JaG-7

ЯАЗ
	Drawing of a JaG-7 (2017)
JaG-7
Manufacturer:	Ярославский автомобильный завод
Sales designation:	ЯГ-7
Production period:	1938-1939
Previous model:	JaG-6
Successor:	JaAZ-200
	Technical specifications
Designs:	Cot
Engines:	Gasoline engine
Power:	62.5 kW
Payload:	5 t
Perm. Total weight:	10.3 t

The JaG-7 ( Russian ЯГ-7 ) was a two-axle truck made by the Soviet manufacturer Jaroslawski Avtomobilny Sawod (short JaAZ). The prototype, which no longer exists today, was built in 1939 and was to be produced in series from 1942, which was prevented by the Second World War . Although it never went into production, it is an important link between pre-war and post-war production in the history of Soviet truck construction.

A test vehicle with a tipping bridge was also built under the name JaS-4 (Russian ЯС-4) . The JaG-7A was a single omnibus with 32 seats that used parts of the JaG-7.

Vehicle history

The same vehicle as a black and white sketch (2017)

initial situation

Heavy trucks had been built in Yaroslavsky Avtomobilny Sawod since around 1925. However, this brought various problems for the young automobile industry of the Soviet Union. While smaller trucks such as the GAZ-AA or the ZIS-5 were manufactured in large numbers from around 1933, heavier trucks could not be produced in large quantities. A number of factors were responsible, including a lack of expertise, poor roads, political planning and a lack of foreign exchange. The production figures in Yaroslavl remained low compared to other plants of the time.

In addition, the Yaroslavl plant had a decisive disadvantage compared to other automobile plants. Not all components for the trucks were manufactured in-house. Before the war, there was no engine production at the site. Since no sufficiently powerful truck engines were built elsewhere in the USSR either, they could not be easily obtained from other companies. Not only the very early models like the Ja-3 had to do with this problem , but later vehicles like the JaG-6 or the JaG-10 also remained dependent on imported engines or were underpowered.

JaAZ also built trucks until 1942, which largely went back to the technical standard of around 1920. To remedy this, a more modern design was created with the JaG-7 in the late 1930s.

Construction of the prototype

At the end of 1938, the designers at JaAZ gave up various attempts to obtain a more powerful engine from domestic production. Previously, unsuccessful attempts had been made to set up a cooperation with the Moscow Sawod imeni Stalina (ZIS), and efforts to acquire a diesel engine from an engine plant in Ufa also failed. Instead, the six-cylinder gasoline engine from the ZIS-16 bus was used for the project . Thanks to new light alloy cylinder heads and a few other improvements, this produced 12 hp more than its predecessor from the ZIS-5 truck . Nevertheless, the 85 HP turned out to be insufficient for use in the JaG-7, which weighed 10.3 tons when fully loaded and thus 4.2 tons more than the ZIS-5. The torque was too low in connection with the gearbox used, which is why the vehicle construction institute NATI specially designed a reduction gear. This solved the torque problem, but higher speeds than 52 km / h were not possible due to the lack of power. NATI was developing a diesel engine with an output of 110 to 130 hp, but the MD-23 should have been manufactured later in the engine plant in Ufa. However, this plan was never realized, and from 1939 the plant built parts for the aviation industry.

In the course of the trials, various engines were tried out on the vehicle, including the NATI MD-23 diesel engine. This was probably only used in one of a total of two prototypes, which from then on was also called the JaG-8 .

Other parts were supplied from other automobile factories. For the clutch, a two-disc dry clutch from ZIS was used, many standard parts came either from ZIS or from the Gorkowski Awtomobilny Sawod (GAZ). Only the four-speed manual transmission was new and was installed almost unchanged in the successor JaAZ-200 after the war . The use of non-ferrous metals on the vehicle has been minimized in order to save raw materials.

The body was completely rebuilt. In the literature you can find information that it was inspired by a White , other sources cite GMC or General Motors trucks as models. In fact, the prototype is visually very similar to heavy models of the GMC T-series of the 1930s.

In addition to the JaG-7 as a flatbed truck, the JaS-4 was built on the same chassis. This model also remained a prototype. It was a dump truck with a payload of four and a half tons. There was also a prototype of a bus under the identification JaG-7A, which was assembled from parts of the JaG-6 and the JaG-7. It looked like the ZIS-16 , but with 32 seats it was significantly larger. There were also plans to mass-produce a vehicle with a box body.

Further development and whereabouts

The Second World War brought fundamental upheavals in the Soviet truck industry. On the one hand, many projects and developments had to be temporarily stopped. On the other hand, the Lend Lease Act brought large quantities of reliable US vehicles to the Soviet Union. With them came new engines and other technical innovations. During the war, Detroit Diesel engines were assembled in Yaroslavl and later manufactured in-house. The in-line four- and six-cylinder two-stroke engines were to shape the Soviet diesel engine industry in the coming decades and were installed, for example, as the JaAZ-M204 and JaAZ-M206 in the later JaAZ-200. In 1959, truck production in Yaroslavl was even completely abandoned in favor of engine production.

There are reports that the JaG-7 was also fitted with a Detroit Diesel 6-71 (six-cylinder) during wartime. This model was named JaG-9 .

As early as 1941, a new truck prototype was built under the designation Ja-14 or OP-200 for a payload of seven tons. Its completion took place in 1944 and resulted in series production of the JaAZ-200 , later called MAZ-200 , in 1947 . Tens of thousands of these trucks were built until 1965. Both optically and technically, many elements were adopted from the JaG-7, which was groundbreaking for the design.

Today no JaG-7 has survived. The JaG-7A bus and the JaS-4 tipper are also no longer available. The vehicles were very likely shown to the public only once, at a parade in 1939 where various developments in the Soviet automotive industry were presented. A press photographer filmed the event, which means that a few pictures of the JaG-7 and JaS-4 have been preserved to this day.