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(Source: Tractors and Automobiles, by V.Rodichev & G.Rodicheva, Mir Publishers, Moscow) 1. Operation of Multi-cylinder Engines The cycle of operations of four-stroke engines is completed in two turns of the crankshaft. With such an operating cycle, the crankshaft receives energy from the piston only during one half its turn when the piston moves on the power stroke. During the remaining three half turns, the crankshaft continues to revolve by inertia and, aided by the flywheel, it moves the piston on all its supplementary strokes – exhaust, intake, and compression. Therefore, the crankshaft of a singlecylinder engine operating on the four-stroke principle revolves no uniformly: it accelerates on the power stroke and decelerates on the supplementary strokes of the piston. Furthermore, the singlecylinder engine usually produces little power and features excessive vibration. For this reason, automobiles are powered by multiple-cylinder engines.
Fig.1. (a) Schematic diagram gram and (b) firing-order of a four-cylinder four-stroke engine
For a multi-cylinder engine to run uniformly, the power strokes of its pistons must be spaced rotationally at one and the same crank angle (i.e., they must occur at regular intervals, called the firing intervals). To find this angle, the duration of the engine cycle, expressed in degrees of crankshaft rotation, is divided by the number of the engine cylinders. For example, in a fourcylinder four-stroke engine, the power stroke occurs every 180˚ (720˚/ 4), i.e., every half turn of the crankshaft. The other strokes in this engine occur also every 180˚. Therefore, the crankshaft throws (or crank throws) of four-cylinder four-stroke engines are spaced at 180˚, i.e. they lie in a single plane. The crank throws of the first and fourth cylinders are arranged on one side of the crankshaft, and those of the second and third cylinders, on the opposite side. Such a shape of the crankshaft
and finally. eight power strokes occur for every two revolutions of the crankshaft. In an eight-cylinder four-stroke engine. The firing order of eight-cylinder four-stroke engines is 1-5-4-2-6-3-78 and that of six-cylinder ones. like piston strokes occur at 120-degree intervals. Multi-cylinder engines may have an in-line or a two-bank (V-type) cylinder arrangement.1).and eight-cylinder automotive engines use Vtype cylinder arrangements. In an in-line cylinder engine. In a six-cylinder four-stroke engine. in the second cylinder (Fig. When selecting a firing order for a particular engine. 1-4-2-5-3-6. since all the pistons simultaneously reach their extreme positions (two pistons reach their TDC at the same time as the other two reach BDC). Therefore. The firing order of the four-cylinder engines is usually 1-3-4-2. all the cylinders are arranged vertically in a straight line. then in the fourth cylinder. a) Fig. while in a V-type engine. With an eight-cylinder fourstroke engine.2. the cylinders are arranged in two banks set at an angle to each other. the next power stroke occurs in the third cylinder. V-type engines are more compact and less heavy than their in-line cylinder counterparts. and so the crank throws are arranged crosswise with an angle of 90˚ between them (Fig. its crank throws are spaced in pairs in three planes with an angle of 120˚ between them (Fig. This means that after the piston in the first cylinder has completed its power stroke. The order in which like piston strokes occur in the engine cylinders is known as the firing order. designers try to distribute the load on the crankshaft as uniformly as possible.1 b). Modern six.1 a).provides for even firing intervals and a good engine balance. which makes for very smooth running of the engine. Crank-throw arrangements in (a) V-6 and (b) V-8 type engines b) . Knowing the firing order of an engine. one can correctly connect the ignition wires to the spark plugs and adjust the valves. like piston strokes occur every 90˚.
THE CYLINDER-BLOCK-AND-CRANKCASE UNIT (Fig. Horizontal partition or lower deck of the cylinder block 2 divides the unit into approximately equal halves: the upper half—cylinder block 1 – and the lower half – crankcase 3. 6 – vertical partition. the unit is fabricated with inner partitions. that tightly fit into bores in the upper and lower decks of the block.1. 5 – camshaft bearing bore. Solid vertical partition 6 passing along one of the sides of the cylinder block separates push-rod.3) of most in-line cylinder engines is a one-piece box-like casting. 3 – crankcase. 4 – crankcase partitions (bulkheads). or sleeves. 1 – cylinder block.3. these structural components do have some constructional differences. Schematic diagram of the cylinderblock-and-crank-case unit of and in-line engine.2. . The main structural component of a multi-cylinder engine is the cylinder-block-and-crankcase unit. The cylinder block houses cylinder liners. Fig. but in principle they are similar in all engines. 2 – horizontal partition (lower deck). or chambers. The framework of automotive engines is formed by a number of components that are rigidly held together. the upper deck being usually referred to as the cylinder deck. Engine Framework The engine framework serves as an enclosure and a support for all the component parts of the engine mechanisms and systems. this combination generally being termed monoblock construction. or bulkheads. chamber 7 from the water (coolant) jacket. Crank Mechanism 2. To improve its rigidity and divide it into several compartments. Depending on the engine type and power output. or tappet. 7 – push-rod (tappet) chamber.
The space between the vertical partition. cylinder block walls. The cylinder block jacket communicates with the cylinder head jacket via holes 2 in the cylinder deck. (c) air-cooled engine 1 – push-rod holes. The deck is also provided with threaded holes 3 for the studs that hold the cylinder head down to the cylinder block and holes 1 for the push-rods. while detachable inverted bearing caps 6 accommodate the lower main bearing halves. Rubber sealing rings 8 grooved into the lower deck of the cylinder block serve to prevent the leakage of coolant from the cylinder block jacket into the crankcase and also to avoid crankcase oil finding its way into the cooling system. 2 – water holes. the crankshaft is underslung in the crankcase and supported by crankcase (or main bearing) bulkheads 4 that form a series of crank chambers. and cylinder liners is filled with water and forms a water jacket. 4 – water passage.4 b) accommodate cylinder liners 10 and are integrated by a common water jacket. 10 – cylinder liner (sleeve). to supply oil to some wearing component parts of the engine. Cylinder banks 11 and 13 of the cylinder-block-and-crankcase unit of a V-type engine (Fig. 3 – cylinder head stud holes. 5 – oil passage. Main bearing caps 6 are held to the bearing saddles . 8 – rubber sealing ring.4 a) formed in these bulkheads. on the side nearest the tappet chamber. In the crankcase bulkheads. With this type of construction. In the cylinder block. Fig. 6 – crankshaft (main) bearing caps. 14 – stud. there are bores 9 for camshaft bearings. 18 – sealing gasket. there are cast passages 4 intended to deliver water from the water pump into the block and drilled holes and passages 5. 7 – bearing saddle. (b) liquid-cooled V-type engine. In the center of the unit. The upper main bearing halves are carried directly in saddles 7 (Fig. 17 – crankcase. Cylinder-block-and-crank-case unit of tractor engines (a) liquid-cooled in-line engine. there are bores 9 for the camshaft bearings. 15 – air-cooled cylinder barrel. The crankcase is broadened so as to accommodate the crankshaft throws.4. 9 – camshaft bearing bore.
On the outside of any cylinder-block-and-crankcase unit. fuel injectors. the flywheel (bell) housing at the rear end. In the top deck of the crankcase. The space between the ports and the cylinder head walls is filled with water and forms what is known as water jacket. there are machined bosses and pads with threaded holes for mounting various engine units and assemblies.in the crankcase bulkheads by studs 14 and nuts. The lower deck of the head is carefully machined and forms the top wall of the combustion chambers of all the four cylinders. In some engines. the crankcase breather is mounted on the cylinder block side wall nearest the tappet chamber or in the oil filler cap. the timing case at the front end. The breather lets out combustion gases and air that have forced their way into the crankcase from the cylinders and thus prevents crankcase oil being squeezed out through the various engine seals. and the sump at the bottom. metalasbestos gasket is placed between the cylinder head and block. as is the case with liquid-cooled engines. such as gaskets or seals. To prevent the leakage of combustion gases and water. so that the leakage of coolant or oil may be prevented and dirt finding its way into the unit avoided. The cylinder barrels together with cylinder heads are held down to the crankcase deck by special studs 14 and nuts. The crankcase accommodates both the crankshaft and camshaft.4 c). Positive sealing arrangements. The openings in the gasket are edged in sheet steel where the gasket surrounds the cylinder liners and the oil passage to the valve mechanism. The cylinder heads are mounted on plane A (cylinder decks) of the cylinder banks. and push-rods and also with intake and exhaust ports. Breather fitted in the valve cover makes it possible for the crankcase to communicate with the atmosphere. copper sealing gaskets 18 being placed between the barrels and the crankcase. As distinct from liquid-cooled engines. all the engine components being carried by cast crankcase 17 (Fig. Most carburettor engines use a forced (closed) system of crankcase ventilation which ensures a more positive removal of the harmful . It also lets the atmospheric air in the crankcase if the pressure of the air cooling in the crankcase after the engine has stopped should fall below atmospheric pressure. there is no cylinder-block-and-crankcase unit in aircooled engines. Attached to the cylinder-block-andcrankcase unit are also the other structural components of the engine: the cylinder head at the top. The cylinder head is provided with openings for the valves. CYLINDER HEAD of a multi-cylinder engine is a robust iron or aluminium alloy casting resembling a thick plate that covers the cylinder block. The valve mechanism is mounted on the top deck of the cylinder head and is enclosed by the cylinder head cover and valve cover. there are bores 16 to fit cylinder barrels 15. The oil-soaked wire-mesh stuffing of the breather cleans the air entering the crankcase from dust. are used between the joint faces of the cylinder-block-andcrankcase unit and the engine components mounted on it.
Oil pan (sump) fixed to the cylinder-block-and-crankcase unit from below serves as an oil reservoir and a closure for the lower part of the engine. Cylinder liners are made of an alloy cast iron. 7 – water jacket. (c) air-cooled cylinder. a timing pointer) to locate the piston of the first cylinder at its top dead centre for timing purposes. 6 – insert. of tractor engines are usually cast in iron. is thoroughly machined and hardened. 1. since worn liners can fairly easily be renewed. The inner surface of the cylinder liner. (b) illustrating the installation of a cylinder liner in an automobile engine. except for the oil pan.blow-by combustion gases and fuel vapours from the crankcase. For passenger car engines liners are not used and cylinders are machined in the cylinder-block. Fig. 2.collar. In some engines. 8 – sealing gasket. which increases the service life of the cylinder-block-and-crankcase unit..2. called the face. THE BELL HOUSING serves to accommodate the flywheel and to mount the engine on the tractor frame. The crankcase to oil pan joint is sealed by a cork or rubberized asbestos fabric gasket. 2 – top retaining flange. each cylinder has a head of its own. cylinder liners (Fig. 9 . 5 – cylinder barrel. The structural components.5). the flywheel housing is provided with means (e.g. Cylinders (a) wet cylinder liner. In air-cooled engines. Cylinders and Pistons CYLINDERS of the automotive engines are of detachable (insertion) type. whilst those of some automobile engines use an aluminium alloy. 3 – bottom retaining flange. The external surface of the cylinder head is in this case provided with cooling fins.crankcase .5.
Each cylinder. In some engines. THE PISTONS (Fig. . these rings are grooved into the retaining flange.Cylinder liners whose outer surface is exposed to the coolant in the cylinder jacket are of what is known as the wet variety (Fig.5 a). In some engines. It consists of crown. it must be light in weight and conduct heat well. Accordingly. head (or sealing part) B.5 c) are provided with cooling fins on the outside. The cylinder liners of some automobile engines are fitted with wear-resistant inserts 6 (Fig. and thus increase its durability. The pistons of diesel engines (Fig. a metallic-bonded steel groove insert is used for the top compression ring in order to improve the wear resistance of the ring-to-groove joint. The outer surface of the piston head and skirt is provided with grooves 5 and 2 to accommodate compression and oil-control rings. referred to as the piston skirt. or top. and move with significant velocities inside the cylinders. The outer wall of the wet liner is made to have two retaining flanges 2 and 3 that provide for the liner to fit tightly in the cylinder block.5 b) of anticorrosion cast iron in order to reduce wear on the top part of the liners. while in others they are grooved into the cylinder block. there is a retaining flange that rests against the crankcase deck. but sufficiently strong aluminium alloy. In the lower part of the cylinder barrel. The amount of protrusion is usually termed the nip of the cylinder liner. respectively. together with its head. The cylinder barrels of air-cooled engines (Fig. In some engines. The number of the rings installed on a piston depends on the engine type and the crankshaft rotation frequency. Rubber sealing rings 4 installed between the lower retaining flange of the cylinder liner and the cylinder block prevent the leakage of coolant from the cylinder jacket into the crankcase.6 b) are made with recesses (cavities) in their tops. and thus creates an efficient seal against combustion gases escaping from the cylinder. and also participate in all the operations constituting the working cycle of the engine. Cylinder liners are generally fitted so that their top end face protrudes a little above the top deck of the cylinder block.6) take up and transmit to their connecting rods the forces resulting from the gas pressure in the cylinders. annular copper gasket 8 is placed between the bearing surface of the lower retaining flange of the cylinder liner and its seating in the lower deck of the cylinder block. The piston (Fig. which ensures a better compression of the metal-asbestos cylinder head gasket. is clamped to the crankcase by means of special (anchor) studs and nuts.6 a) resembles an inverted cup. their material must be adequately strong and wear-resistant. Therefore. whose shape depends on the method of mixing the fuel with air and the arrangement of the valves and fuel injectors. Oil-ring grooves have through holes drilled in their backs around the periphery of the piston to drain the oil scraped off by the rings into the engine crankcase. A copper ring is used between the flange and the deck. The pistons are exposed to high temperatures and pressures. and guiding part C. A. the pistons in modern engines are cast in a light-weight.
E . 5 .bosses. C. The piston pin bosses are joined with the piston crown by intermediate supporting webs. B . Fig. 3 . D .skirt. Pistons (a) piston of a tractor diesel engine. 7 . 6 . d) piston pin 1 .skirt relief (cooler) c) piston of an The pistons of some tractor engines are made with shallow (0. automobile SI engine.oil-scrapping edge. 8. Carburettor engines use flat-topped pistons (Fig.lock ring groove.piston pin lock ring (circlip): A .oil-ring groove. so that oil pockets – “coolers” – are formed where oil is accumulated to facilitate the cooling of the thickened part of the piston and prevents it from becoming stuck in the cylinder. or retainers. 2 .crown.6.piston head. which is both tapered in profile (the skirt diameter is greater than the head diameter) and oval in contour (the major axis of the skirt is disposed in the direction across the piston pin).oil holes to lubricate piston pin. Such pistons have found extensive .compression-ring grooves. 8 . b) cross-section through tractor engine piston.combustion chamber bowl.6 c). These grooves trap the ring carbon resulting from the burning of oil. which improve the strength of the piston.3 mm deep) annular grooves in the head (Fig.On the inside of the piston skirt. The latter end is also attained with pistons machined to a special form. The piston skirt is relieved on the outside opposite the piston pin bosses. and thus prevent premature seizure of the piston rings. Annular grooves 3 cut in the pin holes serve to accommodate piston pin lock rings.compensating slot. there are two bosses D with holes to fit the piston pin (also known as the gudgeon pin). 4 .6 b).
In some automobile engines. preferably equally spaced around the piston circumference. and they are necessarily cut through at one point. During operation of the engine. Piston rings are made of an alloy cast iron or steel. PISTON RINGS (Fig. The piston pin connects the piston with its connecting rod. Piston ring joints may be of a simple butt. The slots increase the flexibility of the piston skirt. Such a piston pin is known as the fully floating type.6 d) are hollow and are made of steel. for they are fairly simple to manufacture and run colder than other piston types. as the normal running temperature is reached. or circlips. PISTON PINS (Fig. and their skirt may incorporate a near vertical or a T-shaped compensating slot. The piston pin is kept from axial movement by internal spring lock rings. they are installed in the engine so that the side thrust arising from the connecting rod angularity on the power stroke is taken by the solid part of the piston. and so the pin becomes free to turn in the piston bosses. the rings are classed into compression rings 1 and oil-control rings 2. where combustion pressures are . while the oil-control rings prevent the crankcase oil from getting into the combustion chamber. The outside diameter of the rings is greater than the cylinder bore. The compression rings maintain an effective seal against combustion gases leaking past the piston into the crankcase.7) create a gas-tight sliding seal between the piston and cylinder. or seal-cut type. whereas in diesel engines. 8 that are expanded into grooves in the piston pin bosses. so that they may be installed in their grooves in the piston and are free to exert an initial pressure against the cylinder wall and tightly fit it when compressed into the cylinder. Two or three compression rings are enough to provide an effective combustion chamber seal in carburettor engines. According to purpose. scraping all oil surpluses to that required for proper lubrication of the piston and cylinder combination of the cylinder wall. Where the pistons have split skirts. To lessen the leakage of combustion gases through the gaps in the piston ring joints. for they are the most simple and the least costly to manufacture. The assembly fits are normally such that the pin has a clearance in the connecting rod small end bush and interference in the piston bosses. The pistons have part-circumferential compensating slots 7 beneath the head. the rings are installed on the piston so that their joints are on the opposite sides of the piston. a clearance appears in the piston boss-to-pin joints because of the different linear expansion coefficients of the piston and pin materials. The cut in the piston ring is termed the piston ring joint. bevel (tapered). the piston skirt is partially cut away below the piston pin group bosses in order to provide for the free passage of the crankshaft counterweights past the piston at BDC and to reduce the weight of the piston. termed simply the ring gaps.application. Butt joint piston rings are the most common type used in automotive engines. which eliminates the danger of the piston seizure in the cylinder.
or bevel.piston Compression rings may have various crosssectional shapes (Fig. known as the twist-type (torsional) piston rings. such rings tend to deform (twist) and put their sharp bottom edge against the cylinder face.oil-control ring. . 1 . a) Outside view. is attended by a loss of engine power and an increased oil consumption. they move less in the axial direction relative to the piston. and the rings will stop moving freely in their grooves and exerting the necessary pressure against the cylinder walls. taperfaced. When compressed into the cylinder. In some engines. If the rings poorly fit the cylinder walls. Piston rings are assembled in their grooves so that they have a small clearance and are free to move relative to the piston. 3 .7. Piston rings. operate similar to the taper-faced rings. A trapezoidal cross-sectional shape of piston rings (rings of such section are known as the keystone type) lessens the possibility of the rings sticking in their grooves in the case of heavy carbonization and improves the contact between the rings and the cylinder walls. c) composite oil-control ring.higher.flat steel rings (rails). The resulting carbon deposits will fill the piston ring side clearances. combustion gases will leak through gaps between the rings and the cylinder face and cause the rings to overheat. these rings. 5 radial spring expander. of piston rings. compression rings have their inner upper corner chamfered or counterbored. known as the seizure or sticking. This phenomenon.axial spring expander. d) arrangement of rings on a piston. 6 . 4 . which ensures their quick bedding in to and good contact with the cylinder face over its entire periphery.compression ring. Therefore. three or four such rings are commonly used on a piston. 2 . As compared with the rings of plain rectangular section. Fig. b) cross-sectional shapes of compression rings in working position. but at the same time.7 b). rings have a smaller contact area.
the connecting rod is subjected to both gas pressure and inertia loads. whereas the radial-type expander is a polygonal shape spring strip which is compressed between the inner edges of the rails and the back of the groove to press the rails radially against the cylinder face. The connecting rod small end is made in the form of a continuous eye into which bronze bush 2 is pressed so as to provide an interference fit.The working face of the top compression ring is chromium plated in order to extend the useful life of all the piston rings and the cylinder liner. starting with the first rod from the radiator. The nuts on the connecting rod bolts are tightened with a torque indicating wrench and then cottered. these rings either have through slots machined in them radially or consist of two scraper-type rings.7 c) comprising two flat steel rings. Shank. To avoid misplacing the rod caps during assembly. The axial expander is a wave form spring compressed between the rails to press them against the sides of the ring groove. whereas the big end of the rod is split into two halves with the upper half integral with the rod shank and the lower half in the form of detachable cap 6. 2. Connecting Rods and Crankshaft THE CONNECTING RODS (Fig. Therefore. the rod caps must not be interchanged. The composite-type oil-control rings tightly fit the cylinder walls and provide for low oil consumption. it must be adequately strong and rigid and light in weight as well.3.8 a) link the pistons with the crankshaft and transmit to it the loads arising from the combustion gas pressure taken by the pistons. The connecting rod big end houses a sliding contact bearing comprising two half-liners. the connecting rods and their mating caps are marked on one side with serial numbers. 3 of the connecting rod is provided with an I-cross section to give the rod maximum rigidity with the minimum of weight. Connecting rods are generally fabricated from high-quality steel in the form of a bar with ring-shaped heads at its ends. Many engines have their piston rings tinned to improve their bedding-in conditions. the heads being known as the connecting rod big end and small end and serving to attach the rod to the crankpin and the gudgeon pin of the piston. and two spring expanders – one axial and the other radial type. to identify their location in the engine. Both halves of the connecting rod big end are joined by means of special high-strength bolts 10 and nuts. In operation. The oil-control rings (one or two such rings may be used on a piston) are installed below the compression rings. In contrast to the latter. respectively. or . Some engines use composite oil-control rings (Fig. or blade. The bore in the connecting rod big end is machined after the cap is assembled on the rod. and therefore. called rails.
connecting rod bolt. The half-liners are kept from shifting endwise or rotating by locating lugs or locking lips.inserts. 9 that nestle in special slots provided in the housing on one side of the rod. 4 .connecting rod bush.oil passage.connecting rod small end.oil hole.connecting rod cap.serrated joint. The oil necessary to lubricate the piston pin is supplied either through oil hole 11 (Fig.connecting rod big end. 7 . 9 locating lug. 5 . 14 . Connecting rods (a) connecting rod components.tab washer The parting line between the connecting rod and its cap is generally arranged at right angle to the axis of the shank. 5. 2 . the cap is secured to the connecting rod by setscrews instead of bolts and nuts.8c). (d) methods of locating connecting rod cap. 8 horned nut. 13 . (c) angled connecting rod big end. Fig. 10 . 11 . the parting line is necessarily arranged diagonally. but in some engines.connecting rod shank (blade).8. 6 . With such an angled big end (Fig.connecting rod bearing half-liner (insert).8 b) or via oil passage 12 drilled through the connecting rod shank. To resist the greater tendency for the inertia forces to displace the cap sideways relative to the connecting . 12 .cotter pin. 1 . 3 . The connecting rod big end of automobile engines features a hole through which oil is squirted onto the cylinder walls. (b) cross-sections through connecting rod shanks (blades) and methods of feeding oil to piston pin. because the proportions of the connecting rod big end are such that the lower part of the rod could not otherwise be passed through the cylinder for assembly purposes.
9.web (cheek). it also drives various engine mechanisms and components. 18 . Hence. The crankshaft therefore must be adequately strong and wear-resistant. 19 . 8 . 9 .rod.oil pump drive gear.main bearing saddle insert. 6 . 17 .crankpin. 13 . 16 .dowel. THE CRANKSHAFT (Fig. 7 . 2 . 14 .bolt. 4 . 11 . The periodic gas pressure and inertia forces taken by the crankshaft may cause it to suffer wear and bending and torsional strains. Tab washers 14 (Fig.main bearing cum insert. 12 .screw plug.crankshaft flange. the retaining setscrews in their clearance holes are completely relieved of shear loads.fan drive pulley. 3 .9) takes the downward thrusts of the pistons and connecting rods when the fuel-air mixture is burned in the cylinders and changes these thrusts into torque which is transferred to the drive line of the tractor or automobile.flywheel bolt.oil slinger. 10 . Fig.flywheel ring gear. (b) of V-type engine 1 . either a serrated or a stepped joint is generally preferred for their abutting faces.8 d) are used under the heads of setscrews in order to prevent the latter from working loose.crankshaft gear.counterbalance weights.clean oil outlet tube. 15 .thrust half washers. 5 flywheel.main bearing journal. Crankshafts (a) of in-line engine. .
The main bearings. like the crankpin bearings. The crankshaft front end carries one or two gears for driving the valve mechanism and also other engine mechanisms. the half-liners are tinned on the inside. The open ends (or end where angular blind holes are necessary to clear counterbalance weights) are sealed by screw plugs 17. mechanical impurities (wear products) contained in the oil inside the hollow crankpins settle on the crankpin interior walls under the action of centrifugal forces. In some engines. and a shank (rear end). fan drive pulley 16. each crankpin has two connecting rods assembled on it. 4 and 10 made of a steel-aluminium bimetal band comprising a steel backing to which is bonded a thin layer of an antifriction alloy capable of withstanding heavy loads and possessing a high wear resistance. The main bearing journals and crankpins are induction hardened to improve their wear resistance. The endwise movement of the crankshaft in some engines is restricted by similar thrust bearing arrangements embracing either the front or one of the intermediate main hearing journals. For this purpose. take the form of half-liners. In front of the flange. Other engines have their crankshafts provided with flange 19 in which holes are drilled for securing the flywheel. in conjunction with a close clearance plain bore housing. since the hollow interior C of each crankpin also acts as an oil supply duct for big-end lubrication and as a centrifugal oil cleaner. a nose (front end). It consists of main bearing journals 1. Drilled diagonally through the crank webs are oil holes to supply oil to the crankpins. The half-liners of both the crankpin bearings and most of the main bearings are interchangeable. With the crankshaft rotating. 2 that connect the journals and crankpins together. Counterbalance weights 12 necessary for balancing the crankshaft are either formed integrally with. webs. the crankshaft is provided with an oil-return thread which. In V-type engines. and therefore. The crankpins are bored hollow in order to reduce the crankshaft inertia. forms a labyrinth-type seal operating upon the Archimedean screw pump principle to oppose the leakage of oil into the bell housing. or attached separately to. crankpins 11. and a starting crank jaw (ratchet) or bolt 15. the crank webs. Attached to the rear end of crankshaft is flywheel 5. To improve their embeddability. The rear end of the crankshaft usually carries a thrust collar which serves to prevent the shaft from moving endwise. or cheeks. In some engines. THE FLYWHEEL contributes to the uniform rotation of the crankshaft and helps the engine . the flywheel is located relative to the crankshaft by dowels 7 and clamped firmly to the rear face of the shaft by a ring of bolts 8 screwing direct into the shaft end. the crankshaft gear is carried on the rear end of the shaft.The crankshaft is either forged from high-quality steel or cast in a high-strength iron. or inserts. the rear main bearing is provided either with integral flanges on both its sides to serve as thrust faces or with separate semicircular thrust washers 3. the crankpins here are longer than in in-line cylinder engines. Mounted between the crankshaft pulley and gear is oil slinger 6 that throws oil away from the crankshaft front bearing seal.
the flywheel rim is ring gear 9 which serves to impart rotation to the crankshaft from a starting device or a starter motor when starting the engine. the piston is at TDC. In the front face of the flywheel. its rear face is thoroughly machined. Since the flywheel also serves to form part of the clutch. In some engines. The flywheel is a heavy disc of cast iron. . there is a shallow indentation used to determine the position of the piston in the first cylinder. this indentation indicates the start of fuel injection into the first cylinder. When this indentation is aligned with a special hole provided in the bell housing. The flywheel marks and indentation are used for setting the valve and ignition systems relative to prescribed positions of the crankshaft.overcome increased loads when starting the tractor from rest and also during operation. Pressed on. or bolted to.
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