M-72 review. Part 1.
M-72 review. Part 2.

Motorworld’s newspaper № 38

Based on BMW R-71, the pre-WWII model, the Soviet heavy motorcycle model M-72 had been produced from 1941 to the mid-1950s. The design work was commenced in 1939 when the Soviet government, alarmed with Hitler’s ambitions re expanding German-controlled territory, started its rearmament program for the Red Army. Germans already had their successes in designing heavy motorcycles, so a decision was made to “adapt” a relevant German technological solution—in order to save time.

V. M. Molotov, Minister of Foreign Affairs of the USSR, arranged for a secret purchase of five BMW R-71 motorcycles in Sweden, after which Soviet designers immediately started their work. By the spring of 1941, the production of the model under the label M-72 was launched at the Moscow Motorcycle Plant (MMZ). Under cooperation agreements the ZiS, a Moscow automobile plant developed the documentation and delivered engines for the motorcycle, while the KIM (today the AZLK Automobile Plant, also in Moscow) provided gearboxes, and the GAZ, the Gorky Automobile Plant, produced the cardan shaft and the sidecar. The Moscow Bicycle Plant produced these motorcycles until 1951. The second production base was launched at a Kharkov plant, and it was getting engines from the Kiev Plant of Medical Instrumentation. In Leningrad, the Krasny Oktyabr [Red October] plant also took up the production of the M-72. After February 1942 M-72 motorcycles were being manufactured in Irbit (see Irbit Motorcycle Plant), since equipment and machinery from the MMZ, KiM, ATE-1 as well as the motor shop from the ZiS were evacuated. Main Design Bureau also was relocated from Moscow to Irbit. It was headed by Aleksandr Minovich Fyodorov, while I.I. Okunev, N.A. Kukin, V.V. Bekman were among its designers and S.I. Karzinkin and B.V. Zefirov were its test drivers.

The structural design of BMW R-71 was made having mass production in mind, and, at the same time, it had many novel technical solutions that were not used in Soviet motorcycles yet. These were, e.g., duplex frame, gear changing by foot, spring suspension of the rear wheel, telescopic front fork, cardan drive, feeding each cylinder from a separate carburetor.
The opposed allocation of the cylinders in the engine provided not only its great balance but also a low center of gravity for the motorcycle as a whole. For M-72 it was located at the height of 592 mm.

All auxiliary units of the M-72 (breaker, oil pump, generator) were driven with cogwheels; pig-iron cylinders were coated with anticorrosion, heat-resistant black japan; crankshaft rod-bearers were of the roller-track type, while main bearers were ball-type. Connecting rods were not mounted on a common neck, but each had its own.
This is why the left cylinder (as seen from the motorcycle) was staggered forward by 39.2 mm as compared to the right cylinder. With the aim of decreasing the length of the motor case and, correspondingly, its mass (75 kg with the box), a two-bearing crankshaft was designed for the M-72, just as for its prototype, the BMW R-71; its middle cheek was made relatively thin (18 mm). Overloading this engine, when the load on the crank-drive assembly was rising, resulted occasionally in the breakdown of this cheek, even though it was made of high-quality steel (ZOKhMA or ZOKhGSA types).)

On this motorcycle, bags for ammunition and spare parts were installed, as well as special brackets with a pan-and-tilt arrangement to install a machinegun (revolving bracket). The Degtyaryov machine gun was mounted via bipods on the base of the revolving bracket, which made its transportation easier and allowed firing from a rest position as well as when riding. Tubular brackets in front of and at the back of the sidecar, which provided the means for inserting the revolving bracket, made firing possible both along the direction of the driving and to the back side. The army also got in very small numbers motorcycle modifications with an 82-mm mortar launcher mounted instead of the sidecar case.

This motorcycle went through a slow cycle of modernization before the IMZ started producing an advanced model M-72N in 1956. Thus, in 1949 the plant introduced a double air filter, both mesh filter and inertial oil filter, which was more effective than the previous one, the mesh filter. After 1950 the motorcycles were completed with a new generator regulator, RR-31, instead of the initial one, RR-1. Later on, in 1952, an improved generator was introduced, G11A. Its capacity, however, was the same, both for its preceding version (G11) and its subsequent model (G414). For the whole duration of the M-72 production (including its heirs), the structure of the carburetor K-37, the size of the tires (3.75 x 19) and some other units have remained unchanged.

Over the whole production period, a total of more than 330 thousand M-72 motorcycles were manufactured.

Materials from the article «Heirs of BMW R-71» at Moto.By were used here.

Manufacturer Irbit Motorcycle Plant, Irbit (USSR)
Years of manufacture 1941 – 1956
Quantity produced, units Over 330,000
Price
Today’s value
ENGINE AND TRANSMISSION
Type twin-cylinder, horizontally-opposed
Engine capacity, cc 746
Bore and stroke, mm 78 х 78
Engine rating 22 h.p. at 4600 rpm
Sparking G11 generator
Carburetor K-37 – 2 units
Battery 3 MT-14, 6 V
Clutch Dry double plate
Transmission 4-speed
FRAME AND WHEELBASE
Frame type Duplex tubular
Front suspension Spring-mounted, with hydraulic shock absorber
Rear suspension Candle-type spring-mounted, with no shock absorber
Brakes Drum type
Wheel size 3,75 х 19
DIMENSIONS
Length, mm
2 380
Width, mm
1 590
Height, mm
1 000
Wheelbase, mm
1 400
Ground clearance, mm
   132
Seat height, mm
   790
Mass, kg
   336
Gas tank size, l
     22
Maximum speed, km/h
     85
Range, km
   314