PISTONS AND VALVE SPRINGS FOR OPPOSITES
· Engine
With enviable frequency, Opposite questions arise: which pistons to choose, is it possible to put Ural ones on the Dnieper or Dnieper ones on the Urals, how to distinguish pistons for 80th gasoline from pistons for 92, etc. etc. There are also questions about valve springs - is it possible to install non-standard ones, if so, which ones and how? What can be put in place of weak clutch springs?
This article will help to understand the existing diversity.
So, PISTONS.
Pistons are manufactured using different technologies (photo 1). Usually this is casting (for lower valves, as well as standard Ural and Dnieper ones). There is another technology called isothermal stamping (colloquially they usually say "forging", although this is not entirely correct). Both technologies have their pros and cons; in addition, the sizes differ, so we will consider all the options in order.
We look at table 1 and at figure-scheme 1.
PISTONS FOR M-72 and K-750 of interest primarily to lovers of antiquity. They are not suitable for use in more modern motors in view of the large distance from the axis of the finger to the bottom and the large mass. The pistons are interchangeable, they are distinguished by the presence of a groove for the second oil scraper ring in pistons for K-750 (photo 2 and 3).
STANDARD PISTON FOR 650 IMZ ENGINE(photos 4 and 5).
Cast piston with flat bottom, with two oil scraper rings. Provides a low compression ratio requiring the use of gasoline with an octane rating of 76-80.
PROS: affordable price, widespread (in case of a breakdown, you can find a spare piston or rings in any village), the use of inexpensive fuel. There are repair sizes.
CONS: higher coefficient of thermal expansion compared to forged pistons, and, accordingly, a greater tendency to jam when overheated. Poorly resists burnout. Large weight compared to forged pistons. Wide piston rings create increased liner friction, increasing mechanical losses. Partially, losses can be reduced by removing the lower oil scraper ring, which at the same time reduces the mass of the piston. However, an increase in oil consumption is possible.
STANDARD PISTON FOR IMZ 750 ENGINE(photos 6 and 7).
Forged piston with spherical bottom, short skirt and one oil scraper ring. It is allowed to be installed on both 750 and 650 cc engines. Provides an increased compression ratio, which requires the use of AI-92 gasoline. The pin is offset relative to the piston axis, which makes the engine run smoother and reduces wear on the CPG.
PROS: lighter than a standard cast. Less prone to burnout. A lower coefficient of thermal expansion reduces the likelihood of a thermal wedge. Thin piston rings reduce mechanical losses in the ring-cylinder mirror pair.
CONS: high price. Low prevalence in spare parts. Use of Hastings rings of rare dimension. A reduced skirt can THEORETICALLY cause increased piston or cylinder wear. There are known cases of burnout of the pistons in the center with a strong over-depletion of the mixture. There are no repairs.
PISTON MANUFACTURED BY AUTOTECHNOLOGIA, STANDARD DIAMETER 78 MM(photos 8 and 9).
Forged piston with spherical bottom, standard long skirt, one oil scraper ring. The dimension of the rings is the same as on the forged Irbit piston. It is installed on 650- and 750-cc engines. Provides an increased compression ratio for 92 gasoline. The finger is offset relative to the piston axis.
PROS: with a full skirt, it has a mass as small as that of the Irbit forged pistons. Exceptionally high quality material (from a finger strike it rings like crystal) and processing. Optimum skirt shape (barrel-shaped), providing improved skirt lubrication conditions. The price is at the level of Irbit forged pistons.
CONS: it is almost impossible to buy them somewhere other than Moscow. It is believed that the harder material of these pistons can cause accelerated cylinder wear. There are no repair sizes.
PISTON MANUFACTURED BY AUTOTECHNOLOGIA, INCREASED DIAMETER 79 MM
Piston manufactured by Avtotekhnologiya, enlarged diameter 79 mm (photos 10 and 11).
Structurally repeats the piston under the size of 78 mm. Differs in the use of standard piston rings from the VAZ engine.
PROS: Same as size 78 pistons. Use of easily accessible rings makes these pistons ideal for long trips. Some increase in working volume (up to 666 cubic meters). A good option to restore a badly worn motor.
CONS: Same as size 78 pistons. Some increase in weight can reduce the maximum engine speed.
PISTONS FOR MOTORCYCLES OF THE Kyiv PLANT I did not have a chance to examine personally, so the information is given from a third-party source: motodrive.com.ua
The difference between them is in the design of the bottom, mass. All are equipped with standard opposed rings - 2 compression and 2 oil scraper rings per piston.
The disadvantages and advantages are the same as for cast pistons for 650 cc IMZ engines.
PISTONS PRODUCED BY AUTOTECHNOLOGIA FOR DNEPR MOTORCYCLES(photos 12 and 13).
They come in a diameter of 78 mm - for Hastings rings, and 79 mm - for VAZ rings.
Forged pistons, structurally repeat the piston for the MT-10-32 engine with a trapezoidal displacer, but with one oil scraper ring.
ADVANTAGES are the same as for Avtotekhnologii products for IMZ motors: low weight (much less than the lightest cast ones), low thermal expansion coefficient and tendency to jamming, exceptionally high quality.
MINUSES similarly - low prevalence, fears of accelerated wear of cylinders.
Separately, I want to say about pistons with a diameter of 82 mm. The need for such details is experienced by owners of 720 cc Voyages, as well as tuning enthusiasts who want to bore their 650 cc engine to 720, or 750 cc engine to 825.
Factory pistons for a 720 engine cannot be found on sale - “no, son, this is fantastic!”.
The way out is to remake automobiles.
For example, a standard cast piston FROM THE VAZ-2112 ENGINE(photos 14 and 15).
Remaking it is simple: make additional recesses for the valves in the bottom, bore the holes and press in the bushings for the opposite pin with a diameter of 21 mm.
PLUSES: high prevalence of workpiece parts, ease of rework. Use of common inexpensive rings. There are repair sizes.
CONS: VERY large mass - almost 100 grams heavier than a forged piston with a diameter of 78 mm. Such a mass can negate all other forcing work: the maximum engine speed will drop, the load on the crank and connecting rods will increase sharply. A cast piston will have a tendency to seize when overheated. Insufficient height of the sphere will reduce the compression ratio, which will have to be compensated by trimming the cylinder.
In short, this option is only suitable for resuscitation of a 720 cc engine.
It is not categorically suitable for forcing, as blanks you need to look for lightweight, probably forged, pistons.
Engine repair during normal motorcycle operation, as a rule, becomes necessary after several tens of thousands of kilometers, when power drops noticeably due to a decrease in compression in the cylinders, oil consumption increases and smoke from mufflers, knocks and noises appear. With sufficient experience, you can judge the condition of the engine by the noise of its operation or by outward signs. If any violations suddenly appeared, it is advisable to establish the cause of the malfunction before disassembling the engine so as not to touch unnecessary components, because this violates the running-in of rubbing pairs and seals.
When disassembling the engine, as well as other mechanisms (partial or complete), it is recommended to mark the parts so that, after checking, fit and slightly worn ones can be installed in their places.
AT motorcycle engine wear parts include piston rings. They are made from special cast iron. The oil scraper rings of the engines of all motorcycles "Dnepr" and "Ural" are interchangeable, the height of the ring is 5-0.015 mm. Compression rings are not interchangeable: ring 7201217-01 (K750M) has a height of 3 mm, and 6101217 (MT) - 2.5 mm. The designations and dimensions of the piston rings are given in Table. one.
Signs of severe wear of the rings - smoke from mufflers, increased consumption oil (more than 300 cc per 100 kilometers), a decrease in compression, a malfunction of the ventilation system (an increased release of oil through the breather tube is possible). In this case, it is necessary to remove the heads and cylinders, and then check the condition of the parts of the piston group.
When the rings are worn, the gap in their locks increases. The maximum allowable is 3 mm. To measure it, the rings are removed from the piston, marking their location. Then the ring is inserted into the cylinder, its position is aligned with the piston and the gap in the lock is measured with a feeler gauge.
The worn ones are replaced for the first time with rings of normal size, and then, when the cylinder is worn out and bored out, rings and a piston of a repair size are installed. Before installation, a new ring is inserted into the cylinder and the gap in the lock is checked, which should be in the range from 0.20 to 0.6 mm.
Before installing the cylinder in place, lubricate its mirror and piston skirt with engine oil, spread the rings so that their joints are located at an angle of 120 ° - one to the other. When putting the cylinder on the piston, the rings are compressed with a clamp, which can be easily made from tin.
A sign of piston wear is a dull metallic knock in the cylinder area, especially noticeable after starting a cold engine.
The right and left pistons in both engines are the same, cast from heat-resistant aluminum alloy KS-245. The skirt has an oval cross-section, and a conical shape along the longitudinal one. In the MT engine, the axis of the hole for the piston pin is offset from the plane of symmetry by 1.5 mm.
For the correct installation of the piston in the cylinder, an arrow is stuffed on its bottom, which, during installation, must face forward, that is, towards the centrifuge. In this case, when looking at the MT engine from behind, the finger in the piston of the right cylinder is shifted down, and in the piston of the left - up.
The holes for the piston pin are divided into four groups by diameter (through 0.0025 mm) and are marked with paint on the boss (Table 2). According to the outer diameter (measured under the oil scraper ring), the pistons are sorted through 0.01 mm into four groups. The size of the piston group is stuffed on the outer side of the bottom with numbers: 77.95, 77.96, 77.97, 77.98 for the MT engine and 77.93, 77.94, 77.95, 77.96 for the K750M. In addition, the pistons are divided into groups by weight, which matches the color index of the finger hole.
The piston must be replaced if the gap between the cylinder bore and the largest diameter of the skirt (in a plane perpendicular to the pin axis, below the oil scraper ring groove) exceeds 0.25 mm. The clearance can be measured with a feeler gauge when the piston is at the bottom of the cylinder.
If the piston is normal, and only the grooves of the upper, compression rings are worn out (end clearance is more than 0.15 mm) - you can install a ring from the K750M engine on the MT engine, after grinding it in height, taking into account the end clearance within 0.04-0 .07 mm for the top ring and 0.025-0.055 mm for the bottom.
Usually, when the pistons are first replaced, when the cylinders are still worn out a little, to reduce the gap between the mirror and the skirt, you can install a “normal” piston, but with a larger skirt diameter, for example, if the cylinder diameter of the MT engine of group “1” (78.01-78, 00 mm) during operation increased to 78.04-78.03 (which corresponds to group "4"), then the piston "77.95" standing in it should be replaced with a piston with the designation "77.98". In this case, the required clearance of 0.05-0.07 mm will be restored. In the K750 engine, pistons are selected taking into account the provision of a gap of 0.07-0.09 mm.
Pistons are selected not only by the diameter of the skirt, but also by weight in order to maintain the balance of the engine. The difference in weight of the pistons must not exceed 4 g.
The piston pin is made of steel 12HNZA, cemented and heat-treated to a hardness of HRC 56-63. It rotates freely in the upper head of the connecting rod with a clearance of 0.0045-0.0095, but is pressed into the piston bosses with an interference of 0.0045-0.0095 mm. According to the outer diameter, the fingers are divided into four groups through 0.0025 mm and marked with paint on the inner surface (see Table 2).
Clearances of more than 0.01 mm in the connection of the pin with the piston and more than 0.03 mm in the connection of the pin with the connecting rod can cause distinct sharp knocks and intensive wear of parts when changing the engine operating mode. To eliminate these phenomena, it is necessary to replace the piston pin, observing the required marking and its fit in the piston and connecting rod according to Table. 2. When installing the finger, the piston is heated to 80-100 ° C in an oven or in boiling water. Before assembly, the finger is lightly lubricated with engine oil, then the holes in the piston and the upper head of the connecting rod are aligned and the finger is hammered into them with light hammer blows through the mandrel. A lubricated piston pin in the top end of the connecting rod is considered normal when it slides easily into the hole, but does not fall out when placed vertically.
You can remove the finger without heating the piston, but you must use a special tool. If it is not there, you can heat the piston bottom with a blowtorch through a metal sheet and use a mandrel made of soft metal (copper or aluminum) to knock out a finger.
The cylinders of the MT engine are the same, interchangeable. The sleeve is cast from special cast iron and connected in one piece with an aluminum alloy jacket. Sleeve hardness HB 207-255. K750M cylinders are cast from special cast iron, their hardness is HB 207-255. The left and right are not interchangeable, since they differ in the position of the intake and exhaust valves.
Cylinders are divided into four groups according to the inner diameter at intervals of 0.01 mm. The size of the group at MT is stuffed in the lower part of the cylinder shirt (near the flange) from the side of the casings of the rods with the numbers "1", "2", "3" and "4", which correspond to diameters 78.01-78.00; 78.02-78.01; 78.03-78.02 and 78.04-78.03 mm. For K750M, the group index is stuffed on the plane of the valve box.
The cylinder must be replaced or bored to the nearest repair size of the piston if the wear of the upper part of the mirror is 0.15-0.20 mm. When the cylinder becomes conical (wider at the top) and oval, it is no longer possible to restore normal compression by installing new pistons and rings.
Cylinder wear is determined by measuring its diameter with an indicator-bore gauge in three belts located at distances of 15, 50 and 90 mm from the upper end of the cylinder in the connecting rod swing plane and in a plane perpendicular to it.
The worn cylinder is bored and honed to fit the repair diameter of the pistons (increased by 0.2 or 0.5 mm). After processing, the ovality and taper of the mirror must be no more than 0.015 mm, the finish of processing is not lower than the 9th class, the beating of the landing end relative to the mirror is not more than 0.05 mm, the misalignment of the mirror and the outer surface of the cylinder mating with the engine crankcase is not more than 0, 08 mm. The piston is selected so that the mounting gap between the largest diameter of its skirt and the cylinder for the MT is 0.05-0.07 mm, for the K750M it is 0.07-0.09 mm. When installing a new piston in the cylinder, it is necessary to be guided by the information given in Table. 3.
The connecting rod and its cover for the MT engine are stamped from 40X steel, hardness is HB 217-266. The bottom covers of the connecting rods are not interchangeable, so each must be put in its place during assembly. When connecting rods are installed on the crankshaft, the protrusions in their middle part should be directed outward relative to the middle web of the shaft. Inserts are installed in the lower head, which are interchangeable with the connecting rod bearings of the Moskvich-408 engine. A bronze bushing is pressed into the upper head, made of BrOTsS-4-4-2.5-PT-1.5 tape, the hole of which is made with great accuracy. According to its diameter, the connecting rods are divided into four groups (through 0.0025 mm) and marked at the head with a color index (see Table 2).
The assembled connecting rods are divided by weight into seven groups (after 5 g) and marked with paint. Connecting rods with a single-color marking are installed on the crankshaft. nuts connecting rod bolts tighten with a moment of 3.2-3.6 kgf.m. The pin must fit tightly into the bolt hole. Used pins must not be used.
Possible defects of the connecting rod - wear of the bushing under the piston pin, bending and twisting of the connecting rod body.
The bushing diameter can be measured with an indicator caliper. If the clearance between bushing and piston pin is more than 0.03 mm, the bushing must be replaced. To do this, it is necessary to make a new bushing from tin bronze BrOF10-1 or BrOTsS-4-4-2.5 and press it in with an interference fit of 0.027-0.095 mm. Drill a hole with a diameter of 2.5 mm in the bushing for lubricating the piston pin and turn it with a reamer to a diameter of 21 + 0.007 mm. Remove a 1x45º chamfer from the ends of the bushing. It remains to measure the actual size of the hole, mark it in accordance with the table. 2 and select a piston pin with the corresponding color marking.
The bending of the connecting rod is characterized by the relative displacement of the axes of the holes of the upper and lower heads in the vertical (bending) or horizontal (twisting) planes. Axes displacement is allowed no more than 0.04 mm over a length of 100 mm. The center distance between the axes of the new connecting rods is 140 ± 0.1 mm.
Connecting rod bolts must not have dents, traces of drawing and thread stripping, cracks and other defects. The diameter of the lower head of the connecting rod is measured with the inserts inserted and the cover bolts tightened with a force of 3.2-3.5 kgf.m.
If the clearances in the connecting rod bearings are not more than 0.10 mm, and the ovality and taper of the journals crankshaft does not exceed 0.05 mm, you can not grind the necks, but install liners of a normal or reduced size by 0.05 mm (first repair).
The crankshaft of the MT engine is cast from high-strength cast iron VCh50-2 and heat-treated to a hardness of HB 212-255. The nominal diameter of its main journals is 45 ± 0.08 mm, the connecting rod journals are 48-0.025 mm.
The suitability of the crankshaft for further operation is determined by the degree of wear of the connecting rod journals. Their diameter is measured with a micrometer in two mutually perpendicular planes in two places at a distance of 2.5 mm from the fillets. The distance between the cheeks of the connecting rod journals is 28.5 + 0.14 mm, the radius of the fillets is 1.5-2.0 mm, the finish is not lower than the 9th grade.
In a new engine, the gap between the neck and the liners is 0.025-0.085 mm. A sign of wear on the connecting rod journals is the appearance of thuds in the lower part of the crankcase and a decrease in pressure in the lubrication system.
With significant wear, the necks are ground to the nearest repair size (Table 4) and the corresponding liners are placed. After processing the necks, all channels, including traps, must be cleaned of chips and washed several times under pressure and blown with compressed air. As a result of grinding, the connecting rod journals must meet the following conditions: ovality and taper not more than 0.015 mm; non-parallelism of the axes of the connecting rod journals to the axes of the main journals - no more than 0.02 mm along the length of the neck.
After checking, the crankshaft is assembled, paying special attention to the correct installation of the connecting rods, and installed in the engine crankcase, as shown in the figure. When properly assembled, the shaft should rotate easily in the main bearings.
The engine pistons of Dnepr and Ural motorcycles are cast from heat-resistant aluminum alloy and heat-treated. The piston consists of a head with a spherical or flat bottom, a skirt and bosses. Piston rings are installed on the piston (two compression and two oil scraper). In the grooves under the piston rings there are through holes for oil drainage. The piston skirt is made in a special oval shape. The larger diameter of the skirt is located in a plane perpendicular to the axis of the piston pin. The piston skirt also has a conical shape. The difference between the larger and smaller diameter of the skirt is 0.015 mm. The diameter of the upper part of the skirt is less than the diameter of the lower part by 0.03 - 0.05 mm. The ovality and taper of the skirt are necessary so that, with a small gap between it and the cylinder, the piston, expanding from heating, does not stick in the cylinder. The pistons are the same for both cylinders. Depending on the diameter, the cylinders are divided into groups (Table 2.1).
To reduce the noise of the piston during its operation, the axis of the hole for the piston pin in the MT 10-32 engine is offset by 1.5 mm relative to the axis of symmetry. To correctly install such a piston in the cylinder, an arrow is stamped on the bottom of its bottom. During installation, the arrow on the pistons of both cylinders must point forward towards the centrifuge. In this case, when looking at the engine from behind, the pin in the piston of the right cylinder should be shifted down, and in the piston of the left cylinder - up.
The pin holes in the pistons of the K-750M and M67-36 engines are made without displacement of the pin axis from the diametral plane of the piston. The pistons of the K-750M and M67-36 engines have a flat bottom, and the MT 10-32 piston has a flat bottom with an ejector.
The finger holes are divided into groups at intervals of 0.0025 mm and marked with paint on the sidewall (Table 2.2). The allowable wear of the piston pin hole must not exceed 0.02 mm. These bores contain grooves for circlips that assist in axial displacement of the piston pin. Pistons to cylinders are selected with the necessary clearance. To facilitate selection, pistons and cylinders are sorted through 0.010 mm. Their dimensions are stamped on inside piston bottom.
In addition, the pistons are grouped by weight, which matches the colored index of the piston pin hole. The difference in the mass of the engine pistons should not exceed 0.004 kg. The piston assembly with rings and pin is weighed. For selected pistons, the color marking of the holes for the piston pin must match the marking of the hole in the upper head of the connecting rod. The marking paint on the pistons is applied to the bottom
the surface of one of the bosses, on the connecting rods - at the top head.
|
Table 2.2 Ma |
fattening of size groups of pins, pistons and connecting rods |
||
|
Color markings |
Finger diameter, mm |
Bore diameter in piston bosses, mm |
Diameter of the hole in the upper head of the connecting rod, mm |
|
White |
21,0000- 20,9975 |
20,9930-20,9905 |
21,0070-21,0045 |
|
Black |
21,9975- 20,9950 |
20,9905-20,9880 |
21,0045-21,0020 |
|
Red |
20,9950- 20,9925 |
20,9980-20,9855 |
21,0020-20,9995 |
|
Green |
20,9925- 20,9900 |
20,9855-20,9830 |
20,9995-20,9970 |
Table 2.3 Repair dimensions of cylinders and pistons
|
Brand move |
Cylinder and piston size |
Diameter cylinder, |
Piston designation according to the catalog |
Piston diameter, mm |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
MT10- |
78,20-78,24 |
KM3-8.15501237-P1 |
78,18-78,14 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
mtu- |
78,50-78,54 |
KM3-8.15501237-P2 |
78,48-78,44 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
750M |
1st repair (increased by 0.2 mm) |
78,20-78,24 |
72Н01237-Р1 |
78,15-78,11 |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
750M |
2nd repair (increased by 0.5 mm) |
78,50-78,54 |
72Н01237-Р2 |
78,45-78,41 |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
M67-36 |
1 repair (increased by 0.2 mm) |
Engine repair during normal motorcycle operation, as a rule, becomes necessary after several tens of thousands of kilometers, when power drops noticeably due to a decrease in compression in the cylinders, oil consumption increases and mufflers smoke more strongly, knocks and noises appear. With sufficient experience, you can judge the condition of the engine by the noise of its operation or by external signs. If any violations appeared suddenly, it is advisable to establish the cause of the malfunction before disassembling the engine so as not to touch unnecessary components. because in this case, the connections of the run-in pairs and seals are broken. (Behind the wheel, No. 2, 1984) When disassembling the engine, as well as other mechanisms (partial or complete), it is recommended to mark the parts so that, after checking, fit and slightly worn ones can be installed in their places. In a motorcycle engine, piston rings are among the wear parts. They are made from special cast iron. The oil scraper rings of the engines of all motorcycles "Dnepr" and "Ural" are interchangeable, the height of the ring is 5-0.015 mm. Compression rings are not interchangeable: ring 7201217-01 (K750M) has a height of 3, and 6101217 (MT) - 2.5 mm. The designations and dimensions of the piston rings are given in Table 1.
Signs of ring failure are smoke from mufflers, increased oil consumption (more than 300 cm3 per 100 kilometers), reduced compression, malfunction of the ventilation system (increased oil emission through the breather tube is possible). In this case, it is necessary to remove the cylinder heads, and then check the condition of the parts of the piston group. When the rings are worn, the gap in their locks increases. The maximum allowable is 3 mm. To measure it, the rings are removed from the piston, marking their location. Then the ring is inserted into the cylinder, its position is aligned with the piston and the gap in the lock is measured with a feeler gauge. Before installing the cylinder in place, lubricate its mirror and piston skirt with engine oil, spread the rings so that their joints are located at an angle of 120 ° to one another. When putting the cylinder on the piston, the rings are compressed with a clamp, which can be easily made from tin. A sign of piston wear is a dull metallic knock in the cylinder area, especially noticeable after starting a cold engine. The right and left pistons in both engines are the same, cast from heat-resistant aluminum alloy KS-245. The cross section of the skirt is oval. and along the longitudinal - conical shape. In the MT engine, the axis of the hole for the piston pin is shifted from the plane of symmetry by 1.5 mm. For the correct installation of the piston in the cylinder, an arrow is stuffed on its bottom, which, during installation, must face forward, that is, towards the centrifuge. In this case, when looking at the MT engine from behind, the finger in the piston of the right cylinder is shifted down, and in the piston of the left - up.
According to the outer diameter (measured under the oil scraper ring), the pistons are sorted through 0.01 mm into four groups. The size of the piston group is stuffed on the outer side of the bottom with numbers: "77.95". "77.96". "77.97", "77.98" for the MT engine and "77.93". "77.94", "77.95". "77.96" for K750M. In addition, the pistons are divided into groups by weight, which matches the color index of the piston pin hole. The piston must be replaced if the gap between the cylinder bore and the largest diameter of the skirt (in a plane perpendicular to the axis of the pin, below the groove for the oil scraper ring) exceeds 0.25 mm. The clearance can be measured with a feeler gauge when the piston is at the bottom of the cylinder. If the piston is normal, and only the grooves of the upper, compression rings are worn out (end clearance is more than 0.15 mm), you can install a ring from the K750M engine on the MT engine. after grinding it in height, taking into account the end clearance within 0.04-0.07 mm for the upper ring and 0.025-0.055 mm for the lower one. Usually, when the pistons are first replaced, when the cylinders are still a little worn, to reduce the gap between the mirror and the skirt, you can install a “normal” piston, but with a larger skirt diameter. For example, if the cylinder diameter of the MT engine of group “1” (78.01-78.00 mm) during operation increased to 78.04-78.03 (which corresponds to group “4”), then the piston “77.95” standing in it should be replaced with a piston with designation "77.98". In this case, the required clearance of 0.05-0.07 mm will be restored. In the K750 engine, pistons are selected taking into account the provision of a gap of 0.07-0.09 mm. Pistons are selected not only by the diameter of the skirt, but also by weight in order to maintain the balance of the engine. The difference in weight of the pistons must not exceed 4 g. Clearances of more than 0.01 mm in the connection of the pin with the piston and more than 0.03 mm in the connection of the pin with the connecting rod can cause distinct sharp knocks and intensive wear of parts when changing the engine operating mode. To eliminate these phenomena, it is necessary to replace the piston pin, observing the required marking and its fit in the piston and connecting rod according to Table. 2. When installing the finger, the piston is heated to 80-100 ° C in the oven or in boiling water; Before assembly, the finger is lightly lubricated with engine oil, then the holes in the piston and the upper head of the connecting rod are aligned and the finger is hammered into them with light hammer blows through the mandrel. A lubricated piston pin fits into the top end of the connecting rod when it slides easily into the hole, but does not fall out when its axis is vertical. You can remove the finger without heating the piston, but you must use a special tool. If it is not available, you can heat the piston bottom with a blowtorch through a metal sheet and, using a mandrel made of soft metal (copper or aluminum), knock out the pin, as shown in fig. one. The cylinders of the MT engine are the same, interchangeable. The sleeve is cast from special cast iron and connected in one piece with an aluminum alloy jacket. Sleeve hardness HB 207-255. K750M cylinders are cast from special cast iron, their hardness is HB 207-255. The left and right are not interchangeable, since they differ in the position of the inlet and outlet valves. Cylinders are divided into four groups according to the inner diameter at intervals of 0.01 mm. The size of the group at MT is stuffed in the lower part of the cylinder shirt (near the flange) from the side of the casings of the rods with the numbers "1", "2", "Z" and "4", which correspond to diameters 78.01-78.00; 78.02 - 78.01; 78.03 - 78.02 and 78.04 - 78.03 mm. For K750M, the group index is stuffed on the plane of the valve box. The cylinder must be replaced or bored to the nearest repair size of the piston if the wear of the upper part of the mirror is 0.15-0.20 mm. When the cylinder becomes tapered (wider at the top) and oval, it is no longer possible to restore normal compression by installing new pistons and rings. Cylinder wear is determined by measuring its diameter with an indicator-bore gauge in three belts located at distances of 15, 50 and 90 mm from the upper end of the cylinder in the connecting rod swing plane and in a plane perpendicular to it. The worn cylinder is bored and honed to fit the repair diameter of the pistons (increased by 0.2 or 0.5 mm). After processing, the ovality and taper of the mirror should be no more than 0.015 mm, the finish of processing should not be lower than class 9, the beating of the landing end relative to the mirror should be no more than 0.05 mm, the misalignment of the mirror and the outer surface of the cylinder mating with the engine crankcase should be no more than 0.08 mm . The piston is selected so that the mounting gap between the largest diameter of its skirt and the cylinder for the MT is 0.05-0.07 mm, for the K750M it is 0.07-0.09 mm. When installing a new piston in the cylinder, it is necessary to be guided by the information given in Table. 3. The connecting rod and its cover for the MT engine are stamped from 40X steel, hardness is HB 217-266. The bottom covers of the connecting rods are not interchangeable, so each must be put in its place during assembly. When connecting rods are installed on the crankshaft, the protrusions in their middle part should be directed outward relative to the middle web of the shaft. In the lower head there are liners that are interchangeable with the connecting rod liners of the Moskvich-408 engine. A bronze bushing made of BrOTsS-4-4-2.5-PT-1.5 tape is pressed into the upper head. the hole is made with great precision. According to its diameter, the connecting rods are divided into four groups (through 0.0025 mm) and marked at the head with a color index (see Table 2). The assembled connecting rods are divided by weight into seven groups (after 5 g) and marked with paint. Connecting rods with one-color markings are installed on the crankshaft. The nuts of the connecting rod bolts are tightened with a torque of 3.2-3.6 kgf / m. The pin must fit tightly into the bolt hole. Used pins must not be used. The bushing diameter can be measured with an indicator caliper. If the clearance between bushing and piston pin is more than 0.03 mm, the bushing must be replaced. To do this, it is necessary to make a new bushing from BrOFYu-1 or BrOTsS-4-4-2.5 tin bronze and press it in with an interference fit of 0.027-0.095 mm. Drill a hole with a diameter of 2.5 mm in the bushing to lubricate the piston pin and turn it with a reamer to a diameter of 21 mm. Remove the chamfer 1x45 ° from the highlanders of the bushing. It remains to measure the actual size of the hole. mark it in accordance with the table. 2 and select a piston pin with the corresponding color marking. Connecting rod bolts must not have dents, traces of drawing and thread stripping, cracks and other defects. The diameter of the lower head of the connecting rod is measured with the inserts inserted and the cover bolts tightened with a force of 3.2-3.5 kgf. If the clearances in the connecting rod bearings are not more than 0.10 mm, and the ovality and taper of the crankshaft journals do not exceed 0.05 mm, you can not grind the necks. and install liners of normal or reduced size by 0.05 mm (first repair). The suitability of the crankshaft for further operation is determined by the degree of wear of the connecting rod journals. Their diameter is measured with a micrometer in two mutually perpendicular planes in two places at a distance of 2.5 mm from the fillets. The distance between the cheeks of the connecting rod journals is 28.5 + 0.14 mm, the radius of the fillets is 1.5-2.0 mm, the finish is not lower than the 9th grade. In a new engine, the gap between the neck and the liners is 0.025-0.085 mm. A sign of wear on the connecting rod journals is the appearance of thuds in the lower part of the crankcase and a decrease in pressure in the lubrication system. After checking, the crankshaft is assembled, paying special attention to the correct installation of the connecting rods, and installed in the engine crankcase, as shown in fig. 2. When properly assembled, the shaft should rotate easily in the main bearings. More than three years ago, the Kyiv Motorcycle Plant began producing motorcycles of the Dnepr K-650 family with an MT-8 engine. Last year, they gave way to a more advanced model with power unit equipped with a reverse gear. Many owners of these powerful enduring machines, who managed to cover tens of thousands of kilometers, have questions related to engine repair. Readers will find answers to them in the article published here by specialists from the Kyiv Motorcycle Plant. Power units "Dnepr" (MT-8 and MT-9) differ from all previous engines that were used on domestic heavy motorcycles. First of all, they have a one-piece, not a composite, crankshaft with plain bearings (liners) on the crankpins. As a result, the engine has become more durable and its repair has been simplified. In order to most fully imagine the dimensions, fit and allowable wear of the most important parts, let's get acquainted separately with the most important engine components and their parameters. Crankshaft. It is made of ductile iron and is supported by two bearings. The front one - ball 209 - is installed in a special housing bolted to the engine crankcase, the rear - roller 42209 - is pressed into the crankcase socket. The connecting rod journals of the shaft with a diameter of 48 mm are made hollow so that, under the action of centrifugal force, mechanical impurities remaining in the oil after cleaning in a centrifuge are retained in them. Connecting rods - forged steel, I-section. A bronze bushing rolled from a tape is pressed into the upper head, then bored out to a diameter of 21 mm. The lower head of the connecting rod is made detachable to simplify repairs. It should be borne in mind that, since it is not symmetrical, the connecting rod caps are not interchangeable. When assembling, the connecting rods are placed so that the protrusions and their middle part are turned to the sides opposite the middle cheek of the crankshaft. The connecting rods assembled at the factory are divided by weight into five groups (after 5 g) and are marked on the bottom cover with paint: blue, green, red, black and white. Only single-color connecting rods are mounted on the crankshaft. The nuts of the connecting rod bolts are tightened with a force of 3.2-3.6 kgm. The cotter pins locking these nuts must fit tightly into the bolt holes, without any gap. : 1 - generator rotor gear; 2 - generator G-414; 3 - camshaft; 4 - pusher; 5 - rod casing seal; 6 - rod; 7 - plug with oil dipstick; 8 - connecting rod; 9 - cylinder; 10 - piston; 11 - combustion chamber; 12 - spark plug; 13 - cylinder head cover; 14 — cover fastening screw; 15 - rocker; 16 — crackers of fastening of the valve: 17 — a plate of a spring of the valve; 18 - valve guide; 19 - valve springs; 20 - valve; 21 - valve seat; 22 - outlet pipe; 23 - finger: 24 - pallet; 25 - mesh filter; 26 - oil pump; 27 - cranked feces; 28 - oil pump drive gear; 29 - centrifuge; 30 - front crankcase cover; 31 - generator drive gear; 32 - breaker-distributor; 33 - front cover; 34 - centrifuge key; 35 - camshaft drive gear key; 36 flywheel key; 37 - connecting rod head bolt; 38 - compression rings: 39 - oil scraper rings; 40 - sleeve; 41 - lock washer; 42 - liners; 43 - connecting rod head cover.
1 - channel in the casing of the rod for supplying oil to the cylinder head; 2 - groove for oil in the pusher; 3 - channel for draining oil from the rear main bearing; 4 - channel in the cheek of the crankshaft; 5 - holes for lubrication of the connecting rod bearing: 6 - holes for lubrication of the piston pin in the head of the connecting rod and pistons; 7 trap; 8 - channel in the crankshaft; 9 - centrifuge; 10 - hole in the screen; 11 - channel supplying oil to the centrifuge; 12 - hole for draining oil from the centrifuge; 13 - oil pump; 14 - suction channel of the oil pump; 15 - channel for bypassing oil; 16 - mesh filter; 17 - hole for filling oil; 18 - hole for draining oil; 19 - pressure reducing valve: 20 - channel for supplying oil to the pressure reducing valve; 21 - channel for draining oil from the cylinder head: 22 - main oil line; 23 - hole for mounting the pressure sensor; 24 - oil pressure sensor in the main line; 25 - signal light for emergency oil pressure; 26 - centrifuge body: 27 - diaphragm; 28 - gasket; 29 - centrifuge cover; 30 - bolt securing the centrifuge cover: 31 - oil pump drive gear. The lower head uses trimetallic connecting rod bearings(same as for Moskvich 408 engines), which have high antifriction properties, high bearing capacity and durability. The diametral clearance between the connecting rod journal of the shaft and the liners can be in the range of 0.025-0.075 mm. When it is increased to 0.1 mm, a dull knock occurs in the central part of the engine crankcase. In this case, remove the connecting rod and check the condition of the crankshaft journals and liners. If the ovality and taper of the necks exceeds 0.03 mm, they are ground to the nearest repair size (see table 1) and the corresponding liners are installed. We draw attention to the fact that when grinding the connecting rod journals, it is necessary to maintain the fillet radii in the range of 1.5–2.0 mm.
Table. one Repair size inserts differ from the “normal” one by 0.05; 0.25; 0.50; 0.75; 1.00 and 1.25 mm inside diameter. With slight wear of the necks, you can use liners of normal or reduced sizes by 0.05 mm.
The pistons are cast from a special aluminum alloy and heat treated. To reduce the noise that occurs when the piston changes direction at top dead center, the axis of the pin hole is offset by 1.5 mm from its diametral plane. An arrow is marked on the bottom, which should point towards the centrifuge during installation. The piston is equipped with two compression and two oil scraper rings. The compression rings are interchangeable with the M-63 Ural-2 engine rings, and the oil scraper rings are with the M-63 and Piston pin - floating type. It is installed in the piston bosses with an interference of 0.0045 to 0.0095 mm, and in the bushing of the upper connecting rod head with a clearance of 0.0045 to 0.0095 mm. To ensure these landings, the fingers, the holes of the piston bosses and the upper head of the connecting rod, depending on their diameter, are divided into four groups and marked with paint (see table 3). Clearances of more than 0.01 mm in the connection of the pin with the piston and more than 0.03 mm in the connection of the pin with the connecting rod cause knocking when changing the engine operating mode and intensive wear of parts. To eliminate these phenomena, it is necessary to replace the piston pin, observing the required fit in the piston and connecting rod. When installing a finger, the piston is heated to 80-100 ° in an oven or in boiling water. Engine cylinders - bimetallic, interchangeable. Their aluminum alloy jacket is bonded to a cast iron sleeve by diffusion. This made it possible to significantly reduce the heat stress of the piston group and ensure its performance under forced modes. The need to repair the cylinder, replace the piston and its rings is caused by a decrease in compression in the cylinders (due to the wear of these parts), accompanied by a drop in power, an increase in oil consumption and strong smoke from the mufflers. When monitoring the state of the engine, the cylinder diameter is measured with an inside gauge in five belts located at distances of 15, 25, 50, 75 and 85 mm from the upper end of the cylinder in the swing plane of the connecting rod and in a plane perpendicular to it. The gap between the cylinder and the piston as a result of wear should not exceed 0.25 mm. With a larger clearance, the cylinder should be bored to the nearest repair size and the appropriate piston should be installed, guided by table 4. The piston is selected so that the gap between the largest diameter of its skirt and the cylinder is 0.05-0.07 mm (as in a new engine). Table. 3 "Normal" pistons and cylinders are divided into four size groups, differing in diameter by 0.01 mm (pistons according to the largest diameter of the skirt, and cylinders according to the largest diameter of the mirror). The size of the piston group is stamped on the outer side of its bottom with the numbers 77.95; 77.96; 77.97 and 77.98, and the designation of the cylinder group is on the end face of its flange from the side of the casings of the rods with the numbers 1; 2; 3 and 4, which correspond to diameters of 78.01–78.00 mm; 78.02 - 78.01 mm; 78.03-78.02 mm; 78.04 - 78.03 mm. In a slightly worn cylinder, to reduce the gap between its mirror and the piston skirt, you can install a “normal” piston, but with a large skirt diameter. For example, if the diameter of the cylinder of group “1” (78.01–78.00 mm) during operation increased to 78.04–78.03 mm (which corresponds to group “4”), then the piston standing in it “77.95 ” should be replaced with a piston with the designation “77.98”. In this case, the required clearance of 0.05-0.07 mm will be restored. Table. four Pistons are selected not only by the diameter of the skirt, but also by weight (to maintain the balance of the engine). Depending on the actual weight, the parts are divided into four groups, the designation of which coincides with the color index of the holes for the piston pin. The pistons in both cylinders must have the same color marking. The cylinder head is cast from aluminum alloy along with a bronze fu-torque for the candle. The combustion chamber made in the head has a hemispherical shape. Valve seats made of bronze Br. AZhN-10-4-4 L and bronze valve guides Br. OF 6.5-0.15. The heads and cylinders are attached to the engine crankcase by means of four anchor studs. gas distribution mechanism. Valves made of heat-resistant steel type EP-303 are located in the head at an angle of 38° to the vertical axis of the cylinder. On their "tulip" heads with an outer diameter of 37 mm, landing chamfers are made at an angle of 45 °. To increase the durability of the end of the valve stem, a steel cap is put on it, which has high wear resistance. Valve tappets are cast from special cast iron. Their ends, in contact with the camshaft cams, are bleached to a hardness of NKS 50-60. The push rods are made of duralumin, which ensures a minimum change in the gaps between the rocker arm and the valve when the engine is heated. Heat-treated steel tips are pressed onto the ends of the rods. Camshaft steel, forged. Unlike the engines of other heavy motorcycles, the profile of the Dnepr shaft cams is designed according to a new, more advanced method. Thanks to this, the valve rises and falls more smoothly, the gas distribution mechanism works with less noise and makes it possible to increase the shaft speed to 6000 rpm. The duration of the intake and exhaust strokes is the same and amounts to 378 ° of the crankshaft angle. The exhaust valve opens when the piston is 109° short of bottom dead center and closes 89° after it has passed top dead center. The inlet valve opens 69° east. m. t. and closes after 129 ° after n. m. t. The indicated phases are provided with a gap of 0.1 mm between the valve and the rocker arm on a running warm engine. This value corresponds to a gap of 0.07 mm on a cold engine. When checking and adjusting the clearance between the valve stem and the end of the rocker arm, it is necessary to install a piston. for example, the left cylinder in c. m.t. compression stroke. To do this, turn the crankshaft so that the “B” mark on its flywheel is aligned with the mark on the engine crankcase (both valves are closed). The marks are visible in the viewing window on the crankcase, which is closed with a rubber stopper. The MT-8 and MT-9 engine lubrication system is combined. Pressurized oil is supplied only to the connecting rod bearings, the rest of the rubbing pairs are lubricated with oil mist. The oil pump is gear type. Its performance is calculated with a margin for all engine operating modes. Excess oil is passed back to the suction cavity through a plunger-type pressure reducing valve, which is adjusted at the factory and does not require adjustment during operation. The pressure in the lubrication system at medium engine speeds is in the range of 3.5–4.5 kg/cm2. As you know, plain bearings require normal operation cleaner oil than rolling bearings. Therefore, the lubricant supplied to the connecting rod bearings undergoes a two-stage cleaning: first in a centrifuge, and then in the cavities of the connecting rod journals under the action of centrifugal force. This significantly increases the durability of the connecting rod bearings. The operation of the lubrication system is controlled by a signal lamp connected to a membrane-type sensor. It works when the pressure in the line drops to 1.4-1.8 kg / cm2, including at this moment the lamp installed in the headlight of the motorcycle. If the oil pressure is below the permissible level, the motorcycle must not be operated. The lubrication system must be constantly paid attention, especially during the engine break-in period, when the parts are running in: At this time, the oil is most intensively contaminated with metal particles. Therefore, after 500, 1000 and 2500 kilometers, it is necessary to change it (on a hot engine, with crankcase flushing and a pan removed for this purpose). Fresh grease is poured through a fine mesh to prevent dirt and water from entering the engine. Every 10,000-15,000 kilometers it is recommended to clean and rinse the centrifuge. When repairing the engine, when the crankshaft is removed, unscrew the plugs of the oil cavities of the connecting rod journals, clean them inside and rinse thoroughly. Plugs after wrapping must be sealed. The main malfunctions of the lubrication system are low pressure at low and medium shaft speeds or high pressure at all speeds. In both cases, the cause is a clogged pressure reducing valve due to the use of dirty oil. To clean the valve, drain the oil from the crankcase, remove its sump, disconnect the oil receiver and unscrew the oil intake tube. Next, remove the camshaft cover, centrifuge, camshaft gear with shaft, timing drive gear and front bearing housing with oil pump. It should be noted that even a short-term malfunction of the lubrication system can lead to engine failure. As engine oil it is necessary to use autotractor AS-8 (M8B) GOST 10541-63 in summer and winter. Substitutes can serve in the summer - industrial oil 50 (machine SU) GOST 1707-51; in winter - a mixture consisting of 80% machine SU and 20% spindle AC GOST 1642-50. Other oils are not recommended. In order to prevent the ingress of road dust into the engine crankcase through the mounting gaps of the breather, under the action of vacuum, its tube is connected to the air filter by means of a hose made of petrol-resistant rubber. Owners of the Dnieper should take into account that when using a motorcycle in winter, an ice plug can form in the hose (from the moisture contained in crankcase gases), which causes an increase in pressure in the crankcase and squeezing grease through the connectors. To prevent the accumulation of moisture in the tube, it is disconnected from air filter and drop. The ignition system of the MT-8 and MT-9 engines is the same as the K-750M. It consists of a PM-05 breaker-distributor and a B2-B coil. The gap between the contacts of the breaker is set within 0.4-0.6 mm. Late ignition (4-8 "to V. M. T.) is provided during assembly at the factory by installing the breaker body in a certain position, and the desired ignition timing (maximum - 32-36" to V. M. T.) is regulated by the owner of the machine himself by turning the breaker disk with a shifter mounted on the steering wheel. It is impossible to mount a breaker type PM-302 with an ignition timing device on the engine, as this is due to alterations of the camshaft and the front cover of the engine. To check the setting of the ignition timing, the engine flywheel is marked with the letters "B" (top dead center), "P" ( early ignition) and "II" (late ignition), which are visible in the viewing window located near the oil filler neck. When the “P” mark is combined with the installation risk, the ignition timing along the crankshaft is 32-36 ° to the top dead center, and the piston is at a distance of 7.0 mm from the upper extreme position (top dead center). The engine is running normally motor gasoline A-72 or A-76 (GOST 2084-67). You cannot use fuel with a lower octane rating, such as A-66. Interchangeability of engines and parts. Motorcycle engines K-650 "Dnepr", K-750M and M-63 are completely non-interchangeable. In addition to the rings, which we have already talked about, these engines have an interchangeable piston pin, camshaft and generator gears, and a generator gasket. camshaft oil seal and all clutch parts. With the M-63, the Dnepr also has interchangeable valve springs (outer and inner) and valve spring plates (upper and lower). The design of the K-650 engine, its proper operation and systematic maintenance ensure reliable operation and a long service life. N. OVCHARENKO, Head of the Engine Department of the Kyiv Motorcycle Plant, Also on topic
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