BestBear Soviet 2WD sidecars
Driven sidecar motorcycles of the Soviet-Russian Armed Forces

The flathead (side-valve) engines

The engines usually mounted in our machines are of the flathead type, dating back to the original German BMW R71 design of the late 1930’s. Initially these were built as a license - part of the Molotov-Ribbentrob pact - under the model name M-72 (Mototsikletnyi 72) since 1940 in Moscow and Leningrad. After the German invasion production was relocated in Charkow, Gorky (GAZ) and finally, safely out of reach for German bomb-attacks, in Irbit - now the Ural factory. During war time production figures reached to around 15.000 units, under almost unworkable conditions at the start. The sidecar bodies were made by GAZ at the Gorky plant until the late 1940’s. From 1954 onwards the heavy M-72 sidecar combination became available for private ownership. Production of the M-72 by IMZ in Irbit ended in 1961, when it was replaced by the 650 cc o.h.v. M-61 model, introduced in 1959.

The Gorky based production facilities were relocated from the automobile factory GAZ to the Ukraïnian capital Kiev by 1950, thus creating the KMZ factory which became the sole supplier of the Soviet Army around 1955. M-72’s produced from 1951 by KMZ (the Dnepr factory) were almost identical to those made in Irbit, but in 1959 the model was improved with a swing-arm rear suspension, new front forks and mudguards as well as some minor alterations to the engine. The new model name was K750, produced for both the army and the civilian market. Late 1963 the K750 MW was introduced; with its reverse gear, permanent sidecar drive and differential lock this model was exclusively built for the armed forces, under stringent military quality control.

The Dnepr K750MW, a Dnepr K750 with differential device:

Both models stayed in production until 1977 when they were succeeded by the Dnepr MT12, a slightly modernised version built for the army, export and home market as well. In 1984 the production of the 750 cc flathead engines came to an end when the MT12 was taken out of production.
Over the years this flathead engine has proved to be a very sturdy and big-hearted one that could cope well with the hardships of the crude “road” and climate conditions of either Siberia or some foreign battlefield. The sidecar body is an almost direct copy of the Steib military type, used by the German forces during World War II.
The Soviet style production methods differed from those in the West: raw materials went into the immense plant and out came the finished product - not a single process was contracted out. Everything - from design, foundry, rolling and forging to final assembly - took place in the enormous factory. Only tyres, carburettors, electrical components and bearings were supplied by other (state owned) factories.

From 1958 the M72, as a derivate called Chang Yiang, has also been produced in China until 2007(!) at several factories in very large numbers, mainly for the army and other state-authorized use.
With an uninterrupted production life of almost 70 years the R71/M-72 is probably the longest produced motor vehicle in history, a convincing proof of quality of the basic 750 flathead engine of German design.

Although the entire production made in Kiev for the Soviet Army was of fairly good quality, we found some typical material flaws to iron out as well as a couple of parts for which there are far better alternatives available in West European quality.
Our upgrades include amongst others a better oilpump and recalibration of the oil distribution, better air filtration, German made piston rings, better exhaust valves and reworking of the inlet and exhaust ports, static counter-balancing of pistons and small-ends within less than 1 gramm tolerance and better (asbestos-free) clutchplates. Ignition coil, bearings and oilseals are also replaced by West European quality parts.

With these modifications BestBear upgraded engines are very reliable and smoothly running, also due to the fact that every single part is checked and if only doubtful replaced before we put the engine together again in a well equiped non-production workshop: one man builds one engine at the time, not hastened by production targets. Quality of workmanship is what counts. Quite the opposite of former Eastern-Block production philosophy you might say…..


The over-head-valve (OHV) engines

If you prefer it is also possible to equip a driven sidecar combination with the KMZ 650 cc over-head-valve engine, a development dating from the late 1960’s and also widely used by the Soviet Armed Forces.
Advantages of these engines are less weight, better fuel economy, more power, less heating and 12 volt electrics. Our upgrades however are limited to better pistons, rings and pins, counter-balancing, bearings, camshaft, valve springs, oilseals, and clutchplates.
Developing about 34 bhp at 5400 rpm these OHV engines are higher revving and will give more cruising speed on a surfaced road. However they certainly lack the rugged laid-back charm of the 30 years older 750 cc side-valve engine design with its pre-war character and manual advance-retard mechanism.


The Soviet Army machines

Due to the fact that these machines are at least 25 and sometimes over 50 years old, we can not deliver them from the shelf. Especially the versions built for the Soviet Army are in high demand nowadays and not so easy to come by. This is because their much better quality is incomparable with the civilian home-market inferior products that have flooded Europe in the years after the Cold War came to an end.

Sometimes more or less major differences between vehicles built during the same period can be found. The Soviet Army didn’t dispose worn out or written off machines to the civilian market but these were cannibalised to keep the still serviceable rest going, what remained was left to rust. In addition assembly lines behind the Iron Curtain differed from those in the Western World. When parts or components were modified the old stock was used up first before the modified ones came into the assembly process. New parts had to be fully interchancheable with the old ones, no records were kept, imposed production targets prevailed.

Dnepr vs Ural: what is the difference?

Besides a 2000 miles distance between the two factories there are some important differences between those two Soviet marques, both historically and technically.


The Dnepr factory was set up in Kiev as KMZ from 1950, equipped with the M72 production machines coming from GAZ in Gorky, to where these were evacuated from the Leningrad Red Octobre works in 1941. As the years went by more and more Kiev developed model alterations to the original design were adopted and in 1959 the K750 was a redesigned model of its own, exclusively built by KMZ at Kiev.

By that time KMZ was the sole supplier of sidecar outfits for the Soviet Armed Forces. Still relying on the 750 cc flathead engine, dating back to 1938, it was not before 1968 that a 650 cc o.h.v. engine of totally new design was introduced. The 750 cc flathead engine was taken out of production as late as 1984, evolved to the ‘modernised’ MT12 model.

A few years after the collapse of the Soviet Union in 1991 the Dnepr factory went into bankruptcy: the military orders were something of a glorious past while stringent western vehicle legislation standards could not be met for export anymore. But worst of all was the illegal stripping of the factory due to the corrupted new management. Most of the production machines were sold as scrap metal. What remains of the once proud Dnepr factory nowadays is a gigantic complex of empty buildings and ruins… even the archives have gone lost in the economical anarchy.


Ural on the contrary managed to survive these turbulent times, mainly through production orders for military sidecars from countries like Iraq and Egypt, very creative systems of barter and less economical crime and corruption in Russia than in Ukraine those days.

This motorcycle factory was founded in 1941 in Irbit as IMZ, with the production machinery from the evacuated Moscow based MMZ factory, where the M-72 - based on the 1938 BMW R71 - was built. Developing their machines gradually, Ural became the main supplier for the civil market in the Soviet Union and related areas.
Nowadays a whole range of new and retro Urals are, at a low scale export-production, built to almost Western quality standards.

Although the currently built Ural Ranger type has a driven sidecar it still differs a lot from our Dnepr with driven sidecar. The Ural does not have a differential between the rear wheel and sidecar wheel so you only have the choice of engaging (being a rigid axle) or disengaging the sidecar drive. Without a differential it is almost impossible to steer with any accuracy with an engaged sidecar drive on any kind of road surface. With a disengaged sidecar drive, as is meant for normal road usage, the Ural is just like any other conventional sidecar rigg.

The Dnepr permanent sidecar drive

The Dnepr however has a planetary differential unit mounted between the two driven wheels which distributes the drive power between the rear wheel and the sidecar wheel, so the Dnepr sidecar drive is permanent and also useable on surfaced roads.

Most military versions (the K750 MW versions) also have a locking device to block the differential under difficult terrain conditions. When one of the wheels is slipping the differential guides the traction to the slipping wheel, causing a shortage of traction on the other wheel, so it will stop turning. When the differential is blocked and acts like a rigid axle both wheels keep their traction. In this situation (difficult terrain condition) the rigid drive of the Dnepr and the Ural with engaged sidecar drive would be of temporary benefit, only to be used when necessary.

The advantages of the permanent Dnepr sidecar drive are, besides less tyre wear, a more stable and predictable ride on the road while off-road and in rough terrain steering is a lot more precise.