In detail: do-it-yourself repair of a snowmobile Buran 640 from a real master for the site my.housecope.com.
The RMZ-640 "Buran" engine produced by the Rybinsk Motor-Building Plant is widely used not only on the snowmobiles of the same name, but also on deltalets. However, if individual snowmobile owners are satisfied with its characteristics to some extent, then pilots - with rare exceptions. And many of those who deal with RMZ for a long time are aware of the constant threat of cylinder overheating and piston burnout. Therefore, delta pilots are trying to replace the "six hundred and forty" engine with a better one, if possible with an imported one, or, at worst, improve it.
In general, they have few ways of improvement: either to improve the existing structure in detail, or to remodel it on a large scale. The most decisive go for a deep modernization, affecting the main systems of the Rybinsk motor. Regular readers of our magazine know examples of such modernization. The most famous, dating back to the fall of 1996, is given in the publications "Beetle-42: Transport for Heaven and Earth" (Modelist-Constructor No. 8,9,11 ’96). Anatoly Zhukov, the designer of the Zhuk deltaplane, increased the power of the 600th by equipping its cylinders with individual carburetors and mufflers. He solved the temperature problem radically by converting the engine from air to liquid cooling.
However, the reserves of the standard RMZ-640 are far from being exhausted. Many designers are engaged in the opening of these reserves: in Rybinsk, in the factory design bureau, and in other cities, in flying clubs, various laboratories and scientific and technical centers. Valery NOVOSELTSEV, an employee of the Moscow Scientific and Technical Center “Istok”, presents his version of improving the performance of the famous engine.
Video (click to play).
The article describes the work on the modernization of the RMZ-640 "Buran". The participants set themselves the task of improving the performance of a widely used engine. One of the main activities to accomplish this task was to refine the design of plate check valves.
In our case, we used a serial engine with serial number 88410219, which had previously worked on a two-seat deltaplane for 46 hours. The declared power of this engine is 28 hp. at 5500 rpm. It is equipped with a V-belt reducer with a gear ratio of 1: 2.15, a propeller with a diameter of 1.6 m and a pitch of 0.79 m, as well as standard A17DV candles and a K-62Zh carburetor with a diffuser diameter of 32 mm and a main jet with a diameter of 1.36 mm.
The engine ran on fuel consisting of a mixture of AI-93 gasoline (specific gravity 0.74) and MGD-14M oil in a ratio of 1:30. Fuel was supplied by gravity from a supply tank installed at a height of 2.5 m relative to the carburetor.
Before the tests, the valve timing was checked, the effective compression ratio was refined - it was Eef = 5.6. A low value of the average effective pressure of the serial engine was noted - only 3.56 kg / cm2.
All operations related to the removal of characteristics were carried out on a complex engine test bench made in the aviation department of the Scientific and Technical Center "Istok" and which made it possible to simultaneously register the values of torque, fuel consumption, speed and temperature of the cylinder heads.
The stand includes a balancing machine, a moulinette (wooden propeller with a diameter of 840 mm), a fuel flow meter (shtihprober) with hermetically sealed contacts (reed switches), a thermocouple with a dial indicator, and a fuel tank with a capacity of 10 liters.
To change the moment of resistance, six pairs of replaceable brake plates were attached to the ends of the moulinette blades, which made it possible to obtain seven points for measuring the parameters of the external characteristic.
The measuring base of the gauge consisted of three volumes controlled by reed switches, a magnetic float and three-way valves. Electronic tachometer - contactless, with an induction sensor. Temperature meter - aviation, registering the temperature of the cylinder heads under the spark plug.
To reduce frictional forces, all movable joints of the machine are equipped with rolling bearings.
The work was carried out in four stages:
1) taking the initial (control) characteristics of the serial engine;
3) taking the characteristics of the upgraded engine and checking it over on a hang-glider;
4) taking the characteristics of the upgraded engine without a blower and gearbox.
The first stage was carried out on a complex motor test bench.
Rice. 1. Units and parts of the serial engine RMZ-640 "Buran", which were re-manufactured or modernized.
Rice. 2. Modified inlet (a) and outlet (b) cylinder windows (the cylinder surface is deployed in the plane of the drawing).
Rice. 3. Modified piston (the surface of the piston is deployed in the plane of the drawing).
Test conditions: outside air temperature + 2 ° С; atmospheric pressure - 746 mm Hg; fuel - a mixture of AI-93 gasoline with MGD-14M oil (1:30); carburetor - К-62Ж (main jet diameter - 1.36 mm; effective compression ratio Eef = 5.6); candles - А17ДВ.
The following results were obtained.
Propeller characteristic (external load - propeller with a diameter
1.6 m at 0.79 m steps): Ne = 25.8 HP at 5086 rpm, Ce = 0.433 kg / h HP
External characteristic (external load - moulinette): Ne = 27.9 HP at 5514 rpm, Ce = 0.416 kg / h HP Head temperature t ° C = 212 ° C.
The second stage is the actual modernization. Have undergone revision; crankcase (displacers are installed in the corners of the crank chamber), cylinder heads (the bearing surfaces of the heads are cut by
1.8 mm to increase the effective compression ratio, Eef increased to 7.2, the cylinders themselves (the intake and exhaust ports are bored), the crankshaft (displacers are installed in the cheek grooves), the cuffs of the crankshaft main journals (cut by 1 mm). The carburetor diffuser was also bored to a diameter of 33.6 mm, the diameter of the main jet was increased to 2.12 mm, and the height of the nozzle was reduced by 0.76 mm.
The valve timing (intake and exhaust) is increased. Each cylinder has two additional bypass channels with phases equal to the phases of the main channels (the cylinder liner was not pressed out in this case).
Made anew; pistons, valve box, box cover, plate check valves (plates, seats and stops), cuff clips.
The pistons are forged from AK12D alloy. They have two purge ports each, which lowered the temperature of the upper rings and piston heads and excluded burnout.
Unlike the serial piston, the skirt of the new piston is barrel-shaped and elliptical in accordance with the temperature gradient. The geometry of the skirt was adjusted experimentally. Since this process is rather complicated, it is possible to leave the standard pistons as well, modifying them according to the attached drawings.
The body and cover of the box of plate check valves are cast from АЛ1. However, it is possible to use any other cast heat-treatable aluminum alloy.
The valve seats are made by pressing from organite (or Kevlar, as this SVM is also called - ultra-high-strength material) on an epoxy binder heated to 80-85 ° C during the polymerization process. Saddle sizes with minor changes are taken from the book by V.M. Kondrashev and others (see Literature).The material of the valve plates is STEF-1 fiberglass, the stoppers are steel.
Since the placement of the valves and the bore of the cylinder windows increase the volume of the crankcase by 41 cm3 (which leads to a decrease in the purge pressure and, as a result, to a decrease in the maximum engine power), so-called displacers are installed in the grooves of the crankshaft cheeks and in the corners of the crankcase harmful volume. On the crankshaft, they are made of glass thread on an epoxy binder (for better adhesion of the winding to the cheeks with a drill with a diameter of 4 mm, holes with a depth of 0.5 mm are marked in them). In the crankcase, the displacers are aluminum half-rings of triangular cross-section, fastened with M4 screws.
The sum of the displaced volume in the chamber together with the volume displaced by the cuff yoke is 79 cm3, which more than compensates for the increase in volume from valve placement and window boring, which ultimately improves blowdown.
However, the increase in pressure in the crankcase led to the fact that the standard cuffs began to be squeezed out of the clips. This was revealed during the first engine starts. I had to make new clips and install in them cuffs from the axle shafts of the VAZ-2101 car, cut by 1 mm and facing each other with the front side. To seal the clips, rubber rings from the ignition shaft from the engine of a VAZ-2108 car were used.
Before mounting the cuffs, the clips were heated to 200-250 ° C. Then, TsIATIM-201 grease with molybdenum disulfite was stuffed in the cuff cavity, after which the clips were mounted on the crankshaft. Their shoulders are tucked into the crankcase recesses, and the standard thrust rings are dismantled.
In addition to these works, the usual two-stroke ICE procedures were carried out to refine the inner surfaces, that is, cleaning the casting in channels and windows and adjusting the mating lines of the crankcase and cylinders. More about this in the book of IM Grigoriev (see Literature).
Stage three. During repeated tests, the parameters of the external, screw, flow characteristics and the maximum temperature of the cylinder head under the spark plug were measured. The temperature and composition of the exhaust gases were not indicated. The power was brought back to normal conditions. The ignition system has not been changed or adjusted.
Test conditions: outside air temperature - 8 ° С; atmospheric pressure - 748 mm Hg; fuel and external load are the same as before the upgrade; the carburetor diffuser is bored to a diameter of 33.6 mm; main jet - up to a diameter of 2.12 mm; Eef = 7.2.
Results of tests of the upgraded engine.
Propeller characteristic: Ne = 31.7 h.p. at 5316 rpm, Ce = 0.321 kg / h HP; head temperature t ° Cmax = 204 ° C; increase in capacity - 22.8 percent, efficiency - 25.8 percent.
External characteristic: Ne = 38.2 hp at 5778 rpm, Ce = 0.332 kg / h HP Head temperature - t ° Сmax = 208 ° С; increase in capacity - 36.9 percent, efficiency - 20.25 percent.
And finally, the fourth stage. In the configuration without a gearbox and a blower, the engine spun up to 6840 rpm, the recorded power was 19.6 hp, Ce = 42.2 hp. at 5978 rpm, Ce = 0.338 kg / h HP
For the characteristics of the modernized engine, a new propeller with a Wortman profile RH-63-137 with a diameter of 1.6 m and a pitch of 0.8 m was designed and manufactured for a flight speed of 72 km / h. With him on the mooring lines, a thrust of 152 kg was obtained. Prior to this, the thrust on the mooring serial engine with a standard propeller reached 112 kg, after modernization - 135 kg.
The rate of climb of a two-seater hang-glider with a serial engine and a standard propeller was 1 m / s. After modernization, with the same propeller, - 2.5-2.8 m / s; and with the newly manufactured - 3-3.2 m / s, while the hourly fuel consumption did not exceed 9 liters.
The temperature of the head of the "hot" cylinder of the modernized engine during take-off and climb operation at an outside air temperature of + 28 ° C did not exceed 195 ° C.
Bottom line: after completing the listed stages of modernization, the engine's operation became smoother and smoother, starting was much easier. Almost all of its main characteristics have improved: power, efficiency, continuity and, most importantly, reliability. At the end of September 1999, the engine worked 32 hours in deltaplane flights without any remarks.
2. Grigoriev I.M. A motorcycle without secrets. - M., DOSAAF, 1973.
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Took the following 1. I made grooves in the pistons in the part of the groove for a specific thickness of the rings 2. Changed the geometry of the chamfers, now the protruding part locks the ring in the groove and when the chamfer presses it simply has nowhere to go 3. On the insistent advice of a member of the forum (Dad) cut the retaining rings upward, it is possible and downward only supposedly not from the side. The logic seems to be seen on the basis of shock loads
These improvements will in no way go to a minus, only to a plus, and what a plus will winter show
