fuel block. The fuel block is located under the exhaust manifold at the camshaft drive end of the engine and in front of the fuel oil pump. The fuel block contains a metering valve, a priming valve, and an adjustable pressure relief valve.

d. Jet filters. The cylinder head jet filters are located on each head, just above the exhaust manifold connection. The element in each cylinder head is of the edgewise-wound metal ribbon type. This filter is correctly assembled when the helical spring and cap are placed over the long end of the filtering element to hold the element flange against the shoulder at the inner end of the filter wall.

e. Fuel pump. The fuel oil pump is located under the exhaust manifold at the camshaft drive end of the engine and is of the positive displacement, spur gear, rotor type. Fuel enters the pump through the top port in the end of the pump and is discharged from the lower port on the side of the pump. Each pump gear is keyed to its shaft by a pin.

f. Fuel oil strainer. The fuel oil strainer contains two straining units, each with an inner and outer winding. The space between the windings on the inner and outer elements is 0.001 in.

Fuel oil enters the strainer case, flows through the outer and inner windings, through the center of the elements, and out through the strainer head. Provision is made for using either one or both strainer units. When the handle on the unit is shifted to the No. 1 position, the oil is flowing through the No. 1 unit. This applies also to the No. 2 position. When the control valve is in the Both position, oil is flowing through both units. This is the position of the control valve for normal operation. The positions of the control valve and the number of the corresponding straining unit are cast into the strainer head at the control valve.

g. Fuel oil filter. The fuel oil filter is a duplex filter with provisions for using either one

or both filtering units. In normal operation both filtering units are in operation.

The arrows under the valve handles show the positions of the valve handles for using either one or both of the units. The flanges are also marked IN and OUT indicating the direction of flow of fuel oil through the filter. When the valve handles are between the two positions indicated on the valve handle base, or with the valve handles directly above the inlet and outlet flanges, fuel oil is passing through both units. If the valve handle on the IN end of the filter is in one of the positions indicated by the arrow on the casting, the valve handle on the OUT end of the filter must be in the corresponding position. The flow of fuel oil to the engine will be stopped if both valve handles are not pointing in the same direction when using only one filtering unit.

12A4. Lubricating oil system. a. Description. The lubricating oil pressure pump, mounted directly below the blower, draws hot oil from the oil pan through a strainer in the

Lubricating oil is supplied to the lubricating oil manifold in the cylinder block. From this manifold, oil is forced through tubes to the crankcase crossframes, where it flows through oil passages to lubricate the main bearings. The crankpin bearings are lubricated with oil received from an adjacent main bearing through oil passages in the crankshaft. Oil holes in the

The camshaft drive gears are lubricated with oil from the generator end of the lubricating oil supply manifold in the engine block. Oil is piped from this manifold to the camshaft drive gear bearing support and to the lubricating oil distribution block in the camshaft drive housing. Lines from the distribution block carry oil to the other gear bearings in the camshaft drive and the mating teeth of the gears in the camshaft drive. The lubricating oil from the camshaft drive housing is returned to the engine oil pan by the camshaft drive housing scavenging pump.

Oil under pressure is supplied to the camshaft bore through the splined drive connection. The oil is then delivered to the camshaft

bearing through radial holes in the camshaft. Oil for lubricating the rocker lever mechanism flows through tubes from the camshaft bearing caps. This oil also furnishes lubrication for the valve assembly. The oil then drains to the oil pan.

The blower and accessory drive gear bearings receive oil from the blower end of the lubricating oil pressure manifold in the engine block. Oil for the blower bearings and gears is received from the relief valve connection on the main lubricating oil manifold, and then is conducted through the tubes under the rotor housing to passages in the blower endplates, and returned to the oil pan.

b. Lubricating oil pump. The attached lubricating oil pump unit is mounted below the blower. The pump unit is of the positive displacement, helical gear type, and consists of a lubricating oil pressure pump, a camshaft drive housing scavenging pump, and a generator bearing scavenging pump. The lubricating oil pressure pump supplies lubricating oil to the engine. The camshaft drive housing scavenging pump

Figure 12-13. Cutaway of lubricating oil cooler GM 8-268.

draws the oil from the camshaft drive housing and returns it to the engine oil pan. The generator bearing scavenging pump draws the excess oil from the generator bearing and returns it to the engine oil pan. The pump housing is made in four separate parts: the bearing flange, the generator bearing scavenging pump housing, the camshaft drive housing scavenging pump housing, and the lubricating oil pressure pump housing. The driving gear shaft bearings are located in the pump housing. The driven gears, fitted with bronze bushings, rotate on the stationary idler gear shaft.

c. Strainers. Two types of strainers are used in this installation. The lubricating oil suction strainer is located in the pump intake line at the blower end of the engine and strains the oil entering the pump from the engine lubricating oil pan. The straining element is made of wire screen and is in the shape of a cylinder. The pump draws oil through the open end of the strainer element and sends it out through its side.

The direction in which to rotate the cleaning handle is indicated by an arrow. The pressure drop through the strainer is an indication of the condition of the straining element.

The other lever on the strainer operates the bypass valve. When the lever is in the ON position the lubricating oil is flowing through the strainer. When the lever is in the BYPASS position the oil is flowing directly through the head of the unit, and the strainer case and element can be removed and cleaned. The ON and BYPASS positions are indicated on the strainer case.

d. Lubricating oil cooler. The lubricating oil is cooled in a Harrison type cooler that is made up of a core assembly and an enclosing case. The oblong tubes enclose a series of baffles which form a winding passage for the flow of oil. The tubes are fastened to header plates at the ends. The core assembly is permanently attached to the casing.

12A5. Cooling system. a. General. The cooling system is of the closed type, employing fresh water to cool the engine, with salt water in the generator air coolers and acting as the cooling agent in the fresh water cooler.

b. Salt water system. The salt water pump draws water from the sea chest through a strainer and forces it through the engine water cooler and out through the overboard discharge. The pump also forces sea water through a branch line to the generator coolers. The valve controlling the flow of salt water through the generator coolers should be set to keep the temperature of air in the generator at the temperature specified in the manufacturer's instruction book.

c. Fresh water system. The fresh water pump forces the water into the engine water

d. Fresh water and salt water pumps. The fresh water and salt water pumps are of the, centrifugal type. Water enters the center of the impeller and is thrown outward through the impeller vanes by the rotating motion of the pump.

The pump impeller is keyed to the tapered end of the driving shaft and rotates in the pump housing on two pairs of replaceable bronze wear rings.

A packing sleeve is keyed to the shaft and butts against the impeller. A watertight seal is provided by three 1/8-in. square plastic metallic packing rings that fit in a recess of the packing sleeve. This packing is tightened by rotating the locking sleeve with a spanner wrench, thereby compressing the packing. The sleeve is locked in place with a setscrew. The packing gland must be removed and the setscrews loosened before the locking sleeve can be tightened.

A finger, locked to the shift with a setscrew, throws off any water that may work its way along the shaft toward the ball bearing. The ball bearing is pressed on the shaft and can be removed only with the bearing puller furnished for this purpose. This bearing is lubricated by splash from the accessory drive. A leather seal prevents the oil from leaking out of the bearing housing.

e. Fresh water cooler. The engine water is cooled in a Harrison type cooler consisting of a core assembly and an enclosing case. The oblong tubes are baffled to form winding passages for the flow of engine water. The tubes are fastened to header plates at the ends. The core assembly is permanently attached to the casing.

12A6. Air intake and exhaust systems. a. General. An air blower scavenges the engine

Air is drawn by the blower through an intake silencer and is discharged through a distributor manifold into the air box surrounding the cylinders. Air is admitted to each cylinder when the piston uncovers the intake ports. These ports are designed to produce a swirling flow of air upward through the cylinder toward the exhaust valves which open for the discharge of the exhaust gases. This results in complete scavenging and filling of the cylinders with clean air.

The exhaust gases from each cylinder are discharged into a water-jacketed manifold, which in turn discharges the gases into one of the main engine exhaust pipes (usually No. 3ME) and thence to the atmosphere.

The cooling water flows from each cylinder head into the water passages of the manifold.

Thermocouples for measuring the temperature of the exhaust gases from each cylinder are located in the manifold.

b. Blower. The blower consists of a pair of rotors revolving together in a closely fitted housing. Each rotor has three helical lobes which produce a continuous and uniform displacement of air. The rotors do not touch each other or the surrounding housing. Air enters the housing at one side and fills the spaces between the rotor lobes as they roll apart. The air is carried around the cylindrical sides of the housing, into the closed spaces between the lobes and the housing, and is forced under pressure to the discharge side of the housing as the lobes roll together. Then the air passes through a distributor manifold into the air box around the cylinder liners.

Each rotor is carried by a tubular serrated shaft. Endwise movement is prevented by two taper pins. No gaskets are used between the

endplates and the housing due to the importance of maintaining the correct rotor end clearance. A fine silk thread around the housing, inside the stud line, together with a very thin coat of non-hardening gasket compound, provides an airtight seal.

Large babbitted bearings in the endplates accurately locate the rotors in the two half-bores of the housing so that the clearances between the rotor tips and the housing bores can be held to a minimum. Both ends of the rotor bearings at the gear end of the blower are made with thrust surfaces that locate the rotor endwise and prevent contact between the rotors and the endplates.

The power to drive the blower is transmitted directly to the rotor gear train by a drive shaft that extends through a passage in the blower housing. Closely fitted helical rotor gears are rigidly attached to both rotor shafts to prevent the rotors from touching each other as they roll together. Each hub is pressed on the serrated rotor shaft. A

The blower rotor gears are bolted to the gear hub flanges and are located angularly by hardened dowel pins. Due to the importance of having the rotors roll together without touching, yet with the least possible clearance, it is necessary to locate the dowel pins during the assembly for a given set of gears and hubs. This is the only adjustment provided for timing the gears with respect to the rotors.

Oil passages in the endplates conduct lubricating oil under pressure to the bearings. Oil seals are provided at each bearing to prevent oil from entering the rotor housing.

c. Air maze. A breather system is used to prevent contamination of the engine room atmosphere by heated, fume-laden air that otherwise would escape from the engine crankcase. This ventilation of the crankcase also reduces the formation of sludge in the oil and prevents the accumulation of combustible gases in the crankcase and oil pan.

Atmospheric air for the breather system enters the engine through the cylinder head cover breathers. The blower draws air from the crankcase through the air maze which prevents oil mist from being drawn into the blower.

The air maze element consists of a number of fine steel and copper wire screens. Oil laden air is drawn through the air maze screens. The oil deposited on the screens, drains to the bottom of the air maze housing. This separated oil is returned to the accessory drive cover through a drain tube.

12A7. Air starting system. High-pressure air is piped to a lever-operated air starting valve. When the lever opens the valve, it allows the air to flow through the starting air manifold in the cam pocket of the crankcase to the individual air distributor valves or air timing valves in the rocker lever bearing support at each cylinder. The distributor valve is of the poppet type and is operated from the narrow earn in each group of four on the engine camshaft. Starting air from each distributor or timing valve is conducted

The engine operates on the two-cycle principle in which two strokes of each piston and one complete revolution of each crankshaft are necessary to complete the cycle. The cycle begins with the movement of the pistons from their outer dead centers. As the pistons move

Toward the end of the expansion stroke, the lower pistons uncover the exhaust ports and allow the burned gases to escape to the atmosphere through the exhaust system. Soon afterward, the upper pistons uncover the air inlet ports. At this point the pressure in the cylinder is about atmospheric. As the inlet ports are uncovered, the scavenging air under pressure in the air receiver rushes into the cylinder with a whirling motion, sweeping the cylinder clear of any remaining exhaust gas and filling it with fresh air for the next compression stroke. The whirling motion or turbulence of the air is obtained by the tangentially cast inlet ports. This turbulence persists throughout the injection period and aids in the mixing of the air and fuel.

With this arrangement of the pistons and crankshafts as described above, the lower crankshaft will lead the upper crankshaft by approximately 12 degrees. The difference in the crankshaft setting is referred to as the lower crank lead. The two pistons will be the nearest together when the upper piston is approximately 6 degrees ahead of inner dead center and the lower piston is 6 degrees past inner dead center. The point midway between the two pistons when they are in this position is called the piston dead center.

From the foregoing it can be seen that when the upper piston reaches inner dead center, the lower piston will have completed 12 degrees of the expansion or power stroke. This causes the lower piston to receive the greater part of the expansion force with the result that at full load about 70 percent of the total load is delivered by the lower crankshaft. The remaining power is delivered to the upper crankshaft where it is partially utilized in driving the scavenging blower. Any residual power is transmitted through the vertical drive gear to the lower crankshaft which is connected to the generator.

12B3. Engine main moving and stationary parts. a. Cylinder block. The cylinder block is the main structural part of the engine and is designed to give it the necessary strength and rigidity. It is constructed of hot rolled steel plates of the proper dimensions welded into a single unit, combining compactness and strength with lightness of weight.

Transverse vertical members together with horizontal decks form enclosures, housings, and fastenings for the operating parts of the engine. The four horizontal decks are bored to receive the cylinder liners along the centerline of the engine. An extension of the block is provided for attaching the scavenging air blower at the vertical drive end of the engine.

The cylinder block is separated into the following compartments:

1. The control end compartment which forms an enclosure for the timing chain, controls, overspeed and timing governors, and drives for the regulating governor and attached pumps.

2. The vertical drive compartment which houses the vertical gear drive that interconnects the upper and lower crankshafts. Used oil from the drive gears and upper crankcase compartment drains down through this compartment to the oil pan or engine sump.

3. The upper crankcase compartment which forms the bearing saddles for the upper crankshaft bearings and bearings hubs for the camshaft bearings. The saddles and bearing hubs are drilled for passage of lubricating oil to the bearings from the upper oil header. The used oil from these parts collects on the floor of this compartment and drains way from the center of the block toward each end where it passes through openings to the engine sump or oil pan.

4. The air receiver compartment which extends the full length of the block and completely surrounds the cylinder liners at the air intake ports, forming a passage for scavenging air from the blower to the inlet ports of the cylinder liners.

5. The injection nozzle compartments

6. The exhaust compartment which extends the full length of the block on each side. The exhaust decks are bolted to the block and surround the cylinder liner, forming water-cooled passages for the exhaust gases from the combustion spaces to the exhaust manifolds. The manifolds are water-cooled welded steel units, bolted to the cylinder block and exhaust decks.

7. The lower crankcase compartment which forms bearing saddles for the lower main and thrust bearings. These saddles are drilled for the passage of lubricating oil to the bearings. The used oil from the engine collects in the oil pan or engine sump.

After welding, the block is sand blasted and stress relieved to remove the internal strains at certain vital points. It is then magnafluxed to check for the presence of any construction faults. The various compartments are provided with covers. The upper crankcase compartment is closed by a top cover bolted to the block. The cover has several inspection covers along the top, one of which is an explosion cover to relieve any excess pressure built up in the upper crankcase. An explosion cover on the control end of the block above the exhaust nozzle prevents the possibility of excess pressure building up in the lower crankcase.

The main and thrust bearing saddles are machined together with the forged steel bearing caps. These are match-marked to show proper position. When a replacement cylinder block is ordered the bearing caps are always furnished in place.

b. Cylinders and cylinder liners. The cylinders are formed by cylindrical sleeves or liners located on the centerline of the engine and spaced to correspond with the crankshaft throws. The cast iron liners have specially designed air inlet and exhaust ports for the passage of scavenging air to, and of exhaust gases from the combustion space.

The liner cooling spaces are formed by

Openings for the air start check valve, cylinder relief valve, and injection nozzle are located in the liner and liner jacket at the point where the pistons arrive at inner dead center.

The channels directing the cooling water up and around the cylinder liner are cast in between the ribs on the liner. The heat of combustion that accumulates in the cylinders, as well as the heat conducted to the air start check valve, cylinder relief valve, and injection nozzle, is transferred to the cooling water which flows into these passages through regular fittings from the water jacket of the exhaust manifold. The water leaves the cylinder liner near the top of the jacket by means of an outlet pipe to the water header.

c. Crankshafts and main bearings. The crankshaft is a heat-treated, cast iron shaft with an allover finish. It is held in the cylinder block by main bearing caps. The bearing at the blower end of the upper crankshaft and at the coupling end of the lower crankshaft act as combination main and thrust bearings. The crankshaft is drilled from each main bearing journal to each connecting rod journal so that oil, furnished to the main bearing saddles from the oil headers, flows into the crank and into each connecting rod journal. The combination main and thrust bearings are not connected to any connecting rod journal; accordingly they are not drilled, but receive their oil from separate tubes direct from the oil headers.

d. Vertical drive assembly. The power developed by the upper crankshaft is transmitted to the lower crankshaft by means of a gear drive which is turned by the crankshaft gear bolted to the blower end of each crankshaft. The drive assembly consists of two tapered shafts with pinions, connected together by a flexible coupling with laminated rings between the hubs, coupling shaft, and adjusting flange. The upper and lower housings contain a large and a small set of thrust bearings.

e. Connecting rod and connecting rod bearings. The connecting rod is an alloy steel forging with a closed eye at one end and a removable

f. Piston and piston pin assembly. The upper and lower cast iron pistons are identical except for the position of the fuel opening in the cup at the top of the piston. The pistons are marked and should be installed in their proper places, so that the fuel openings line up correctly with the injection nozzle openings in the liners.

The pistons are connected to their respective crankshafts by the piston pin bracket, piston pin, needle bearings or bronze bushing, and forged steel connecting rods, and are cooled by lubricating oil as described later.

Each piston is fitted with seven cast iron rings, four of which are compression rings located above the piston pin and three of which are oil rings located below the piston pin. Of these three rings there is one oil scraper, one oil drain, and one oil cutter ring.

The condition of the lower piston and rings may be observed through the exhaust manifold and ports after the thermocouple or plain covers have been removed from the manifold.

g. Camshaft, camshaft stub shaft, and camshaft bearings. The camshaft is of the one-piece type with integral cams on a case-hardened alloy steel shaft. There is one cam on the camshaft for each cylinder. This cam actuates the injection pump plunger. There is only one camshaft on this model F-M engine. On the other side of the engine from the camshaft is a camshaft stub shaft which is used to drive various governor auxiliaries and to form a part of the timing chain system. This stub shaft is extremely short, extending for the length of one cylinder only.

The camshaft bearings are held in place in the block by special setscrews. Exceptions to this

h. Timing chain. The timing chain is the means by which the rotation of the upper crankshaft is conveyed to the camshafts, turning the camshafts at the same rate of speed as the crankshaft. Sprockets are fastened to the control end of the crankshaft, camshaft, and stub shaft. The chain is guided by special links over the crankshaft sprocket, under a timing chain sprocket, and over the camshaft sprocket. It then passes under a tightener sprocket, over the stub shaft sprocket, and under a second timing chain sprocket to the crankshaft.

The timing chain is a No. 766 Duplex 1/2 in. pitch, 2 in. wide, center guide, endless chain of 116 pitches. It is assembled to operate the links, to guide the chain on the camshaft and crankshaft sprockets, and to operate in slots in the tightener and timing sprockets.

i. Hand control lever. The engine is started and stopped by means of a hand-control lever. This lever has three positions: START, STOP, and RUN. In the STOP position, the fuel cutout cam on the control shaft moves the fuel injection pump control rod to the no fuel position. When the lever is in the START position, the control shaft mechanism moves the air control valve plunger and opens the control valve, admitting air to the engine air header and air distributor. In the RUN position, the engine is under full governor control.

j. Emergency stop and reset lever. The engine is equipped with a hand-operated emergency stop device, consisting of a push button that operates against the overspeed latch and releases the overspeed stop plunger, shutting off the delivery of fuel to the injection pumps. This emergency stop may be connected to the ship's air supply so that it can be operated from the maneuvering room by the use of a quick opening valve to stop the engine. When air pressure is admitted to the emergency stop housing, the overspeed stop latch is tripped and shuts off the

k. Overspeed governor. The overspeed governor mechanism automatically stops the engine when the main governor fails to hold the engine speed below the safe maximum of 1290 to 1370 rpm. This mechanism consists of a weight on the end of, and rotating with the camshaft. When an overspeed condition occurs, movement of the governor weights releases the spring-loaded stop device as described below.

When the predetermined safe speed of the engine is reached, the centrifugal force of the governor weight will overcome the opposing pressure of a spring and allow the governor weight to swing outward and strike the governor lever. This trips the overspeed stop latch and releases the overspeed stop plunger which moves fuel cutout lever and shaft, shutting off the supply of fuel to the injection pumps. The speed at which the governor weight will strike the governor lever can be adjusted by the addition or removal of shims. At regular intervals this governor

In order to start the engine after it has been stopped by either the overspeed governor or the emergency stop, the plunger must be returned to its spring-loaded normal position. This is accomplished by moving the reset lever which in turn moves the reset shaft and pulls the stop plunger up, thus compressing the spring to a position where the overspeed latch will be brought up back of the head on the plunger by the stop latch spring. The reset lever is then in its normal position and the engine is ready to operate.

1. Flexible drive. The flexible drive transmits power from the lower crankshaft to drive the governor, air start distributor, lubricating oil pump, and fuel oil and generator bearing drain pumps.

The pump drive hub is pressed on to the lower crankshaft, and the pump drive gear is bolted to it.

The lower torsion graph drive shaft is

The power take-off for the air start distributor and the governor is located in the pump drive housing and consists of a gear keyed to the pump drive shaft and driving a final spiral gear.

The lubricating oil pump is bolted to the pump mounting plate and is connected to the pump drive shaft by a positive drive coupling. At the end of the lubricating oil pump impeller driving shaft is a set of beveled gears that drive the fuel oil and generator bearing drain pumps. These pumps are located on each end of the fuel pump drive housing.

The fresh water and salt water pumps are driven directly from the pump drive gear.

13B4. Scavenging system and blower. a. General description. Scavenging air is supplied to the cylinders under a pressure of from 2 to 5 psi by means of a positive displacement type blower. The blower consists of a housing containing inlet and exhaust passages enclosing two three-lobe spiral impellers. Timing gears, driven by a gear drive from the upper crankshaft, interconnect the impellers.

Air is drawn from the atmosphere through the air silencer and enters the inlet passage of the blower. It is moved by the lobes along the walls of the blower housing and forced through the outlet passages. Pipes conduct the scavenging air to the air receiver compartments on each side of the cylinder block. These receivers are the full width of the cylinder block and extend to the control end compartment. They completely surround the cylinder liners at the air inlet ports. The scavenging air enters the cylinder under pressure, and sweeps the exhaust gases out through the exhaust ports, producing complete scavenging. A quantity of scavenging air is trapped in the cylinder by the pistons, thus providing fresh air for the next compression stroke.

The scavenging air is discharged from the blower with a uniform velocity due to the design of the impeller lobes. For greatest efficiency the clearances between the impellers, the impellers

b. Oil separator. The engine crankcases, vertical drive, and control end compartments are vented by means of the suction of the blower. A slight vacuum is produced by suction through an oil separator located inside the blower end cover. This should be adjusted to 2 in. maximum water vacuum by the screw on top of the oil separator in the blower end cover. Passage to the oil separator is through the hollow impeller shafts.

The separator consists of a metal box, with small holes drilled in the front piece, filled with copper gimp upon which the oil collects as the air passes through it. The accumulated oil is drained off each end of the separator, collecting in the lower compartments of the blower and draining back into the crankcase.

The separator should be removed and cleaned in kerosene at regular intervals. The excess oil should be blown from the copper gimp before placing the separator back into service. If for any reason the separator is neglected, the seepage of oil from the lower crankcase side cover or a possible smoky condition of the exhaust will indicate that it should be cleaned.

12B5. Fuel system. a. Description. The fuel oil supply system is composed of a standby and priming pump, an attached fuel oil pump, and a fuel oil strainer-filter with the necessary relief valves and piping.

The standby and priming pump is used to fill the complete fuel system prior to first starting the engine or after the engine has been over hauled. As the engine starts to turn, the attached fuel oil pump takes over the task of supplying fuel to the engine and forces the fuel past a relief bypass valve through the fuel oil strainer-filter to the engine header where each individual injection pump is supplied. The overflow from this header is directed, via a relief valve, to the clean fuel oil tank. Dirty oil from the injection nozzle compartment flows back to the leakage tank or to the bilges depending on the particular installation.

The capacity of the supply pump is such

b. Fuel pump. The attached fuel oil supply pump is a positive displacement pump. It should require no attention other than an occasional inspection. The packing gland should be tightened or repacked as found necessary. It is very important when installing pump packing that the rings be cut to the exact lengths. The joints of the packing should be alternated so that they do not come in line with each other. Leakage should be permitted through the gland after the packing is first installed. The gland should then be set up in small increments with several minutes between tightening in order to permit the packing to adjust itself to the shaft gradually.

c. Injection system. The injection system for each cylinder is made up of the injection pump, injection nozzle, and the tubing connecting the two units.

1. The injection pump is of the constant

The injection pumps are enclosed in the cylinder block in an inverted position on the control side of the engine below the camshaft. The camshaft is driven through a silent chain by a sprocket on the control end of the upper crankshaft. Each pump consists of a housing, plunger, barrel, control rack, plunger spring, delivery valve, delivery valve seat, and delivery valve spring. The push rod assembly transforms the rotary motion of the camshaft into linear up-and-down motion of the plunger.

The injection pump plunger moves in the plunger barrel with a constant stroke and delivers fuel through the delivery valve and injection tubing to the injection nozzle and on to the combustion space in the cylinder liners. The

When the plunger is in its highest position, the fuel inlet port is uncovered and the pump barrel fills with fuel. As the plunger moves down, the port is covered and fuel is delivered to the combustion space. Delivery of fuel continues until the helical edge of the plunger uncovers the bypass port. Fuel not required for combustion is discharged through the bypass port to the suction header. (See Figure 5-23.)

The exact position in the plunger stroke at which the helical edge uncovers the bypass port depends on the rotary position of the plunger. When the plunger is in the stop or no fuel position the vertical groove and the helical edge of the plunger keep the bypass port uncovered during the entire plunger stroke, bypassing all the fuel.

Rotary position of the plunger is controlled by the regulating governor through its linkage with the fuel control rod and injection pump control rack. The control rack is connected to the fuel control rod of the governor linkage at the shifter sleeve and to the injection pump at the plunger control sleeve. The sleeve is toothed at one end and slotted at the other end. Lugs on one end of the pump plunger fit into the slots of the control sleeve.

For an increase in fuel, the shifter sleeve moves the control rack through the shifter sleeve key. For a decrease in fuel, the control rack is moved by the control rod shifter sleeve spring. This flexible design is used to actuate the control racks so that if any of the racks sticks while the engine is running, the remaining pumps can be operated to decrease the fuel injected.

In order to cut out any individual pump while the engine is in operation, the shifter sleeve should be rotated until the slot in the sleeve can pass over the sleeve key of the fuel control rod. This will permit the movement of the individual control rack to the stop or no fuel position.

The delivery valve seats when the pressure of oil in the pump chamber is relieved. Because of the spring and the high oil pressure in the

2. The fuel injection nozzle consists primarily of a nozzle body, nozzle spring housing, needle sleeve, needle, push rod, spring, filter, shim and nozzle tip. On the down stroke of the injection pump plunger, fuel enters the injection nozzle through the injection tube and is forced through the nozzle filter. The nozzle filter removes any foreign matter which may have gone through the main filters.

The filter built into this nozzle is extremely simple. It is a close fit in the nozzle body with a clearance of .0015 in. to .0022 in. for fuel to pass from one groove to another. The longitudinal grooves are connected alternately with the annual grooves so that fuel entering the annular groove is forced through the space between the filter and the nozzle body into the annular groove connected to the opposite end of the filter. The filtered fuel is forced into the chamber through the flutes and holes, into the outside of the needle sleeve where it enters the chamber at the face of the needle seat.

The fuel under pressure acts against the face of the needle lifting it from its seat. The pressure of the oil is counteracted by the spring through the nozzle push rod. This permits the pressure of the fuel to build up to about 3000 lb. When it reaches this point, the nozzle needle opens, allowing fuel to escape through the three small holes in the nozzle tip into the combustion space of the cylinder in a fine spray. The fast action of the needle caused by the fuel, acting on the face of the needle, and the spring counteracting this pressure, insures quick opening and closing of the needle and eliminates dribbling or leaking.

12B6. Lubricating oil system. a. Description. Lubricating oil is supplied to the system under pressure to insure a continuous flow of oil to all surfaces requiring lubrication and to the pistons for cooling. The system is comprised of the attached lubricating oil pump, oil pan, strainer, oil separator, filter and cooler with the necessary valves and piping.

An oil gage connection to the gage board

The lubricating oil pump, located on the control end of the engine, draws oil from the oil pan through a strainer and discharges it through the filter and cooler to the lower and upper oil headers. Through branches from these headers, oil is supplied to each main bearing and to the thrust bearing. From the main bearings, oil passes through holes drilled in the crankshaft and through tubes swedged into the crankshaft to each crankpin bearing. Oil is then forced through the passages drilled the length of the connecting rod to the piston pin needle bearings or bronze bushing and to the piston oil pockets for cooling the pistons. An opening through the upper crankshaft lubricates the timing chain.

The cooling oil from each lower piston is discharged through the piston cooling bracket outlet pipe into the sump or oil pan. Oil from each upper piston is discharged through the piston cooling bracket outlet pipe into the upper crankcase compartment where it can drain toward either end of the engine and flow back to the engine sump.

Branches from the lower oil header supply oil to the thrust bearing, crankshaft vertical drive gears, and main bearings. The bushings of the flexible pump drive located on the control end of the lower crankshaft, receive lubrication through an opening in the lower crankshaft from the control end main bearing. The surfaces of the lower thrust bearing shell and the crankshaft flange are lubricated by openings in the bearing shell.

Connections from the upper oil header supply lubricating oil to the vertical drive gears and bearings, to the blower flexible drive wear rings, to the inner and outer blower impeller bearings, and to the injection pump tappet housing. The blower drive gears are lubricated by a splash system obtained from a special fitting that directs a spray of oil to the gears.

Fittings at the control end of the upper oil header supply lubrication to the timing chain and control mechanism. This oil drains down and also lubricates the governor drive and gears,

The camshaft and stub shaft bearings are lubricated by pipes from the upper oil header to the first bearing of each shaft. Oil enters the hollow shafts and lubricates the rest of the bearings through openings drilled radially in the camshaft.

Used oil from the bearings, tappet housing, and pistons collects in the upper crankcase compartment where it drains either toward the control end or toward the blower end of the block and flows back to the oil pan. Used oil from the blower gears and bearings collects at the bottom of the blower inner bearing plate and at the bottom of the blower end cover. An oil tube connects the blower end cover compartment to the inner bearing plate compartment allowing oil to drain from these areas to the oil pan, via the vertical drive compartment.

An oil separator is fastened inside the blower end cover and vents the crankcase of fumes.

b. Lubricating oil pump. The lubricating oil pump is attached to the pump mounting plate on the control end of the engine below the exhaust nozzle. It is of the positive displacement type, driven by a pump driveshaft through the flexible coupling. A built-in relief valve is set to operate at 60 pounds' pressure to relieve the pump when excess pressure is built up. Oil from the relief valve flows directly into the oil pan.

The pump should require very little attention except for periodic removal for inspection and the cleaning and grinding of the seat of the relief valve with the tool furnished for that purpose. When reassembling the pump, carefully adjust the valve to open at the proper pressure.

Special pullers are furnished among the tools for removing the drive gear, the timing gear, and drive coupling. Spanner wrenches are provided for removing the locknuts on the drive gear, the timing gear, and coupling.

c. Generator bearing drain pump. A small gear type drain pump, mounted on the front of the attached lubricating oil pump at one end of

d. Suction strainer. The lubricating oil suction strainer is located in the pump intake line. All oil from the oil pan passes through the strainer before entering the pump. The strainer consists of a piece of screen supported by a cylindrical shell which is fastened in the enlargement in the oil piping. This strainer should be removed and cleaned frequently to insure an adequate supply of clean oil to the pump.

12B7. Cooling system. a. General. An adequate supply of cool, clean, soft, fresh water, free of scale-forming ingredients, is essential for proper operation of the engine. The sodium dichromate water treatment should be used. Salt water should not be used for cooling the engine.

The cooling system is of the closed type in which fresh water is circulated through the engine and fresh water cooler. Salt water is circulated through the fresh water cooler and through the generator air cooling system. For more detailed discussion, the two systems are discussed separately. In older installations, salt water is used as the cooling agent in the lubricating oil cooler, but in later installations, fresh water is used.

b. Salt water system. The salt water system consists of an attached salt water pump which is driven through the flexible drive from the lower crankshaft. It draws water from the suction sea chest and strainer, forces it through the generator cooling system, the fresh water and sometimes the lubricating oil coolers, and discharges it overboard. The necessary piping, fittings, and valves complete the system. A hand-operated three-way bypass valve is installed in the discharge piping from the pump to the cooler, controlling the amount of salt water passing through the coolers and thereby, to some extent, the temperature of the fresh water and lubricating oil to the engine.

Since the salt water and fresh water pumps

c. Fresh water system. The attached fresh water pump is driven through the flexible pump drive from the lower crankshaft and draws water from the fresh water cooler and forces it into the engine at the base of the exhaust nozzle. From the exhaust nozzle, water flows around the jacketed outside of the exhaust manifold, thence through fittings into the space between the cylinder liner and jacket on each cylinder. The heat of combustion is transferred to the cooling water as it travels up and around the cylinder liner, injection nozzle, air start check valve, and cylinder relief valve. The water leaves the jacketed space of the liner by means of outlet pipes connected to the water header on the side opposite the control side of the engine. The water flows past a mercury bulb thermometer where the outlet water temperature of the engine is registered.

Adjustments are possible so that part of the water can be bypassed around the cooler by means of a temperature regulator similar to that used on the Model 38D 8 1/8 engine. All of the cooling passages of the engine can be drained at the exhaust nozzle. The system should be drained if the engine is to be left in freezing temperature with no protection.

d. Circulating water pumps. The pumps are of the centrifugal type with the water entering at the center of the impeller and being forced outward by the rotating motion of the impeller vanes to the pump discharge.

These pumps require very little servicing beyond the tightening or replacing of the packing and the oil retainer ring. The packing should be tightened occasionally to keep the gland from leaking. If it must be replaced, the special packing hook should be used to remove the old packing. The new packing should be cut to the correct length and the joints alternated so they do not come in line. The gland nut should then be tightened in small increments to allow the packing to adjust itself gradually to the shaft. The bearings of these pumps are lubricated from the gear drive case.

12B8. Air starting system. The air starting system is furnished with air from the ship's high-pressure air line or from air bottles. A reducing

Engine starting is accomplished by the action of the compressed air on the pistons in their proper firing order. The operation is identical with that described in Chapter 4 for a Model 38D 8 1/8 F-M engine. When the hand control lever of the fuel and governor control rod is moved from STOP to START position, the machined portion of the control valve plunger acts as a cam, forcing the control valve open, allowing high-pressure air to enter the engine starting air header and the air start distributor. The air chamber of the distributor housing the pilot valves is under pressure when the control valve is open. This pressure is greater than the force exerted by the valve springs and accordingly it forces the pilot valves down against the air start cam.

The cam is designed so that the pilot valves on high cam are closed and vented to the atmosphere. The pilot valves on low cam are open, allowing pilot air to enter the pilot tubing from the distributor air chamber. The rotation of the cam, which is driven through the flexible pump drive from the lower crankshaft, causes the pilot valves to open in time with the engine firing order, admitting pilot air up to the air start check valves. The action of this valve allows a full charge of air from the main engine starting air header to enter the combustion space in the cylinder liner, forcing the pistons apart and rotating the crankshafts.

When the engine begins to fire, the hand control lever is moved from START to RUN position. This raises the control valve spring to close the valve, shutting off the air to the engine header. The engine starting air header and air start distributor are vented to the atmosphere through an opening in the control valve. When the pressure is relieved on the air chamber, the valve springs raise the pilot valves free of the cam, thereby venting all pilot tubing to the atmosphere.

The control valve located in the engine header is held closed by the combined action of

The valve will require little servicing beyond its removal, and reseating of the valve seat with the tools furnished for this purpose. After the valve seat has been refaced, the valve should be lapped to make a positive seat and prevent leakage of air from the air inlet piping.

The air start distributor, located on the side opposite the control side of the engine below the exhaust manifold at the control end, is properly timed and marked at the factory. The distributor directs a flow of air into the combustion chamber of the engine in time with the engine firing order. Under normal circumstances it will not need to be timed again; however, should a new cam be installed, it must be retimed.

The air start check valve is located in the cylinder liner, at the injection nozzle level, on the side opposite the control side of the engine. It is actuated by a supply of pilot air from the air start distributor which acts against the pressure of the valve spring forcing the operating piston to open. When the piston opens, it releases a charge of air from the engine starting air header to the combustion space between the pistons in the cylinder liner, forcing the pistons apart and causing the crankshafts to rotate.

When the air start distributor shuts off the supply of pilot air to the valve, the spring closes the operating piston. The air from the engine starting air header presses against the balancing piston with greater force than it does against the check valve so that at no time is there enough pressure to open the valve.

The valve is vented to the atmosphere through two holes in the valve body. Water from the cylinder liner jacket enters the space between the check valve sleeve and the sleeve water jacket to cool the valve and valve body.

12B9. Exhaust system. The exhaust system conducts the gases from the engine combustion space through the exhaust ports to the