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Improving the reliability of the Buran snowmobile. Personal transport

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The design of the transmission of the snowmobile "Buran" has a centrifugal accelerator-variator. With sufficiently intensive use of the snowmobile, this assembly wears out within two seasons. First of all, the movable cone of the variator and the weight cams fail. The reason for such a rapid wear of these parts is quite simple: the cams rest against the depressions of the movable cone, while squeezing out deep dents. When starting the snowmobile, when the engine starts to rev up, the cams cannot smoothly exit these depressions, there is a sharp jerk of the variator belt, which leads, among other things, to rapid wear of the belt. In short, almost every season you have to change the movable cone, centrifugal accelerator and belt.

I managed to eliminate all these shortcomings only after the manufacture of a centrifugal accelerator of my own design, shown in the drawing. The blank for the cross, rollers, bushings and fingers are turned on a lathe. Cheeks can be cut from 4 mm sheet steel with a simple hacksaw, and then filed and drilled. Bushings, rollers and crosspiece must be hardened. From the old, factory accelerator, I used only a protective cover.

Centrifugal accelerator (click to enlarge): 1 - guide; 2 - washer; 3 - cheek; 4 - roller; 5 - bushing; 6 - cross; 7 - finger

The proposed alteration increases the life of the variator cone and reduces belt slippage, thereby improving traction and, consequently, increasing speed. It became possible to use the belt without replacement up to a run of 200 km.

Author: B.Pavlov

We have a battered Buran snowmobile in our home garage. I will not express my attitude towards him as a whole, since the opinions of the owners on this matter differ. However, the work of his heart - the motor has always caused not only anxiety, but also from year to year required "surgical" intervention. Every summer, preparing these "sledges" for the winter season, something was changed in the engine due to wear: either rings, or liners, or pistons.

As far as I know, these problems that arise during the operation of the RMZ-600 engine do not allow other owners of snowstorms to sleep peacefully, and the engine itself has been exciting the minds of domestic Kulibins for several decades now, trying to bring the design "to mind". We went the other way, deciding to replace the standard power unit with another, suitable one.

The idea of ​​installing the engine from the MP-80 motor pump on the Buran snowmobile belongs to my son Vladimir, since he mainly operates and repairs it. The son also selected the necessary spare parts for the new motor, since at the time the idea appeared, only cylinders and a crankcase were available. He also carried out mainly the alteration, and I only helped him when he did not have enough time or skills in the manufacture of individual complex parts.

About the engine from the motor pump MP-80. This is a two-cylinder, two-stroke engine with a working volume of about 700 cm3 (349 cm3 in each cylinder) and a power of 28 hp. liquid cooling (heat from the cylinders was taken by the pumped water flow). The maximum number of revolutions is 4800 per minute. Its crankshaft is four-bearing, placed in powerful roller bearings. The lubrication system is well thought out. The lower parts of the connecting rods are mounted on the main journals, also in roller bearings. Moreover, the rollers - without separators, are typed close to each other. I have already used this solution for the connecting rod bearing assembly more than once when reworking engines (for example, when pairing two Izh-Planet engines). In such a node, the impact from the connecting rod does not fall on one roller, but is distributed among several. The motor is very unpretentious and can pump water for days.

The pistons to the MP-80 engine came from the Izh-Planet motorcycle. By the way, they are five times cheaper than the Buranovsky ones, although the latter are worse in quality - they even burn out. The piston rings turned out to be tighter than expected, but eventually got used.

The MP-80 engine was designed to run on A-66 or A-72 gasoline. Now there is simply no such gasoline at gas stations. Therefore, the cylinder heads had to be "grinded" by one millimeter in order to reduce the volume of the combustion chamber and adapt them to AI-80 gasoline. The change in power was not measured, but due to such forcing, it should, of course, increase.

The engine muffler was left standard - from the MP-80, but it was improved, or rather supplemented with a home-made resonator cylinder, connected to the muffler through a flexible corrugated sleeve. At the same time, both the new engine and the additional resonator fit compactly under the standard hood.

The upgraded crankshaft of the power unit from the MP-80 motor pump, adapted for the Buran snowmobile, assembled (click to enlarge): 1 - left (along the way) axle shaft; 2 - thrust bearing 8207; 3 - roller bearing 42207; 4 - outer (solid) cheeks of connecting rods; 5 - connecting rods; 6 - roller bearings 2306; 7 - inner (cut) cheek of the connecting rod; 8 - ratchet kickstarter clutch; 9 - helical kickstarter gear; 10 - magneto coupling half; 11 - right axle shaft; 12 - coupling bolt (2 pcs.); 13 - central shaft; 14 - remote clutch; 15 - the main neck of the connecting rod (2 pcs.); 16 - full complement bearing rollers (as required, 2 sets)

Semi-axis of the crankshaft: a - right; b - left; the dash-dotted line shows the outlines of the original part - the standard axle shaft

Looking ahead, I note that the exhaust has become softer and can be compared with the exhaust of a four-stroke engine. The operation of the engine at medium speeds is not audible already at a distance of 40 m, and at idle - 7-8 m. But the main advantage turned out to be different. So, on the "Buran" exhaust gases were directed by a muffler through the body of the snowmobile down - ice always formed there, pieces of which had to be chipped off on trips. Now the exhaust gases exit from the starboard side to the side without getting on the driver and passenger at all. The old hole for the muffler in the body was closed with a welded overlay.

An important home-made additional detail is a special flange on which the generator (instead of the standard MP-80 magneto) and the Buran trigger are attached. I had to not only sharpen the flange myself on a lathe, but also cast a blank for it, since I could not find a suitable massive workpiece anywhere.

The material for the blank was the old duralumin pistons, which he pricked and melted in a ladle made from a tin can. The bucket diameter is about 220 mm and the height is almost 90 mm. I melted in the forge at the end of the shift, leaving the melt in the ladle on a fading fire all night. The next morning, he cut the ladle with the frozen metal with a grinder, tearing the walls with a “rose”, and pulled out a blank. The casting had a different structure: porous - in the upper layer and dense (about 2/3 of the height) - in the lower layers, which was used to make the flange.

Here I note that the flange sits on M8 studs and is fastened with nuts to the crankcase. When mounting the flange, you must first put it on the studs so that they protrude only slightly from the holes. Then lightly screw nuts on all the studs and tighten them evenly in turn.

Even in the flange "in place" a hole is drilled for the wires and two diametrically opposite grooves are made for the M5 screws. Grooves with loose screws allow you to turn the flange clockwise (or counterclockwise), which makes it possible to set an earlier (or later) ignition - to change the angle of the closed state of the breaker contacts.

Special flange

In addition to the cylinder heads, some other parts of the MP-80 engine were also reworked. First of all, this concerns its crankshaft, or rather its extreme parts (let's call them semi-axes conditionally: right and left, focusing along the way). To do this, the engine was dismantled: the cylinders were removed, the crankcase was "halved".

Let's start with the left axle. In the factory version for the MT-80, the designer seemed to have foreseen that his engine would be put on the Buran. And therefore, both of its bearings were left in place: both the support roller 42207 and the thrust ball 8207. It would be possible to keep the same length of the axis. But then there would be an unnecessarily long cantilever protruding part of it, which, if the variator pulley was displaced, would cause additional loads on the bearings. In addition, the driven pulley assembly would also have to be redone.

Therefore, they nevertheless decided to shorten the axle shaft, although not by much - by only 18 mm, transferring, respectively, all the transverse and longitudinal dimensions from the end of the shaft inward. When determining the length of the cantilever part of the axle shaft, they “danced” from the ends of the studs for attaching the stuffing box housing - after pressing the right pulley disk onto the axle shaft until it stops against the shoulder, it still should not reach the ends of the studs by at least 3 mm.

The axle shaft has factory centering holes-nests, so the processing of its end console part did not cause any difficulties, although it was necessary to strictly adhere to the tolerances for landing the right pulley disk and the variator idle speed bearing 205. A Buranovskaya bushing of the left extreme disk with weights of the variator pulley is screwed onto the threaded end of the axle shaft.

Now about the right axle. First of all, all parts sitting on it are removed from it. The free axle shaft is cut off under the root of the crank web. After that, on the other side of the cheek (there is a centering socket), a hole with a diameter of 28 mm is drilled, and then it is bored to a diameter of 29 - 0,05 mm.

The right axle shaft is vygachivaetsya new (its dimensions are shown in the drawing) - first with allowances of 2 mm, and then - exactly in size. To fit the cheek on the semi-axis, the cheek was heated. After that, the runout of the entire crankshaft was checked and the excess was eliminated. Further, setting the crank of the right connecting rod to the top dead center position, a keyway for the generator rotor was milled on the axle shaft.

The engine cooling system in the MT-80 motor pump was quite simple - the cylinders were cooled by the flow of pumped water. Therefore, for use on a snowmobile, the cooling system had to be redesigned. The main difficulty was that it (the system) should be compact and fit together with the engine under the standard hood. But even this problem was solved even with those component parts that were available or that we managed to get.

Scheme of liquid cooling of the MP-80 engine on the Buran-plus snowmobile: 1 - engine; 2-coupling (piece of rubber tube); 3-tube (regular, cut); 4-hoses (rubber tube O int. 14); 5-radiator (stove from tractor DT-75); 6 - fan (from the snowmobile "Buran"); 7-expander (gas tank from the starting engine DT-75); 8-pump (pump from a VAZ-2101 car); 9-adapter (steel, circle 45); 10-clamp (9 pcs.)

The most voluminous part (or assembly) is the radiator. In its capacity, a heater (stove) from the DT-75 tractor was adapted with virtually no alterations. And the gas tank of the starting engine of the same tractor served as an expander. Only in the cooling system is it installed "on the butt" (vertically). Since the radiator is located under the hood, and even sideways to the direction of movement (and, consequently, to the oncoming air flow), it was also equipped with a fan, which was placed between the radiator and the right cylinder, attaching the case to the crankcase. The rotation of the fan together with the pump is carried out from the crankshaft through the pulleys of the V-belt transmission.

The pump was used from a VAZ-2101 car. It had to be modified: plug the hole in the end with a 3 mm steel plate through a rubber gasket and, having drilled a hole with a diameter of 12 mm opposite the inlet pipe, welded a branch - a pipe segment with an outer diameter of 15 mm. Since the inlet pipe is designed for a hose with a diameter of 40 mm, and all pipelines of the new system have an internal diameter of 14 mm, an adapter had to be made.

The pump is attached to the radiator fan housing using a slotted bracket (from the VAZ-2101 generator) and an angle bracket with an axis (the sleeve is welded to the pump plug) to the crankcase. The pump has the ability to rotate at a small (but sufficient to tension the drive V-belt) angle.

Cylinder heads have gaskets that had only one hole near each cylinder. I had to punch six more holes with a special punch (excluding the places where the fittings were attached) so that the liquid would not follow the path of least resistance, but flow around the entire cylinder head.

The cylinder heads are interconnected by an aluminum tube. This tube was cut, drilled to a diameter of 10 mm and connected with a piece of rubber hose, tightened with clamps. Such an alteration will prevent depressurization of the tube and cylinder head connections from vibration during engine operation.

To purge the radiator in order to effectively cool the liquid circulating in it, regardless of the speed of movement and ambient temperature, an impeller (fan) is also installed. It is from the Buran snowmobile, where it was used for forced air cooling of cylinders. The rotation of the impeller, like the pump (pump), is carried out from the crankshaft through the pulleys of the V-belt transmission. And so that the impeller does not drive air past the radiator, it is enclosed in a casing, and all the slots in the radiator itself and between it and the casing of the impeller are sealed with tinplate.

Intake manifold: 1 - cylinder pipe (from the exhaust pipe of the Izh-Planet motorcycle); 2 - carburetor pipe (from the same pipe); 3 - carburetor flange (steel sheet s6); 4 - eye for fastening the carburetor (steel sheet s3, 2 pcs.); 5 - cylinder flange (steel sheet s5)

For the MP-80 engine, they bought a new K-68 Pekar carburetor. For him, I had to make another intake manifold from the exhaust pipe of the Izh-Jupiter motorcycle.

Refinement of the sub-engine platform: 1 - spring (2 pcs.); 2 - platform (steel sheet s3); 3 - fixing the platform to the spring (M8 bolt, 6 pcs.); 4 - pillow (rubber, 4 pcs.); 5 - additional plate (steel sheet s3)

To fix the new power unit on the Buran engine platform, it had to be lengthened (an additional transverse plate was welded) by 27 mm and new grooves were made to adjust its location in order to match the plane of rotation of the variator and the gear pulley. At the same time, the edges of the springs were milled a little, but inevitably (which, in general, is not scary). So that the studs for fastening the power unit (or rather, their nuts with washers) do not warp, plates of the same thickness were welded to the platform from below in place of the cut ends of the springs.

Another change on the snowmobile was more about its appearance (so to speak, design) than construction - this is a redesign of the fairing. It was "tailored" from two, installing a second headlight on it, which gave the snowmobile a more impressive look. At the same time, the standard headlight was moved to the right (along the way), and it remained the same as the road headlight (stationary). The second one has the ability to turn in its nest and even be taken out of it if necessary and used as a searchlight.

In conclusion, I would like to note the advantages that the old Buran acquired after equipping it with an engine from the MP-80 motor pump.

Firstly, the liquid cooling of the motor provides it with a stable thermal regime with an operating temperature of about 85 ° C. Secondly, the traction characteristics of the snowmobile have increased, which allows it not only to calmly overcome steeper obstacles, but also to tow heavily loaded sleds (up to 800 kg). Thirdly, spare parts are available and cheap, which is also important.

Maybe the top speed has dropped. But the snowmobile is not designed for racing on the plains and steppes. Our terrain is rugged, and even with forests, where even 45 km / h - the speed is already prohibitive. And our "Buran-plus" can roll even faster.

Author: Vit.Pronin, Vl.Pronin

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