Engine PMZ-640: device, modernization

РМЗ-640 "Buran" is a two-stroke 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 rectilinear reciprocating motion of the pistons into the rotation of the crankshaft.

In this article, every detail of the gearbox will be considered separately.

Crankshaft arrangement

The three-bearing crankshaft includes 46 trunnions on the right side and 23 pivots on the left side, 8 cheeks with a crank pin and 49 medium shafts, the connection of which is provided with press fitings. As a support mechanism are three ball bearings that are mounted on the middle shaft and journal journals. The rings in the grooves of the cages outside the bearings and labyrinth seals are designed to equalize the loads imposed on the crankshaft bearing bearings .

The movement of the part along the axis is held by the bearing of the bearings that are aimed at the locking rings. They are located in certain grooves of the crankcase. Sealing of the ends of the part is provided with a spiral bracelet spring.

Connecting rods

The connecting rod of the engine serves to connect the piston with the crankshaft. The main component of the workpiece is the head on top, as well as the crank head located at the bottom. They are connected by a rod with an I-section.

The connecting rod of the engine includes an upper and a lower head provided with holes. They are equipped with needle bearings. The radial clearance is from 0.012 to 0.024 mm. The clearance is provided by sorting by diameter (based on different sizes of bearing rollers, piston and crank fingers). The group marking is indicated on the stem part under the head. The holes under the connecting rod serve as lubrication of the bearings.

Piston rings

Pistons are present in the engine design. 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 ring can be used in the circuit with a cross-section in the form of a trapezoid and a rectangle.

There is a thermal gap in the back of the ring. During operation, it is subject to expansion from heating. After installation, the gap diameter for rings with a trapezoidal section is 0.40 to 0.55 mm. To obtain such dimensions, it is possible to saw the end parts of the lock.

The gap between the ends and grooves when the ring is compressed to a diameter of 76 mm should be 0.06-0.15 mm for a trapezoidal section and 0.080-0.115 mm for a section in the form of a rectangle.

The locking ring functions at high temperature. The oil that enters the gap between the hot ring and the piston groove is subjected to coking. In other words, the formation of carbon deposits and the deposition of resinous substances occur, which causes burning of the rings. This contributes to a deterioration in the starting parameters and a decrease in the power level of the unit

If the deposit is not removed in a timely manner, the device may deteriorate. A greater propensity to burn is noted near the upper ring. Burning, as a rule, is provoked by overheating of the engine when it is misused, and also because of the failure of the cylinder and ring.

Purpose of the piston pin

The piston pin serves to connect the piston and connecting rod on the hinges. Based on the outside diameter, the piston pins are divided into two sizes. The group is marked with a white or black color on the end of the part. When assembling, the fingers are selected with the same marks.

Structure of cylinders

Cylinders do not replace each other. Their basis is a shirt made of aluminum, into which a sleeve of cast iron is pressed. To ensure a selective assembly of the interface between the sleeve and the piston, the cylinders are produced in three sizes. The indicators are marked with the letters "M", "C", "B". They are applied by impact method to the flanges of the cylinder flange, which is located from the bottom. When replacing a cylinder, a detail of the same size is placed.

The cylinder is mounted on the crankcase with a lower flange. On the flange, located on top, the cylinder head is installed. Between the head and the cylinder is laid a gasket of asbestos. When the bulkheads of the unit, this gasket can be used again.

The joint of the lower flange of the cylinder and the reference plane of the crankcase is sealed by means of a paronite. Mounting of each crankcase on the cylinder is provided by four pins.

Cylinder Head Construction

The basis of the cylinder heads is an alloy of aluminum. The base of the combustion chamber head is equipped with a threaded hole for mounting the spark plug. To avoid deformation of the head and cylinder, when assembling the nut of the stud, tighten crosswise twice. First, a preliminary tightening is carried out, and then the final one is 2.0-2.5 kgf-m.

It should be noted that the nuts of the exhaust manifold must first be secured. Tightening and tightening nuts is carried out on a cold unit.

Carter

Carter acts as the main body of the engine. It consists of two parts, which are made of aluminum. Between themselves, the halves are attached by means of pins screwed into the upper part. The fastening nuts are tightened with a torque of 3.0-3.5 kgf-m.

Both parts of the crankcase are subjected to parallel processing and therefore do not replace each other. Each cylinder with a head is fixed to the crankcase by means of four pins, which are screwed into the thread of the support flange. The plane of the connector is greased.

The ends of the crankshaft, which come out of the crank chambers, are sealed with movable cuffs. The isolation of the crank chambers is made with the help of labyrinth seals installed along the middle of the middle bearing.

How does the engine cool down?

At the engine system in operation, the temperature of the heads should not be above 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 at the required rate. To solve this problem, an air cooling system is used, consisting of an axial blower and a blow-out casing.

The base of the fan is the impeller, which is planted in a fixed position on the platen. In the housing, the impeller is mounted on a pair of ball bearings that have a double-sided seal. At the factory they are filled with working lubricant.

The impeller functions with the aid of a V-belt from the drive pulley. It is fixed on three stiletto heels. At the end of the roller is a driven pulley, which consists of a pair of profiled semi-washer discs. The tightening of the pulley attachment nut is carried out with a torque of 5-6 kgf-m.

The body is mounted on four flange studs to the right of the crankcase. At the fan inlet, a device for collecting air from the plastic is mounted. The belt tension is carried out by changing the adjustment washers, which are located between the half-shells.

The vertex of the stream's angle shifts from the center. This increases the diameter of the driven pulley and the belt tension. When using the engine, always check the tension of the fan belt. Under the force with an index of 4 ± 0.5 kgf, the bending index of the belt should be 6-15 mm. A very weak index of tension causes slipping of the belt at high speeds. Its stratification from heating and strong tension spoil the bearings of the impeller. It should not be allowed to hit the grease on the belt, as this contributes to its destruction and provokes a malfunction.

How is the power system arranged?

It includes the following elements:

• Fuel tank;
• Intake filter;
• Filter settler;
• Hand pump for pumping;
• Carburetor with fuel pump;
• Air cleaner.

Modernization

The engine of the RMZ-640 has a large reserve of liter capacity. If you make the design of a rigid crankcase correctly, mount the bearings of the knee shaft to bearings and make engine components from high-quality materials, then, according to experts, this unit can produce at least 62 liters. from.

What measures are taken to increase the power of the device?

To increase the power level of such a device as the РМЗ-640 reducer, it is recommended to perform the following manipulations:

• Replace the oil seal of the knee shaft with other modifications (take seal from "Moskvich-412").
• To make a new stuffing box with the use of material D16T or its analog.
• Drill additional channels for ventilation.
• Install an additional pair of medium-sized bearings instead of one on the knee shaft between the middle flywheels.
• Install the deflectors between the cylinders at the airflow outlet.
• Balancing pistons with a difference in weight is not more than 1.5 g.
• Provide thermal insulation of the collector for exhaust via an asbestos cord.
• To establish cylinders on height so that edges of final and inlet windows of the cylinder coincided with edges of a skirt and the piston bottom. So the phases of air release on both cylinders will coincide.
• Mount the resonant tube with a noise barrier.

How to improve the functionality of the crankcase?

The cause of the deformation of the crankcase is the weakness of its stiffness and the greater knee joint stability 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 knee shaft in the crankcase. In this case, the bearings do not have a gap. The knee shaft expands when heated, and the required clearance is absent, so the bearing jams. 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 must be mounted, and an oil seal must be installed between them.

Vibration of the shaft brackets without the necessary lubrication causes the shaft seals to be erased. Overheating causes their compaction. The result is a breakthrough of air through the stuffing box and depletion of the mixture of fuel and air in the engine casing. The consequences will be very deplorable - the piston will melt or its bottom will melt. The device RMZ-640 will jam.

What should I do to improve the blowing?

To optimize the inflation of the cylinder from the rear, additional deflectors should be installed, which form the blowing of each cylinder with its cold airflow. The cylinder, located at the front, does not heat the rear. The additional winding of the exhaust manifold with an asbestos cord on the silicate glue also provides less heat to the air driven by the fan to the cylinders.

How to solve the problem of unbalanced pistons?

The difference in weight of pistons on average by 20 g is caused by insufficient reasonableness of details of the unit. This imbalance becomes the culprit for the disturbance of smooth and steady operation of the engine, which causes a high level of vibration. To fit the piston by weight, remove the excess layer of metal from the inside of the skirt, adjust it to the size of the bypass window in the skirt with the cylinder windows (their coincidence must be achieved). It is necessary to round the radii at the ends of the windows, as well as to remove the bevels with a radius of 0.5 mm.

An important role is played by the fact that the coordination of the operation of the cylinders and the reduction in engine vibration is influenced by the correct installation of the inlet and outlet phases of the mixture from the air. This is easy enough. It is necessary to lay an additional gasket under the cylinder, which is located from the bottom. It will be better if the bottom of the piston coincides with the bottom edge of the cylinder window at the exit. It is recommended to install a resonant tube and a silencer.

By adjusting the carburetor and making some improvements in electronics and ignition, you will get a unit whose operation will differ in stability, uniformity and economical fuel consumption. The indicator of the temperature regime at maximum revolutions beneath the candle of the cylinder located behind varies in the range of 190 ° C. The revolutions of the knee shaft of the unit during take-off are from 4700 rpm to 5200 rpm.

How to make improvements in the field of electronics and ignition?

• Screws fixing the plates of iron magdino to the magnets must be made of brass. Mounting them must be reliable. If the small screw is loosened, the unit will not operate properly.
• Balancing the Muggino must be of high quality. It is also produced after the factory setting, since it contributes to optimum vibration. A good balancing requires a fan for blowing.
• The coil leads must be soldered. Their screws must be made of stainless steel or covered with oxide. Before their twisting by means of a tap it is recommended to improve a condition of a carving in a fixed part of a magdino. On the trowel there is a lot of trash. This is the reason for poor grounding. Places of contact of the terminals of the coils with fixing screws also need soldering.
• After screwing the coils to the base of the magdino, all areas of contacts and rations must be covered with a sealant.
• It is recommended to remove an additional wire for grounding the ignition coil under the candles.
• High-voltage wires are not taken from an old car. For example, the NGK series candles are suitable.
• Ignition should be carried out on the factory label. The fixing bolts must be well-balanced for the safety of the ignition angle.
• If in the design of the Buran engine add a gear reducer with a transmission ratio of 2.2-2.6 m and complete the unit with a two-bladed propeller 1.65-1.8 m or a three-lobed model 1.45-1.6 m, Get a quality traction, characterized by stability.

Complete the original device

The original units of the RMZ-640 are stuffed with pistons and piston rings produced in the Czech Republic. Needle bearings are available in Japan. In the counterfeit unit RMZ-640, spare parts are manufactured in China. Such an aggregate does not have a high degree of functionality.

Of course, by purchasing the Buran engine, it is difficult to see how its mechanism is assembled, so it is recommended that you pay attention to the following:

• The engine produced at the plant is supplied to dealers and to stores in a branded box made of cardboard with the "RM" logo.
• The package must bear the company logo containing the serial number of the unit.
• The device must be accompanied by a technical passport. The number registered in it must match the number indicated on the device itself.
• "Buran 640" contains in the body convex logos "RM". Brand marks can be seen on the casing of a manual starter or the fan casing.
• Pay attention to the base located under the motor. From the units of RMZ-640, which began to be produced after February 2013, this detail was withdrawn.

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 the units that are in operation is ensured by the purchase of parts and repair by their own hands. A major disadvantage, complicating the use of this device, can be considered a deficit of spare parts. They are mainly delivered in Rybinsk, as the reducer is used for snowmobile "Buran". Also a major omission is that no special literature was 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 is widely used in small aircraft. Many fans buy a box of RMZ spare parts. It costs seven times cheaper than the specialized reduction gear "Buran-Avia". Cheapness and 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 regress of setting up the release of special equipment for aircraft, which has an acceptable price.

Low-income and non-compliant aviation lovers will not use a specialized engine as long as it is possible to assemble an analogue at a low price.