In the second half of the thirties, the leading Soviet automobile manufacturing enterprises began to modernize their production facilities. Taking into account the future technological capabilities, new projects of promising cars were created. Together with other enterprises, the Yaroslavl Automobile Plant was preparing for modernization. Having built new workshops and mastered modern machine tools, he had to start building several new machines - first of all, a five-ton YAG-7 truck.
It should be recalled that all existing serial trucks developed by YaAZ had a lot in common. Their design went back to the Ya-3 project, based on foreign ideas from the mid-tenths of the 20th century. As a result, such machines were not perfect and did not meet the current engineering requirements. In this regard, at the end of the thirties, the YaAZ Design Bureau began developing a fundamentally new machine suitable for full-fledged operation in the foreseeable future.
New concept
Work on a new truck project started at the very beginning of 1938. Building on the successes achieved, the designers of YaAZ began to work on a machine with a payload of 7 tons. However, it immediately became clear that the project would again face the problem of engine selection. To obtain the desired traction and running characteristics, an engine with a capacity of 110-120 hp was required, but such products were not available in our country at that time.
Since the beginning of the thirties, a family of promising diesel engines under the general name "Koju" has been developed. By 1938, NATI developed a new model of this line - the MD-23 engine with a capacity of at least 110 hp, and it was proposed to use it on a new Yaroslavl truck. However, such a motor still needed fine-tuning and was not ready for mass production. It was only possible to start assembling trucks from the MD-23 in 1939.
Not wanting to waste time, Design Bureau YaAZ made a fundamental decision to create a "universal" truck project. It was proposed to create a chassis-platform suitable for installing MD-23 and capable of carrying 7 tons of cargo. In anticipation of the finished diesel engine, it was necessary to develop a "transitional" version of such a machine with a less powerful gasoline engine and 5 tons of carrying capacity. Thus, the Yaroslavl Automobile Plant could master the production of a new five-ton truck, and then switch to the production of a seven-ton truck.
The truck with a gasoline engine and a reduced payload capacity was designated as YAG-7. The second car with a diesel engine MD-23 was named YAG-8. Indexes like these can raise certain questions. The fact is that the figure in the name of the Yaroslavl truck usually indicated its payload in tons.
Considering the future modernization of production facilities, the engineers implemented a number of new solutions in the new project. However, at the time of the construction of the prototype truck, the necessary technologies were not available. Because of this, YaAZ was forced to turn to other car factories for help. In particular, the frame elements of the new design and some other units were made at the Moscow Plant. Stalin.
New design
In terms of its architecture, the YAG-7 differed little from its predecessors, but completely new units were used in its design. So, the frame was now assembled not from channels, but from stamped parts from 7-mm steel sheet. The necessary presses were not available at YaAZ, and therefore the stampings were sent from Moscow. The strength of the frame met the requirements of the YAG-8 project.
In the front part of the YAG-7 frame, a ZIS-16 carburetor engine with a power of 82 hp was placed. The inline six-cylinder engine was equipped with an MKZ-6 carburetor and was liquid-cooled. For new trucks, an improved tubular radiator was developed, but for technological reasons, a serial cellular one was used in the project. Together with the engine, the ZIS company supplied a two-disc dry clutch. Especially for YAG-7, a new four-speed manual transmission was developed in Yaroslavl. It was similar to existing products from the ZIS, but differed in gear ratios. A propeller shaft connected to the main gear of the driving rear axle departed from the box.
In the YAG-7 transmission, a demultiplier was provided to compensate for the lack of power of the ZIS-16 engine. The unified YAG-8 truck with a diesel engine of higher power did not need such a device, but could retain other transmission units.
The main gear of the rear axle was built on new components, but its general parameters have not changed. So, cylindrical spur gears were replaced by chevron gears, and bevel spur gears gave way to bevel gears with a spiral tooth. Gear ratios were determined taking into account the characteristics of the future YG-8.
The chassis received a front steered axle with single wheels and a driving rear axle with dual wheels. The suspension was based on longitudinal leaf springs, but now they were attached to the frame and axles using rubber mounts. The pneumatic brake system with vacuum booster has been redesigned. An improved serial steering gear was used on the front axle, but the large steering wheel had to be retained.
The exterior of the experienced YAG-7 was of great interest. The cars of the new models were supposed to receive an all-metal cabin with a "fashionable" appearance. However, there were problems with her. YaAZ could not manufacture such a product and was not able to order it on the side. Therefore, during the construction of the prototype, a ready-made cab from the 1936 GMC T-series truck was used. Old identification marks were removed from the cockpit and our own ones were installed. In the future, the possibility of borrowing the cab from one of the serial domestic trucks was not ruled out.
In the finished form, the YAG-7 had a metal hood with neat contours with a vertical radiator grill and horizontal louvers in the sides. There were no top hatches this time. On the sides of the hood, fenders were installed, made at the same time with the steps under the doors. The all-metal cabin accommodated a control post and two passenger seats. A tank with a capacity of 175 liters was installed under the seats. The cockpit had a frontal glazing with a B-pillar and lifting windows in the doors.
A simple side body made of wood and metal parts was used as a loading platform. The front and rear sides were fixed, and the side ones could be reclined to the sides. In the future, the possibility of using YAG-7 and YAG-8 as a base for special equipment or a dump truck was not ruled out.
The total length of the YAG-7 truck was 6, 7 m, width - 2, 5 m, height - 2, 32 m. The base and track corresponded to the previous YAZ vehicles. Curb weight - 5, 3 tons, carrying capacity - 5 tons. The design speed on the highway reached 50-52 km / h. The promising YAG-8 car with the MD-23 diesel engine was supposed to have similar dimensions and weight, but differ in an increased carrying capacity - 7 tons.
Prototypes and developments
The development of new cars took several months, which is why the construction of two prototype chassis was only started in 1939. The assembly of the two prototypes was completed in early November, and immediately after that they went to Moscow. Two samples were to become exhibits of an exhibition dedicated to the 15th anniversary of the Soviet automotive industry. After the end of the exhibition, the cars were sent to NATI.
Two vehicles of different types were simultaneously tested. First of all, the YAG-7 itself was brought to them in the configuration of an onboard truck. The second prototype had a slightly reduced base and was a dump truck. This version of the car received its own name YAS-4.
YAS-4 was distinguished by a reinforced frame with hinges for a lifting body. The hydraulic system was responsible for lifting the body, the pump of which was driven by the propeller shaft. The car was equipped with an all-metal welded rectangular body. Bulk cargo was dropped through an opening swinging tailgate. As in the case of previous dump trucks, the installation of new equipment led to a heavier machine and a reduction in carrying capacity - up to 4500 kg.
Over the next months, the specialists of YaAZ and NATI carried out the necessary tests and confirmed the calculated characteristics of the equipment, and also identified the ways of the required revision. The design bureau of the plant began to improve the project.
On March 10, 1940, the Council of People's Commissars adopted a decree on the modernization of the Yaroslavl Automobile Plant. Until 1942, it was planned to build a number of new workshops, with the help of which the enterprise would be able to produce a wide range of new products of various kinds, including engines and transmission units. The modernized plant would be able to master the full production cycle. Until the end of the reconstruction, the YaAZ design bureau was supposed to develop new truck projects intended to be launched into series together with the YaG-7.
A sad ending
Unfortunately, after the tests in the spring of 1940, the traces of the YAG-7 and YAS-4 prototypes are lost. At the same time, there is fragmentary information about the continuation of work on the YAG-8 project. A prototype of such a machine was completed at the very end of 1941, but there is no exact data on it. In particular, it is not known if the automakers were able to equip it with the originally planned diesel engine.
However, the diesel YAG-8 no longer had any prospects. Diesel engines of the "Koju" family were planned to be produced at the Ufa Engine-Building Plant, but by this time the enterprise was transferred to the aviation industry. They did not look for a new site for the production of diesel engines. Thus, the YAG-8 was left without real prospects and, after testing, had to go for disassembly. In the future, on the basis of the YAG-8, it was supposed to develop a YAS-5 dump truck, but this project remained on paper.
The modernization of production facilities was delayed and by the beginning of the Great Patriotic War was only partially completed. However, the Red Army and the national economy have not yet risked being left without heavy trucks. The assembly of YAG-6 machines in basic and modified versions continued until 1942, when YAZ was left without ZIS engines.
While releasing YAG-6 trucks, the Yaroslavl Automobile Plant did not stop designing equipment. In 1941-42, new samples were created on the basis of the YAG-7 platform. In particular, the possibility of equipping this machine with American engines was being considered. The purchase of engines abroad, in theory, also made it possible to put an updated version of the YAG-8 diesel into the series. Moreover, YaAZ even managed to obtain a number of GMC-4-71 engines and test them on serial trucks.
However, all these works no longer made sense. At the turn of 1942 and 1943, it was decided to redesign the Yaroslavl Automobile Plant. Now he had to assemble not trucks, but tracked artillery tractors developed by NATI. In 1943, the first batch of Ya-11 tractors rolled off the assembly line. In the future, they were repeatedly modernized and built in a large series.
YaAZ returned to the topic of trucks after the war. In 1946-47, completely new models of equipment appeared, developed without the widespread use of existing ideas and solutions proposed in previous projects. In fact, a new era began in the history of the plant.
The Yaroslavl Automobile Plant has been developing and building trucks of various models since the mid-twenties. Almost all such projects were created by deep modernization of old ones, and only in the late thirties the enterprise was able to create a completely new platform. Unfortunately, circumstances developed in such a way that these cars did not reach mass production. The creation and launch of production of a fundamentally new line has shifted for several years.
