| Chapter two
MOTORCYCLE POWER PLANT The power plant of a motorcycle includes the engine and the lubrication, power and ignition systems that serve it. The motorcycles of the Kyiv Motorcycle Plant are equipped with two models of four-stroke carburetor engines: K-750 with a side-bottom valve arrangement (for models K-750M, MV-750, MV-750M) and MT-801 with an overhead valve arrangement (for motorcycles K-650, MT-9, MV-650). The design of the K-750 and MT-801 engines is discussed sequentially in the book. ENGINE K-750 Engine K-750, longitudinal and transverse sections of which are shown in Fig. 6 (see incl.), two-cylinder, four-stroke, lower valve, air-cooled, with cylinders arranged horizontally (at an angle of 180°), with a displacement of 746 cm3, is a road-type motorcycle engine. The engine consists of a crank mechanism, gas distribution mechanisms, crankcase ventilation and a lubrication system. The crankcase contains a 6-volt DC electric generator, a distributor chopper and an ignition coil. crank mechanism The crank mechanism converts the linear, reciprocating movement of the pistons into the rotational movement of the crankshaft. This mechanism consists of a crankshaft 28 (Fig. 6), connecting rods 23, pistons 18 and cylinders 3 mounted on the crankcase 47. The crankshaft is installed inside the crankcase on ball bearings 69 and 70. Above it is the camshaft 33. Cylinders 3 are attached to the sides of the crankcase on studs. At the front, the crankcase has a blank wall with slots for bearings, and at the back it is closed by a round housing cover 49 for the rear crankshaft bearing. At the rear of the crankcase there is a flywheel chamber 30, which is a connecting link with the gearbox housing. In the front part of the crankcase there is a chamber in which there are gas distribution gears 39 and 43 and a generator drive gear 37. This chamber is closed with a cast lid 36. At the top of the crankcase there is a boss on which a generator 35 is installed, secured with a clamp 6. From below, the crankcase cavity is closed with a ribbed stamped pan 55 with a cork gasket 48. To attach the crankcase to the motorcycle frame, it has two through holes a and b. An aluminum spacer tube with rubber O-rings is pressed into hole b to prevent the oil in the crankcase from leaking out. Oil is poured through the filler hole, closed with a 6O plug with a dipstick, and goes down through the hole in the sump 55, closed with a plug 52. At the bottom of the crankcase there is a boss with a machined plane for installing an oil pump that supplies lubricant to the crankshaft shafts, the left cylinder and the distribution gears through the oil line channels. The engine crankshaft (Fig. 7) consists of two axles 1 and 6 with journals for support ball bearings, a cheek 2, two fingers 11 and oil traps 5 and 13. The shaft parts are connected by a press fit with the elbows mutually positioned at an angle of 180°. The fingers 11 have cavities and radial channels for supplying lubricant to the connecting rod roller bearings. The connecting rods together with the crankshaft form an integral structure, since they cannot be removed without unpressing the crankshaft. In the lower heads of the connecting rods there are single-row roller bearings 7 with cages. The outer ring of the roller bearing is the hardened surface of the connecting rod head, and the inner ring is the surfaces of the fingers 11. Bronze bushings 9 are pressed into the upper heads of the connecting rods. A timing drive gear is installed on the journal of the front journal of the crankshaft, and a flywheel 30 is installed on the conical shank of the rear journal (Fig. 6). The pistons of the K-750 engine (Fig. 8) are cast from a special aluminum alloy with minimal volumetric expansion when heated. The main parts of the piston are the bottom a, skirt b and bosses, made in the form of bosses inside the piston and reinforced with ribs connecting them to the bottom. On the surface of the piston at the bottom there are four annular grooves: the upper one is thermally insulating, serves to remove heat and prevent burning of the piston rings, two grooves d - for installing compression rings 2 and groove e - for installing the oil scraper ring 3. A similar groove for the second oil scraper ring located in the lower part of the piston skirt. Two oil scraper rings, which discharge excess oil from the cylinder surface into the crankcase through holes located along the perimeter of the grooves, significantly reduce engine oil consumption. The piston rings are made of gray cast iron, subjected to special heat treatment, ensuring the elasticity of the rings in the range of 2.9-4.3 kgf for compression rings and 2.3-4.3 kgf for oil rings. The locks in the rings are straight, with a gap in the free state in the range of 9-13 mm, and in the working position in the cylinder 0.25-0.5 mm. To avoid gas breakthrough, the ring locks must be offset during installation. The pistons are connected to the upper heads of the connecting rods using steel, hardened and polished on the outer surface of the piston pins 4. From axial movement, the piston pin is secured by two spring retaining rings 5 installed in the annular grooves of the piston bosses. The K-750 engine cylinders, having the same design, differ in the placement of the intake and exhaust valves and are therefore not interchangeable. They are cast from special alloy cast iron and have a carefully machined and polished working surface. The outer surface of the cylinders has fins for cooling. Channels are cast in the cylinder body for intake of the working mixture and exhaust gases. The channel openings at the outer ends of the cylinders are closed by valves installed in the guide holes extending into the cavities of the valve boxes cast integrally with the cylinder flanges. The cylinder flange is attached to the engine crankcase with six studs, and the part of the cylinder protruding beyond the plane of the flange fits inside the crankcase, centering the cylinder in the mounting hole. The outer plane of the cylinder is carefully machined to connect to the cylinder head and has eight threaded holes. The left engine cylinder has an annular inlet on the flange plane with three holes extending onto the working surface of the cylinder to supply lubricant to the cylinder mirror from the oil line. The mirror of the right cylinder does not have a lubricant supply and is lubricated by splashing. The cylinder head is cast from aluminum alloy and has fins for better heat dissipation. A shaped combustion chamber is cast inside the head, in the upper part of which there is a threaded hole for a spark plug. The head is secured to the outer plane of the cylinder with eight bolts. An alloy shaped gasket is placed between the end of the head and the outer plane of the cylinder. Engine crankcase ventilation mechanism During engine operation, part of the working mixture and exhaust gases, penetrating into the crankcase through the gaps of the piston rings, creates increased pressure in it. Therefore, at certain moments the crankcase cavity must be connected to the atmosphere to release accumulated gases, while at the same time maintaining its tightness from the absorption of dust and moisture from the outside. For this purpose, the K-750 engine is equipped with a crankcase ventilation mechanism (Fig. 9) of a mechanical type. It consists of a hollow cylindrical breather 3 connected by a driver 2 to the gear 1 of the camshaft 4 of the engine. The cylindrical part of the breather rotates simultaneously with gear 1 in the socket of the cover 8 and has two holes 10 at an angle of 180°, which after half a turn coincide with the tube 7 brought out through the body of the cover 8. Gases from the crankcase enter the breather cavity through radial holes 11 drilled in the breather flange, and when hole 10 coincides with the outlet channel of tube 7, they are thrown out. For two revolutions of the engine crankshaft, the breather, making one revolution, twice connects the crankcase cavity with the atmosphere precisely at the moment the pistons converge and the pressure in the crankcase increases. The opening and closing phase of the breather is selected so that when the engine is running, the pressure in the crankcase is maintained at 0.04-0.06 kgf/cm2 below atmospheric pressure, preventing oil from leaking through the crankcase seals. Gas distribution mechanism The gas distribution mechanism regulates the engine's operating processes by injecting the working mixture into the cylinders and releasing exhaust gases into the atmosphere after combustion of the mixture at certain intervals. 
Rice. 10. Gas distribution mechanism of the K-750 engine: 1 – valve box cover; 2 – camshaft; 3 – camshaft gear; 4 – breather leash; 5 – breather; 6 – camshaft flange; 7 – camshaft oil seal; 8 – camshaft exhaust cam; 9 – pusher; 10 – pusher guide; 11 – lock nut; 12 – pusher adjusting bolt; 13 – lower valve spring plate; 14 – cracker; 15 – valve spring; 16 – exhaust pipe; 17 – upper valve spring plate; 18 – exhaust valve; 19 – heat-insulating gasket; 20 – inlet valve; 21 – inlet pipe; 22 – camshaft spiral gear; 23 – bushing of the rear camshaft bearing; 24 – oil pump drive gear; 25 – valve box cover gasket The gas distribution mechanism consists of a camshaft 2 (Fig. 10), pushers 9 with adjusting bolts 12, pusher guide bushings, an exhaust valve 18 and an intake valve 20 with springs 15 and support plates 13 and 17, and a pair of timing gears. Drive gear 1 (Fig. 11) of the gas distribution is installed on the engine crankshaft, and driven gear 10 is installed on the camshaft journal. The camshaft is mounted in the engine crankcase on two supports: a ball bearing installed in the hole in the front wall of the crankcase and held from mixing by flange 6 (Fig. 10), secured with two screws to the wall, and a bronze bushing 23 pressed into the rear wall of the crankcase. The camshaft has four profiled cams, the first and second of which serve to lift the exhaust valves of the left and right cylinders, and the third and fourth, respectively, for the intake valves (counting from the timing gear side). The profile of all four cams is the same, but each cam is shifted by an angle corresponding to the valve timing. At the rear end of the camshaft, a helical spur gear is milled, driving gear 24 of the oil pump drive. At the front end of the camshaft there is a profile cam for opening the contacts of the breaker-distributor. Valves 20 and 18 are designed to close the intake and exhaust valves of the cylinders. Each valve consists of a stem and a head, which are the same size and shape for all valves. There is an annular chamfer on the bottom of the valve head, ground at an angle of 45° along the chamfer of the seat located on the cylinder. At the end of the valve stem there is an annular groove into which split conical crackers 4 are inserted (Fig. 12), holding plate 3 of the valve spring 2. Valve springs serve to return the valves to their original position after they are lifted by the camshaft cam. They are installed with a pre-compression of up to 38 kgf to ensure proper elasticity. To prevent overheating of the springs during engine operation, thermal insulating cork gaskets are installed in the valve chambers of the cylinders under the support plates 12. Pushers 7 communicate movement to the valves from the camshaft cams, ensuring their lift by 6.9 mm according to the height of the cams. The pushers are made in the form of cast iron cylindrical rods with a rectangular head, on the working surface of which, which is in contact with the camshaft cam, there is a bleached layer of high hardness. At the cylindrical end of the pusher rod there is a threaded hole into which the adjusting bolt 11 with lock nut 5 is screwed. The pushers have aluminum guides 6, installed in the crankcase holes and secured with conical strips. The guides have longitudinal grooves in which the lateral planes of the pusher heads slide. The axes of the valves and pushers are located at a certain angle and are mutually offset to ensure rotation of the valves relative to their axis during operation, thereby reducing wear and maintaining the tightness of the working surfaces. For normal engine operation, the clearance between the valve and the pusher is set when the engine is cold and is 0.1 mm for the exhaust valve and 0.07 mm for the intake valve. The gap is adjusted by rotating the pusher bolt to the required amount and checking with a special feeler gauge from the motorcycle spare parts, after which the adjusting bolt is fixed with locknut 5. The full cycle of working processes in the engine cylinder occurs in two revolutions of the crankshaft, and the working processes in the left and right cylinders are shifted relative to each other at 360°. Operating order of the K-750 engine The operating order of the engine and the duration of each stroke are ensured by the gas distribution mechanism. The engine valve timing diagram in degrees x crankshaft rotation angle is shown in Fig. 13. For better filling of the cylinder with the working mixture and good cleaning of the combustion chamber from exhaust gases, the inlet valve of the cylinder opens 76° before TDC. and closes 92° after the piston passes the b.m.t. Thus, the total opening time of the valve corresponds to an angle of 348°. The exhaust valve accordingly opens 116° BC. and closes 52° after the piston passes the T.M.T. The total opening time of the exhaust valve also corresponds to an angle of 348°. The valve opening time, during which the combustion chamber is ventilated, corresponds to an angle of 128°. The entire work cycle takes place in four strokes: the intake stroke, the compression stroke, the expansion stroke (power stroke) and the exhaust stroke. The intake stroke begins 76° before TDC. From the beginning of the rise of the intake valve, the working mixture enters the combustion chamber and blows it through the still open exhaust valve. Having passed the T.M.T., the piston changes direction, the exhaust valve closes and the working mixture is intensively sucked into the cylinder until the intake valve closes (92° after T.M.T.). Compression stroke. Both valves are closed. The piston moves towards the top half, compressing the working mixture. Expansion stroke (power stroke). Both valves are closed. The working mixture is ignited by the spark plug (30±2° before TDC, depending on the ignition setting) and, turning into gas, presses with force on the piston moving towards the top. m.t., and through the connecting rod rotates the engine crankshaft. The release stroke begins at 116° BC. m.t. from the moment the exhaust valve opens, through which the exhaust gases rush out. The release continues until the exhaust valve closes (up to 52° after TDC). Engine cooling K-750 air-cooled engine. The hottest parts of the engine are the cylinders and heads, which are moved to the sides and blown by a counter flow of air. To ensure intense heat transfer, the surfaces of the cylinders and heads are equipped with cooling fins. There are also ribs in the lower part of the crankcase. The crankcases and heads made of aluminum alloy also promote intensive heat dissipation, providing a total of normal engine thermal conditions under various conditions. Given the importance of ensuring normal engine cooling, it is necessary to monitor the cleanliness of the surfaces of the cylinders, heads and crankcase, cleaning their surfaces and intercostal spaces. Lubrication system For normal engine operation, it is necessary to have an oil film on all its rubbing surfaces, created by the engine lubrication system (Fig. 14). The K-750 engine uses a combined lubrication system. It allows some parts to be lubricated with oil under pressure, and some - by splashing and oil mist formed in the crankcase when the engine crankshaft rotates. The gear oil pump is installed in the lower part of the engine crankcase and, as mentioned above, is driven by the spiral spur gear 20 of the camshaft. Pump housing 1 is attached to the crankcase boss plane with two bolts and is closed from below with a flat cover with a hole through which oil is sucked in from reservoir 5. A strainer 4 is installed on the cylindrical protrusions of the cover mounting bolts, covering the oil pump housing and performing coarse filtration of the oil sucked in by the pump from engine crankcase.
Rice. 14. Lubrication diagram for the K-750 engine: 1 – oil pump housing; 2 – drive gear; 3 – driven gear; 4 – oil pump filter; 5 – oil reservoir; 6 – filter (mesh); 7 – crank pin; 8 – oil catcher; 9 – oil pocket; 10 – oil channel; 11 – connecting rod; 12 – drilling in the valve box; 13 – drilling in the left cylinder; 14 – piston oil scraper ring; 15 – hole for lubrication of the piston pin; 16 – filler plug; 17 – oil channel; 18 – oil pump housing gasket; 19 – drain plug; 20 – drive gear; 21 – oil pump drive gear; 22 – drive gear coupling; 23 – oil pump outlet; 24 – oil channel to the rear bearing; 25 – oil drain channel; 26 – crank seal; 27 – rear bearing housing; 28 – oil pump inlet; 28 – oil pump inlet; 29 – radial hole in the crank pin; 30 – rear support ball bearing of the crankshaft; 31 – recess for lubrication of the oil pump drive gear; 32 – oil pipe; 33 – front support ball bearing; 34 – recess in the bearing housing; 35 – oil pipe; 36 – drain hole; 37 – main oil line; 38 – oil channel of the front bearing; 39 – annular groove; 40 – recess for oil injection Oil from the pump body, pumped by spur gears 2 and 3, enters the oil line pipe through outlet 23, which is connected to two vertical channels 24 and 38, supplying it under pressure to oil traps 8 of the engine crankshaft. Under the influence of the centrifugal force of rotation, solid particles are discarded from the oil in the oil catchers, and the purified oil enters the roller bearings of the lower connecting rod heads through holes in the crankshaft pins and radial drillings. In this case, excess oil is thrown into the internal cavity of the crankcase and sprayed onto the surfaces of the cams and pushers of the gas distribution mechanism and onto the working surfaces of the cylinders, lubricating the bottom of the left and top of the right cylinder mirrors. In the right cylinder, oil from the upper part of the mirror lubricates the lower part by gravity, and in the left cylinder, additional oil is supplied to lubricate the upper part of the mirror. Directly from the oil line through inclined channel 17, oil under pressure is supplied to the annular groove under the flange of the left cylinder, and from there through three holes it flows to the upper part of the mirror. Part of the oil supplied through a vertical channel to the front crankshaft oil trap, through the annular groove 39 under the front bearing housing and tube 32, flows onto the surface of the teeth of the drive distribution gear and, when rotating, lubricates the teeth of the camshaft driven gear and the generator drive gear. The oil mist generated during the rotation of the timing gears settles on the friction surfaces of the front camshaft bearing and breather and ensures their lubrication. Excess oil flows down and returns through the hole to the engine crankcase. The oil mist lubricates the pushers and their guides, from where the settled oil particles penetrate into the chambers of the valve boxes of the cylinders, lubricating the rubbing surfaces of the pushers, springs and valve stems. Excess oil flows from the valve boxes into the crankcase through drilling 12. Lubrication of the piston pins and piston boss holes is ensured by the penetration of oil mist through holes 15 in the connecting rod heads. Lubrication of the rear bearing of the gas camshaft is provided by oil flowing from the walls and entering channel 10. Fresh oil is added to the engine lubrication system through a filling hole closed by a plug 16 with a dipstick, on which marks are marked indicating the maximum and minimum permissible oil level, and the drain used oil - from the system through the drain hole of the pan, closed with plug 19. ENGINE MT-801 Compared to the K-750 engine, the MT-801 engine is a further development of the four-stroke air-cooled carburetor engine for heavy-duty motorcycles and has higher technical performance. The main and significant design differences between the MT-801 engine and the K-750 engine are the use of an overhead valve timing mechanism and the installation of a cast crankshaft made of high-strength cast iron with detachable lower connecting rod heads, with replaceable automotive-type connecting rod bearing shells. The general layout of the MT-801 engine is the same as the K-750 engine with an opposed cylinder arrangement in a horizontal plane. The MT-801 engine, intended for installation on the K-650 and MT-9 motorcycles, has a 6-volt ignition system, and the engine installed on the MV-650 and the new MT-10 motorcycles has a 12-volt ignition system. Accordingly, the crankcase is provided with a flange mounting of the 12-volt generator G-424 instead of mounting the 6-volt generator G-414. The remaining ignition devices (ignition coil, breaker) in 6- and 12-volt versions are basically the same. The factory designation of the engine with 12-volt electrical equipment is KMZ.8.152.01. The MT-801 engine consists of a crank mechanism, gas distribution and crankcase ventilation mechanisms, a lubrication system, a power supply and exhaust system, and an ignition system. 
Rice. 15. Engine MT-801 (view from the front cover): 1 – left rocker arm; 2 – bushing; 3 – adjusting bolt; 4 – rod; 5 – cylinder mounting pin; 6 – rod casing; 7 – piston pin; 8 – bushing of the upper head of the connecting rod; 9 – piston; 10 – compression rings; 11 – oil scraper rings; 12 – connecting rod; 13 – cylinder; 14 – sealing cap; 15 – pusher; 16 – generator; 17 – camshaft; 18 – front camshaft bearing; 19 – generator gear; 20 – camshaft gear; 21 – breather; 22 – breather leash; 23 – breaker-distributor; 24 – drive distribution gear; 25 – front crankshaft bearing; 26 – front bearing housing; 27 – centrifuge cover; 28 – centrifuge screen; 29 – centrifuge body; 30 – oil pump gear; 31 – oil pump housing; 32 – oil receiver; 33 – pressure reducing valve; 34 – connecting rod liner; 35 – crankshaft; 36 – drainage tube; 37 – piston pin retaining ring; 38 – valve seat; 39 – lower plate; 40 – outer valve spring; 41 – internal valve spring; 42 – valve sleeve; 43 – upper plate; 44 – valve; 45 – cracker; 46 – right rocker arm; 47 – emergency oil pressure sensor crank mechanism The crank mechanism includes the engine crankcase, crankshaft with flywheel, connecting rods assemblies, piston with piston rings and pin, cylinders and cylinder heads. The engine crankcase (Fig. 15 and 16) is cast from silumin. To increase rigidity, the crankcase is made in one piece, without a split along the axis of the crankshaft main bearings. The crank and gas distribution mechanisms of the engine are located in the crankcase cavity between the front and rear walls. Behind the rear wall are the flywheel chamber and clutch. The front crankshaft bearing housing and the distribution box cover are installed on the machined front wall of the crankcase. The gearbox housing is attached to the end of the flywheel chamber on studs. In the upper part of the front wall of the crankcase there is a boring socket for installing the generator. On the side walls of the crankcase there are bosses (flanges) with threaded holes for anchor pins for fastening the engine cylinders. At the bottom of the crankcase there is a horizontal partition on which there is a boss with a through hole for the front pin mounting the engine to the motorcycle frame. The silver-plated base of the crankcase serves as an oil reservoir and is closed from below with a stamped pan. To prevent oil leakage, a soft sealing gasket made of cork is placed at the joint between the crankcase and the sump. On the base of the crankcase, two bosses are cast with a hole for the rear stud mounting the engine to the motorcycle frame.
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Rice. 16. Engine MT-801 (view from the flywheel):1 - spark plug; 2 - engine crankcase; 3 - distribution box cover; 4 - front crankcase cover; 5 - rear crankshaft bearing; 6 - rear camshaft bearing; 7 - screw securing the clutch thrust disc; 8 - clutch thrust disc; 9 - flywheel; 10 - crankshaft oil seal; 11 - oil deflector washer; 12 - spacer washer; 13 - pressure drive clutch disc; 14 - flywheel mounting bolt; 15 - driven clutch discs; 16 - clutch spring; 17 - intermediate drive clutch disc; 18 - pallet gasket; 19 - pallet; 20 - left cylinder head; 21 - cylinder head cover; 22 - blind head cover fastening nut
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The distance between the axes of the holes for the mounting studs for the MT-801 engine is the same as for the K-750 engine (193 mm). The oil fill hole is located on the left wall of the crankcase. The oil drain hole is located in a stamped pan and is closed with a threaded plug with a soft aluminum gasket. The crankshaft is solid cast from high-strength cast iron grade VCh 50-2, has two cranks located in the same plane at an angle of 180°. A centrifuge and a timing gear are installed on the front axle of the crankshaft, and a flywheel is installed on the conical part of the rear axle. The connecting rod journals have barrel-shaped cavities closed with threaded plugs. These cavities are designed for centrifugal cleaning of oil from solid inclusions. The mass of the crankshaft counterweights is selected in such a way that the moment from the centrifugal forces developed during rotation of the crankshaft balances the moment from the action of the centrifugal forces of the connecting rod journals and the related masses of the lower connecting rod heads. This ensures that the main bearings are unloaded from the inertia forces of the rotating masses. The crankshaft is installed in the engine crankcase on two bearings - ball and roller. The front ball bearing is pressed into housing 26 (Fig. 15), the flange of which is attached to the front wall of the crankcase using eight bolts. The front ball bearing absorbs axial forces and protects the crankshaft from axial displacements. The roller bearing allows some axial movement of the crankshaft rear journal. This is necessary to compensate for the difference between the thermal expansion values of the cast iron crankshaft and the aluminum crankcase in the axial direction. The use of a cast iron shaft, the connecting rod journals of which have higher wear resistance compared to steel, in combination with thin-walled anti-friction connecting rod bearing shells, ensures increased service life of the crankshaft of the MT-801 engine. Connecting rods 2 (Fig. 17) of the MT-801 engine are asymmetrical. Their I-section rods are offset relative to the longitudinal axis of the lower head, which reduces the distance between the axes of the cylinders also reduces the length of the engine. There are marks (protrusions) on the connecting rod rods. When installing connecting rods, the marks on the rods should be directed outward relative to the middle cheek of the crankshaft - towards the centrifuge for the left connecting rod and towards the flywheel for the right one. A bushing 3 made of bronze tape is pressed into the upper head of the connecting rod and flared at the ends. To ensure optimal clearance between the bushing and piston pin within 0.0045-0.0095 mm, after processing the bushings are sorted by hole into four groups and marked with paint. To lubricate the piston pin, two holes are drilled in the upper head of the connecting rod. The lower head of the connecting rod is detachable, with thin-walled interchangeable liners 4. The cover 5 of the lower head is secured with two connecting rod bolts 6 with slotted nuts. The connecting rod bolts are secured against turning by special flats on the heads. Fixation of the cover relative to the lower head of the connecting rod is ensured by ground surfaces on the rods of the connecting rod bolts. The connecting rod bearings are made of calibrated steel strip filled with an antifriction lead-antimony-tin alloy. The liners are unified with the connecting rod liners of the engine of the Moskvich-408 car. The liners are secured against rotation and axial movements in the lower head of the connecting rod using tendrils stamped at the joint, which fit into grooves milled in the body of the head and connecting rod cover. The liners are installed in the connecting rod head with some interference, and the optimal radial (oil) clearance between the liner and the shaft journal must be ensured. To meet these requirements, the hole in the lower head of the connecting rod is bored to a high accuracy class in assembly with the cover. Therefore, the connecting rod caps cannot be swapped from one connecting rod to another, since they are not interchangeable. The assembled connecting rods are divided at the factory into five weight groups with a difference of 5 g and are marked with paint. Connecting rods of the same weight group are installed on each engine. Flywheel 9 (Fig. 16), made in the form of a disk with a hub and a massive rim, is installed on the conical shank of the crankshaft on a segment key and secured with a special bolt 14, screwed into the hole in the crankshaft journal. The bolt is secured against loosening with a lock washer. The flywheel is statically balanced at the factory. The relative position of the crankshaft and the flywheel is fixed with a key when installing the flywheel on the shaft, which is necessary to maintain the position of the timing marks on the flywheel rim, intended for setting the ignition timing. The clutch is installed in the internal cavity of the flywheel. To prevent oil leakage from the engine crankcase, an oil seal 10 and an oil deflector washer 11 are installed in the bore of the rear wall of the crankcase. The working edge of the rubber seal seal covers the ground belt of the flywheel hub. The piston (Fig. 18) is cast from aluminum alloy. The piston crown is convex with recesses to accommodate the valve heads. To ensure heat removal, the piston bottom is made massive with a smooth transition into the cylindrical part of the piston head. The piston head has three grooves: the top two are for compression rings, the bottom is for the oil scraper ring. A narrow annular slot is machined above the groove for the upper compression ring, the purpose of which is to remove part of the heat flow and thereby protect the upper ring from burning and sticking. Along the forming groove of the oil scraper ring and the piston head, holes are drilled at regular intervals to drain the oil collected by the oil scraper ring from the cylinder walls. The piston pin bosses are reinforced with ribs that connect them to the piston head and crown. The hole for the piston pin and piston boss is offset by 1.5 mm from the diametrical the plane of the piston towards the more loaded lateral surface. To ensure correct installation of the piston in the cylinder, there is an arrow on its bottom, which on both pistons should point forward, i.e., towards the centrifuge. The displacement of the finger contributes to a smoother, almost shock-free, movement of the piston when changing the direction of movement. Based on the size of the piston pin hole, pistons are sorted into four groups and marked with paint on the boss. Below the hole for the piston pin on the skirt there is a groove for the second oil scraper ring. The bottom of the groove has slots located at equal distances around the circumference, designed to discharge excess oil. The geometry of the side surface of the piston is selected in such a way that the piston is installed in the cylinder with the smallest possible clearance, which ensures the piston operates without knocking on a cold engine and guarantees reliable operation, without jamming and scuffing, on a warm engine. To equalize the deformation of the piston during operation, the side surface of its skirt has a special configuration - conical in longitudinal and elliptical in cross sections. Based on the size of the largest diameter of the lower part of the piston skirt, they are sorted into four groups corresponding to the size groups of the cylinders. The diameter of the skirt slopes towards the bottom of the piston. Piston pin 2 (Fig. 18) is made of alloy steel grade 12ХНЗА. By the nature of the connection with the piston and connecting rod, the pin is of the floating type, i.e., it has the ability to rotate freely in the joints when the engine is warm, which ensures more uniform wear of the pin along its diameter and length. The pin is protected from lateral displacement by installing spring retaining rings 3 of circular cross-section in the grooves of the piston bosses. By diameter, the pins are sorted into four groups, corresponding to the size groups of the holes for the pin in the piston boss and in the upper head of the connecting rod. Piston rings are made of cast iron of a special composition with appropriate heat treatment. Two compression rings 5 and 6 (Fig. 18) of rectangular cross-section are installed on the piston, ensuring the tightness of the working volume of the cylinder. Reducing oil consumption to 100-150 g per 100 km while ensuring completely satisfactory lubrication of the working surface of the pistons and cylinders of the MT-801 engine was achieved as a result of installing two oil scraper rings 4, located on the piston above and below the piston pin. Unlike the solid surface of compression rings, the surface of oil rings has slots milled around the circumference of the ring at regular intervals. Thanks to these cracks, the bearing surface of the oil scraper ring decreases and the specific pressure on the cylinder wall increases. Therefore, excess oil is removed from the cylinder walls when the ring moves and is discharged into the crankcase through slots in the ring and drillings in the piston groove. Engine piston rings have a direct lock (joint). To limit gas breakthrough, the piston rings are installed during installation so that the joints are located at an angle of 120°. The thermal gap at the joints of the rings installed in the cylinder should be 0.25 -0.45 mm. The rings are installed in the piston grooves with an end clearance of 0.04-0.08 mm. Compression rings are in direct contact with hot gases and operate under harsh conditions, especially the upper ring 6. Therefore, the upper compression ring is covered with a layer of crown with a thickness of 0.13-0.18 mm. Cylinder (Fig. 15). The MT-801 engine, like most air-cooled engines, has 13 separate interchangeable cylinders with liners cast from cast iron of a special composition of high hardness. The rigidity of the liner and its preservation of the correct geometric shape during engine operation with the cylinder mounting pins tightened are ensured by the sufficient thickness of the liner walls (4 mm) and two support belts in the upper and lower parts. The upper belt of the liner protrudes beyond the end plane of the cylinder and is designed for mating with the cylinder head. The lower belt of the liner rests on the engine crankcase flange. The cylinder liner is connected to the aluminum alloy of the cylinder body through a special process, that is, it is hot cast using a special technology that ensures a chemical and diffuse connection of aluminum and iron in a thin boundary layer along the surface of the liner. The bimetallic cylinder of the MT-801 engine has an advantage over the solid cast iron cylinder of the K-750 engine; With approximately the same wear resistance of the cylinder working surface in both engines, the cooling efficiency of the MT-801 cylinder is significantly higher, since the aluminum alloy has high thermal conductivity. Good heat removal from the cylinder walls is facilitated by symmetrically located cooling fins. The height of the ribs smoothly changes along the cylinder from 30 mm at the top rib to 17 mm at the bottom. The horizontally opposed arrangement of the cylinders on the engine contributes to their good cooling. However, due to the presence of a side trailer stroller, the cooling conditions of the right cylinder are somewhat worsened. Therefore, the temperature of the right cylinder on a well-warm-up engine is usually slightly higher than the temperature of the left one. The inner surface of the liner is subjected to diamond boring and subsequent finishing, as a result of which the diameter size and the correct geometric shape are maintained with high accuracy. Based on their diameter, the cylinders are sorted into four groups corresponding to the piston size groups. The size group index is stamped at the end of the cylinder flange. The cylinder is secured to the engine crankcase together with the cylinder head with four long anchor pins. For the passage of the studs, four holes are drilled in the cylinder flange, passing through all the ribs of the cylinder. The fifth hole is for the drainage tube. The cylinder is centered in the bore of the crankcase flange by the lower protruding flange of the liner and rests on a massive flange. A sealing gasket made of paper is placed at the joint between the cylinder flange and the crankcase. The cylinder head is an aluminum alloy casting. The right and left heads are not interchangeable. The head is the hottest part of the engine cylinder. Therefore, to ensure intensive heat removal, it has a developed silvered surface. A hemispherical combustion chamber is located in the center of the head. On its surface there are holes with bronze seats pressed into them for the heads of the intake and exhaust valves. On the jumper between them there is a bronze fitting cast into the body of the head with a threaded hole for the spark plug. Channels are cast in the body of the head for the intake of fresh working mixture and the exhaust of exhaust gases. On the outer surface of the head there are bosses for placing valves and four stands for rocker arms, cast integrally with the head. The valve drive parts are located under the head cover 21 (Fig. 16), which is attached to the head using a pin and a shaped nut. A rubber sealing gasket is installed between the head cover and the machined upper end of the cylinder head. The cylinder head is mounted on the centering collar of the cylinder liner. At the junction between the head and the end of the sleeve there is a thin sealing gasket made of red copper. |
