RMZ-640 “Buran” is a push-pull configuration. Contains a crank-chamber purge equipped with a carburetor. It contains a two-cylinder engine.
The purpose of the crank mechanism, which is the basis of the engine, is to convert the linear reciprocating motion of the pistons into the rotation of the crankshaft.
In this article, each detail of the gearbox will be considered separately.
Crankshaft device
The three-support crankshaft includes 46 trunnions on the right side and 23 trunnions on the left side, 8 cheeks with a crank pin and 49 middle shafts, the connection of which is ensured by press fittings. Three ball bearings, which are mounted on the middle shaft and the journal journals, act as a support for the mechanism. The rings located in the grooves of the cages outside the bearings and labyrinth type seals are designed to equalize the loads placed on the bearings of the crankshaft.
The movement of the part along the axis is held by the emphasis of the bearings directed into the snap rings. They are located in certain crankcase grooves. The sealing of the ends of the part is provided by a spiral bracelet spring.
Connecting rods
The connecting rod of the engine is used to connect the piston with the crankshaft. The main component of the part is the head located on top, as well as the crank head located on the bottom. They are connected by a rod with an I-section.
The connecting rod of the engine includes an upper and lower head provided with holes. Needle bearings are mounted in them. The radial clearance index is from 0.012 to 0.024 mm. The clearance is ensured by sorting by diameter (based on different sizes of bearing rollers, piston and crank pins). The marking of the group is indicated on the rod part under the head. The holes under the connecting rod are used to lubricate the bearings.
Piston rings
The engine design contains pistons. They do not replace each other. They are mounted on a pair of piston rings, the basis of which is wear-resistant cast iron. A snap ring with a section in the shape of a trapezoid and a rectangle can be used in the circuit.
There is a thermal gap at the back of the ring. During operation, it undergoes expansion from heat. After installation, the gap diameter for rings with a section in the form of a trapezoid is from 0.40 to 0.55 mm. To obtain such dimensions, it is possible to file the end parts of the lock.
The gap between the ends and grooves when compressing the ring to a diameter of 76 mm should be 0.06-0.15 mm for a section in the shape of a trapezoid and 0.080-0.115 mm for a section in the shape of a rectangle.
Circlip operates at high temperature. Oil falling into the gap between the hot ring and the piston groove is coked. In other words, the formation of soot and the deposition of resinous substances occurs, which causes burning of the rings. This contributes to the deterioration of starting performance and lower power level of the unit
If the deposit is not removed in a timely manner, the device may deteriorate. A greater tendency to stick is noted at the upper ring. Burning, as a rule, is provoked from overheating of the engine during its improper use, as well as due to failure of the cylinder and ring.
The purpose of the piston pin
The piston pin is used to connect on the hinges of the piston and connecting rod. Based on the indicator of the outer diameter, the piston fingers are divided into two sizes. The group is marked in white or black at the end of the part. When assembling, fingers are selected with the same marks.
Cylinder structure
Cylinders do not replace each other. They are based on an aluminum shirt with a cast-iron sleeve pressed into it. To ensure selective assembly of the interface between the liner and the piston, the cylinders are made in three sizes. Indicators are marked with the letters "M", "C", "B". They are applied by shock to the flange of the cylinder bottom. When replacing a cylinder, a part of the same size is placed.
The cylinder is mounted on the crankcase with the bottom flange. A cylinder head is mounted on the top flange. A gasket made of asbestos is laid between the head and the cylinder. When the bulkheads of the unit, this gasket can be reused.
The joint of the lower flange of the cylinder and the supporting plane of the crankcase is sealed with paronite. The mounting of each crankcase on the cylinder is provided with four studs.
Cylinder head design
The basis of the cylinder heads is an alloy of aluminum. The base of the head of the combustion chamber is equipped with a threaded hole for mounting the spark plug. To avoid deformation of the head and cylinder, when assembling the stud nut, tighten crosswise twice. First, preliminary tightening is carried out, and then final to 2.0-2.5 kgf-m.
It should be noted that the nuts of the exhaust manifold should be fixed first. Tightening and tightening the nuts is carried out on a cold unit.
Carter
Carter acts as the main engine body part. It consists of two parts, which are made of aluminum. Between themselves, the halves are attached by means of studs screwed into the upper part. The fastening nuts are tightened with a moment indicator of 3.0-3.5 kgf-m.
Both parts of the crankcase undergo parallel processing and therefore do not replace each other. Each cylinder with a head is fixed to the crankcase by means of four studs, which are screwed into the thread of the support flange. The connector plane of the part is greased with sealant.
The ends of the crankshaft that exit the crank chambers are sealed with movable cuffs. The isolation of the crank chambers was made using labyrinth seals installed on both ends of the middle support bearing.
How does the engine cool down?
For an engine system in operation, the head temperature should not be higher than 200 ° C.
Since the unit is closed by a hood, cooling it with air flows through the grilles is not enough to maintain the temperature level in the right rate. To solve this problem, an air cooling system is used, consisting of an axial discharge fan and a blower casing.
The basis of the fan is the impeller, which is planted in a fixed position on the roller. In the housing, the impeller is mounted on a pair of ball bearings, which have a double-sided seal. At the factory they are filled with working lubricant.
The impeller operates with the assistance of the V-belt from the drive pulley. It is mounted on three stilettos. At the end of the roller is a driven pulley, which consists of a pair of profiled half-screw disks. The pulley fastening nut was tightened with a torque of 5-6 kgf-m.
The housing is mounted on four flange studs to the right of the crankcase. At the fan inlet, a device for air intake from plastic is mounted. The tension of the belt is due to the rearrangement of the adjustment washers, which are located between the half-gears.
The top of the angle of the stream is shifted from the center. Thus, it increases the diameter of the driven pulley and the belt tension. When using the engine, constantly check the fan belt tension. Under a force of 4 ± 0.5 kgf, the belt flexion should be 6-15 mm. A very weak tension indicator causes the belt to slip at high speeds. Its delamination from heating and strong tension spoils the impeller bearings. The lubricant must not be allowed to hit the belt, as this contributes to its destruction and provokes a malfunction.
How is the power system?
It includes the following elements:
- fuel tank;
- intake filter;
- sediment filter;
- manual booster pump;
- carburetor with fuel pump;
- air purifier.
Modernization
The RMZ-640 engine has a large stock of displacement capacity. If the hard crankcase is correctly constructed, the crankshaft bearings are mounted on bearings and the engine components are made of high quality materials, then, according to experts, this unit can produce at least 62 liters. from.
What events are held to increase the power of the device?
In order to increase the power level of a device such as a PMZ-640 gearbox, it is recommended to carry out the following manipulations:
- Replace the crankshaft oil seals with other modifications (an oil seal from Moskvich-412 is taken).
- To make a new stuffing box using material D16T or its analogue.
- Drill additional ventilation ducts.
- Install an additional pair of medium-sized bearings instead of one on the crankshaft between the middle flywheels.
- Install deflectors between the cylinders at the air outlet.
- Balance pistons with a difference in weight of not more than 1.5 g.
- Provide thermal insulation to the exhaust manifold using an asbestos cord.
- Set the cylinders in height so that the edges of the exhaust and inlet windows of the cylinder coincide with the edges of the skirt and piston bottom. So the phases of the air release on both cylinders coincide.
- Mount a resonant tube with a noise screen.
How to improve crankcase functionality?
The cause of the crankcase deformation is the weakness of its rigidity and the large cantileverness of the crankshaft between the three supports. This causes an increased load on the bearings, which, without proper lubrication, contribute to increased resistance, rolling and friction.
The same effect is caused by the retaining rings of the bearings from the displacement of the crankshaft in the crankcase. In this case, the bearings have no clearance. When heating the knee shaft expands, and the required clearance is absent, therefore the bearing wedges. The knee shaft begins to overheat and is not able to develop the required speed. For optimal functioning of the part, a pair of bearings should be mounted, and an oil seal should be installed between them.
Vibration of the shaft consoles without the necessary lubrication erases the crankshaft oil seals. Overheating causes them to condense. The result is a breakthrough of air through the oil seal and a lean mixture of fuel and air in the engine crankcase. The consequences will be very deplorable - the piston burns out or its bottom melts. The RMZ-640 device will jam.
What to do to improve blowing?
To optimize the blowing of the rear cylinder, additional deflectors should be installed, which form a blowing of each cylinder with its cold air flow. A cylinder located on the front does not heat the rear. An additional winding of the exhaust manifold with an asbestos cord on silicate glue also provides less heating of the air driven by the fan to the cylinders.
How to solve the problem of unbalanced pistons?
The difference in the weight of the pistons by an average of 20 g is caused by the lack of thought over the details of the unit. This imbalance becomes the culprit in disturbing the smooth and stable operation of the engine, which causes a high level of vibration. To adjust the weight of the piston, an excess metal layer should be removed from the inside of the skirt, adjusted to the size of the bypass window in the skirt and the cylinder windows (their coincidence must be achieved). It is necessary to carry out the rounding of radii at the ends of the windows, as well as the dismantling of the bevels with a radius of 0.5 mm.
An important role is played by the fact that the correct installation of the intake and exhaust phases of the mixture from the air affects the coherence of the cylinders and the reduction of engine vibration. This is easy enough to do. It is necessary to lay an additional gasket under the cylinder, which is located below. It will be better if the bottom of the piston coincides with the lower edge of the cylinder window at the outlet. The installation of a resonance tube and silencer is recommended.
After adjusting the carburetor and making some improvements in electronics and ignition, you will get a unit whose work will be distinguished by stability, uniformity and economical fuel consumption. The temperature indicator at maximum speeds under the candle of the cylinder located at the rear fluctuates in the range of 190 ° C. The revolutions of the knee shaft of the unit during take-off have an indicator from 4700 rpm to 5200 rpm.
How to make improvements in the field of electronics and ignition?
- The screws holding the magdino iron plates to the magnets should be made of brass. Their fastening should be reliable. If at least one small screw is loosened, the unit will not function properly.
- Mardino balancing should be of high quality. It is also made after the factory setting, as it contributes to optimal vibration. Good fan balancing is also required.
- The leads of the coils must be brazed. Their screws must be made of stainless steel or coated with oxide. Before twisting them with a tap, it is recommended to improve the condition of the thread in the fixed part of the magdino. There is a lot of trash left on the tap. This is the reason for poor grounding. The contact points of the coil terminals with the fixing screws also need soldering.
- After screwing the coils to the base of the magdino, all contact areas and rations must be covered with sealant.
- It is recommended to lay an additional wire for grounding the ignition coil under the candles.
- High-voltage wires are not taken from an old car. For example, NGK series candles are suitable.
- Ignition should be carried out at the factory mark. The fixing bolts must be well locked to maintain the ignition angle.
- If you add a gear reducer with a transmission ratio of 2.2-2.6 m to the Buran engine design and supplement the unit with a two-blade propeller of 1.65-1.8 m or a three-blade model of 1.45-1.6 m, then get high-quality traction, characterized by stability.
Original equipment
The original units of the RMZ-640 are filled with pistons and piston rings manufactured in the Czech Republic. Needle bearings are available in Japan. In the fake RMZ-640 unit, spare parts are manufactured in China. Such an aggregate does not have a high degree of functionality.
Of course, when acquiring the Buran engine, it is difficult to consider how its mechanism is assembled, so it is recommended to pay attention to the following:
- The engine produced at the factory is delivered to dealers and stores in a company cardboard box with the "PM" logo.
- The packaging must bear the company logo containing the serial number of the unit.
- A technical data sheet must be attached to the device. The number written in it must match the number indicated on the device itself.
- "Buran 640" contains convex logos "PM" in the case. Brand names can be seen on the manual starter case or on the fan housing.
- Pay attention to the base located under the motor. This part was removed from the units of the RMZ-640, which began to be produced after February 2013.
Difficulties in engine operation
The unit, specially created for the snowmobile, has a high level of functionality. In this article, the main characteristics of the RMZ-640 engine were considered.
Currently, the operating condition of units that are in operation is ensured by the purchase of parts and DIY repair. A big minus that complicates the use of this device is the lack of spare parts. They get mainly in Rybinsk, as the gearbox is used for the Buran snowmobile. Also a big omission is that no special literature has been published on the use, repair and maintenance of the product.
Application of the unit in small aircraft
The modified design of the Buran RMZ-640 device is widely used in small aircraft. Many amateurs purchase a “box” of RMZ for parts. It costs seven times cheaper than the specialized Buran-Avia gearbox. Cheapness is the main reason for using the model RMZ-640.
Of course, the level of assembly and modernization depends on the skills of a particular person, but the use of the unit in aviation is not a positive trend. It leads to a regression in arranging the production of special equipment for aircraft, which has an affordable price.
Poor and non-compliance aviation enthusiasts will not use a specialized engine as long as it is possible to assemble an analog at a low price.