The engine RMZ-640 “Buran” Rybinsk engine production plant is widely used not only on the same snowmobile, but deltalyo. However, if a separate snowmobile owners its characteristics in some way satisfied, then the pilots — with a few exceptions. And the constant threat of overheating of the cylinders and pistons burnout know many people who for a long time dealing with RMZ. So deltaleft trying to replace “shestistrunnoi” engine better, possibly imported or, at worst, to improve.

Ways to improve them, in General, is a bit: either to improve an existing design in detail, or to alter big. The most decisive go on a deep modernization, affecting the major systems of the Rybinsk motor. Regular readers of our magazine know examples of such modernization. The most famous relating to the fall of 1996, given in the publications of “beetle-42: transport to heaven and earth” (“modelist-Konstruktor” No. 8,9,11 ’96). Anatoly Zhukov, the designer ultralights “beetle” raised power “shestistrunnoi”, providing it the cylinders are individual carburetors and mufflers. Temperature same problem he decided to radically modifying the engine with the air to liquid cooling.
However, the reserves RMZ-640 regular complete is far from exhausted. The opening of these reserves is being done by many designers in Rybinsk— KB in the factory and in other cities in Aero clubs, various laboratories and scientific-technical centers. The employee of the Moscow STC “Istok” Valery NOVOSELTSEV is your option of improving performance of the known motor.
The article describes the work on modernization of the RMZ-640 “Buran”. The participants were set a task to improve the performance of the widely used engine. One of the main activities for the implementation of this task was to test design back plate valves.
In our case, we use the serial engine serial No. 88410219 that has worked before on double deltalat 46 hours. The stated plant capacity of this engine is 28 HP at 5500 rpm. It is equipped with a V-belt reducer with the transmission ratio 1:2,15, a propeller with a diameter of 1.6 m and pitch of 0.79 m, and standard plugs А17ДВ and carb-TO-62Ж with a cone diameter of 32 mm and a channel of the main nozzle with a diameter of 1.36 mm.
The engine was running on fuel consisting of a mixture of gasoline AI-93 (the proportion of 0.74) and oil MHD-14M in the ratio of 1:30. Fuel received by gravity from a feed tank that is installed at a height of 2.5 m relative to the carb.
Before the tests was checked the timing, adjusted the effective compression ratio — it amounted to the value of EF = 5,6. Highlighted the low value of the average effective pressure series motor — 3,56 kg/cm2.
All operations associated with the removal characteristics was conducted on the integrated engine stand made in the aviation Department of the Scientific-technical center “the Source” and allows you to simultaneously record torque, fuel consumption, rpm and temperatures of the cylinder heads.
The stand includes a beam machine, molinetto (wooden propeller with a diameter of 840 mm) fuel flow meter (stichproben) with sealed contacts (reed switches), the thermocouple with a needle indicator and expendable fuel tank capacity of 10 liters.
To change the torque on the ends of the blades moulinette were fastened with six pairs of replacement brake plates, which allowed us to obtain seven points of measurements of parameters of external characteristics.
Measuring the base of stichproben consisted of three volumes that are controlled by reed switches, magnetic float and three-way valves. Electronic tachometer — non-contact, inductive sensor. Temperature meter — air, registered the temperature of the cylinder heads under the candle.
To reduce friction all moving joints of the machine are equipped with ball bearings.
The work was carried out in four stages:
1) withdrawal of the original (control) characteristics of a series motor;
2) modernization;
3) characterization of the upgraded engine and test fly it on deltalat;
4) characterization of the upgraded engine without the blower and gear.
The first stage was carried out in an integrated engine stand.
Fig. 1. Components and parts production engine RMZ-640
Fig. 1. Components and parts production engine RMZ-640 “Buran”, which was newly-constructed or upgraded.
Fig. 2. Modified intake (a) and outlet (b) of the cylinder (the cylinder is deployed in the plane of the drawing).
Fig. 2. Modified intake (a) and outlet (b) of the cylinder (the cylinder is deployed in the plane of the drawing).
Fig. 3. Modified the piston (the surface of the piston is deployed in the plane of the drawing).
Fig. 3. Modified the piston (the surface of the piston is deployed in the plane of the drawing).
Fig. 4. The displacers in the crankcase: 1 — camera crank; 2 - displacers (AMG-6); 3 — M4 screw (20 pieces).
Fig. 4. The displacers in the crankcase:
1 — camera crank; 2 – displacers (AMG-6); 3 — M4 screw (20 PCs.).
Fig. 5. The displacers to the crankshaft: 1 - crankshaft; 2 - displacers (STEKLONiT epoxy binder); 3 — wells (drilling d4 to a depth of 0.5 mm, 20 PCs.).

Fig. 5. The displacers to the crankshaft:
1 – crankshaft; 2 – displacers (STEKLONiT epoxy binder); 3 — wells (drilling d4 to a depth of 0.5 mm, 20 PCs.).

Fig. 6. The cuffs unit: 1 — yoke (anodized D16T); 2 — a sealing ring, rubber (VAZ-2108); 3 to cuff (from the VAZ-2101, cropped).
Fig. 6. Block cuffs:
1 — clip (anodized D16T); 2 — a sealing ring, rubber (VAZ-2108); 3 to cuff (from the VAZ-2101, cropped).

Fig. 7. Box valve: 1 — valve plate (2 PCs); 2 — enclosure box (АЛ1); 3 — cover (АЛ1); 4 — M5 screw (8 PCs).
Fig. 7. Box of valves:
1 — valve plate (2 PCs); 2 — enclosure box (АЛ1); 3 — cover (АЛ1); 4 — M5 screw (8 PCs.).

Testing conditions: outdoor air temperature +2°C; atmospheric pressure — 746 mm Hg.St.; fuel — a mixture of gasoline AI-93 with oil MHD-14M (1:30); the carb — TO-62Ж (the diameter of the main nozzle — 1,36 mm; effective compression ratio LF = 5,6); candle — А17ДВ.
Were obtained the following results.
Screw-down feature (external load — the propeller diameter
Of 1.6 m and pitch of 0.79 m): Ne = 25,8 HP @ 5086 rpm, CE = 0,433 kg/h HP
External characteristics (external load — molinette): Ne = 27,9 5514 HP at Rev/min, CE = 0,416 kg/h HP head Temperature t°C = 212°C.
The second stage is actually upgrading. The revision was subjected; Carter (in the corners of the crank camera displacers), cylinder head (bearing surface of head undercut to
Of 1.8 mm to increase the effective compression ratio, EF increased to 7.2, the cylinders (bored intake and exhaust ports), the crankshaft (in the hollows of the cheeks installed displacers), the cuffs of the crankshaft bearing journal (cropped to 1 mm). Dispersed also the diffuser of the carburettor to the diameter of 33.6 mm, an increased diameter of the main nozzle to 2.12 mm, reduced height of the dispenser by 0.76 mm.
Valve timing (intake and exhaust) is increased. In each cylinder is made of two additional bypass channel with phases equal to the phases of the main channels (cylinder not vypressovyvaetsya).
Made from scratch; pistons, valve box, box cover, back plate valves (plate, saddles and guides), magazines cuffs.
Pistons forged from alloy АК12Д. They have two inlet ports, which reduced the temperature of the upper rings and piston heads and removed their burnout.
Unlike serial, the skirt of the new piston has bochkoobraznoj and ellipse in accordance with the temperature gradient. The geometry of the skirts ever experimentally. Since this process is quite complicated, then you can leave and regular pistons, refining them according to the attached drawings.
The body and cover of the box back of the plate valves cast АЛ1. However, it is possible to use any other foundry heat-treatable aluminum alloy.
Valve seat inserts are manufactured by pressing from ORGANICA (or Kevlar, an SVM — ultra-high-strength material) in the epoxy binder, heated to 80-85°C in the polymerization process. The sizes of saddles with slight modifications taken from the book V. M. Kondrashov and others (see references). The material of the plates of valves — laminate STEF-1, limiters steel.
As the valves and boring the Windows of the cylinders increase the volume of the crank chamber of the crankcase 41 cm3 (which reduces the pressure of the purge and, as consequence, to decrease the maximum engine power), in the hollows of the cheeks of the crankshaft and in the corners of the crank camera to the so-called displacers harmful volume. On the crankshaft they are made of glass yarns on epoxy binders (for better grip winding cheeks a drill with a diameter of 4 mm they outline the wells with a depth of 0.5 mm). The Carter plungers are aluminum half-ring of triangular cross-section, attached with M4 screws.
The amount of volume displaced in the chamber along with the volume displaced by the cuff clip is 79 cm3, which more than compensates the increase from the placement of the valves and the bore of the Windows, which ultimately improves the purging.
However, the increase in pressure in the crankcase led to the fact that regular cuffs began to be extruded from cartridges. It showed up at the first engine start-up. Had to make new clips and to build in them cuffs from the axle of the car VAZ-2101, trimmed to 1 mm and facing each other face. To seal the clips used rubber rings from the shaft of the plug from the motor vehicle VAZ-2108.
Fig. 8. Plate valve: 1 — valve seat (organically Kevlar); 2 — M3 bolt (4 PCs); 3 limiter (steel, 2pcs); 4, the damper plate (laminate STEF-1, 2).
Fig. 8. Plate valve:
1 — saddle valve (organically Kevlar); 2 — M3 bolt (4 PCs); 3 limiter (steel, 2pcs); 4, the damper plate (laminate STEF-1, 2).

Before mounting the cuff holder was heated up to 200-250°C. Then, in the cavity of the cuff to fill the grease tsiatim-201 with disulfiram molybdenum, after which the cage is mounted on the crankshaft. Their shoulder tucked into the recess of the crankcase, and the regular thrust washer removed.
In addition to these works, a conventional two-stroke internal combustion engine for the procedure for improving internal surfaces, that is, the cleanup casting in channels and Windows and fit the lines of the pairing of the crankcase and cylinders. Read more about it in the book for THEM.Grigorieva (see references).
The third stage. During the re-test was measured the parameters of external, helical, flow characteristics and the maximum temperature of the cylinder head under the spark plug. The temperature and composition of exhaust gas has not indesirables. Power was given to normal conditions. The ignition system was not changed and was not regulated.
Test conditions: outside temperature — 8°C; atmospheric pressure — 748 mm Hg.St.; fuel and the external load are the same as before the upgrade; the diffuser of the carburettor dispersed to a diameter of 33.6 mm; main jet — diameter of 2.12 mm; LF = 7,2.
The results of the tests of the upgraded engine.
Screw feature: Ne = = 31,7 HP at 5316/min, CE = 0,321 kg/h HP; head temperature t°Cmax = 204°C; capacity increase of 22.8 per cent, efficiency is 25.8%.
Exterior feature: Ne = the 38.2 BHP at 5778 rpm, CE = 0,332 kg/h HP head Temperature — t°Cmax = 208°C; the capacity gain is 36.9 percent efficiency — 20.25%.
And finally, the fourth stage. In the configuration without a gearbox, blower motor spun up to 6840 rpm, the recorded capacity of 19.6 HP, CE = 42,2 HP at 5978 rpm, CE = 0,338 kg/h HP
Under the specifications of the upgraded motor was designed and manufactured a new air screw with the profile of Wortman PX-63-137 with a diameter of 1.6 m and 0.8 m step for flight speed of 72 km/h With it on a mooring was obtained 152 kg deadlift To pull this off on production engine with the standard screw has reached 112 kg, after the upgrade — 135 kg.
Climb double ultralights with the serial engine and the standard screw was 1 m/s After the upgrade, with the same screw is 2.5—2.8 m/s; and with the newly made — 3-3,2 m/s, while fuel consumption did not exceed 9 l.
The temperature of the head of hot cylinder upgraded engine when operating in the mode of takeoff and climb when the outside temperature is +28°C did not exceed 195°C.
Outcome: after completing these stages of upgrading the engine became more smooth and soft, much easier to run. Has improved almost all of its major characteristics: power, efficiency, continuity and, most importantly, reliability. At the end of September 1999, the engine operated in flights to deltaluca 32 hours without comment.
1. Kondrashov V. M., Grigoriev Yu. S., Tupov V. V., Sillat P. P.,Abramov V. I.,Strokin A. N. Two-stroke carburetor internal combustion engines. — M., Engineering, 1990.
2. Grigoriev I. M. Motorcycle without secrets. Moscow: DOSAAF, 1973.

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