Yes-12

ЯАЗ
Ja-12 as a memorial on the premises of the manufacturer's plant (2014)
Yes-12
Manufacturer:	Ярославский автомобильный завод
Sales designation:	Я-11, Я-12, Я-13, М-12А, М-13А
Production period:	1942-1948
Previous model:	JaSP (indirect)
Successor:	none
Technical specifications
Designs:	Cot
Engines:	Otto and diesel engines
Power:	63.3-82.4 kW
Payload:	2 t
Perm. Total weight:	7.42-8.74 t

The Ja-12 ( Russian Я-12 ) is an artillery tractor with a tracked chassis from the Soviet manufacturer Yaroslavsky Avtomobilny Sawod (short JaAZ, Russian ЯАЗ). It was produced in series for the Red Army from 1942 to 1948 , with around 2500 copies of different versions being built. Due to various design changes and a change of manufacturer, the vehicles were also referred to as Ja-11 , Ja-13 , M-12A and M-13A .

Vehicle history

Yes-11

At the beginning of the Second World War , the Red Army lacked large numbers of artillery tractors. It is true that suitable machines were built in the Stalingradski Traktorny Sawod with models such as the STS-5 Stalinez , but the factory could not deliver the required quantities. With the Battle of Stalingrad from 1942 it also had to stop production. The existing vehicles were often lost during the fighting, so that replacements were urgently needed.

Various tests followed with components from the T-40 , T-60 and T-70 tanks , with the aim of finding a suitable drive. The designers came up with the solution of installing two GAZ-M1 engines in parallel. The development work on the caterpillar tractor project "D" (Russian "Д" for "двухмоторный" - twin-engine) took place at the NATI research institute in Moscow, using earlier designs from 1940. The work had to be interrupted in the meantime due to the battle of Moscow and could not be resumed until 1942.

The first tests with the new vehicle took place in autumn 1942. They were largely successful, but difficulties persisted. The motors had to be synchronized mechanically, which often caused problems. A new cooler with a large fan reduced the available power of the engines from 50 to only 43 hp. In practice, the performance was not significantly higher than that of the six-cylinder engine of the ZIS-5 truck , which would have made a much simpler construction possible. The engines of the GAZ-M1 were also known for their lack of reliability. Pistons and connecting rod bearings wore out quickly, and the oil supply was inadequate on slopes. This often resulted in bearing damage. In order to be able to transmit the torque, the springs on the clutch had to be reinforced, which in turn meant that the required pedal pressure when clutching rose to far too high values. The manual transmission was adopted from the GAZ-AA truck , but it turned out to be not very wear-resistant and undersized. Many components were taken over from light tanks, the chassis, for example, came almost entirely from the T-60.

Despite the existing problems, the construction was handed over to the Jaroslawski Awtomobilny Sawod for production. The factory was chosen because there were enough gear cutting machines and other complex tools available there to guarantee production. In November 1942, the order was sent to Yaroslavl to start production and to adapt the vehicle as necessary to the conditions in the plant. Here the project was named Ja-11.

New problems arose in the Yaroslavl plant. For one thing, production had to be switched from civilian trucks like the JaG-6 to military equipment within three months . On the other hand, there were problems with the manufacture of the undercarriage parts and the traction of the vehicle in the field. Accordingly, the trailer load had to be reduced to 5000 kg. Various parts of the drive train also proved problematic. Since there was a lack of manganese , steel with a lower hardness had to be used, which greatly increased wear. The platform was adapted at the request of the military and, with almost five square meters, offered enough space to carry up to ten soldiers with equipment and ammunition for the gun. In addition, the tractor received a lighting system.

Due to the changed design and the fact that non-ferrous metals had to be saved and replaced by steel, the weight increased significantly compared to the prototype. Many technical difficulties persisted, but series production was to begin in mid-1943, initially with 50 units. By then, depending on the information, three or five prototypes had been built. Further tests were carried out in May and early June 1943. A total of twelve frames were built, but ultimately they could not be used. In June 1943 heavy bombing hit the Gorkowski Avtomobilny Zavod , which was supposed to deliver the engines for the Ja-11. Since other engines did not match the design, the project had to be revised.

Yes-12

Side view of the same Ja-12 (2014)

Rear view (2014)

Look under the vehicle (2014)

As early as 1941, the director of JaAZ, AA Nikanorow, had written to Stalin an application to buy US engines from Detroit Diesel . Stalin approved this application and the engines were actually delivered to Vladivostok , in Yaroslavl the order had meanwhile been forgotten due to the chaos of war. When the search for a new possible engine for the Ja-11 began in 1943, people remembered the 1500 two-stroke diesel engines of the type 4-71, which were actually still available in Vladivostok. Within a few weeks, the now named Ja-12 design was changed and adapted to the new engine. Among other things, the fuel system was changed, additional instruments installed, the cooling system revised and the electrics completely revised.

Changes have also been made to the drive train. The more powerful, slower turning diesel engine made it possible to reduce the overall gear ratio. The gearbox was rigidly attached to the frame at four points, and the loading platform was reduced in size. Now there was only room for eight soldiers. Spare parts were now attached outside, so they no longer had to be carried on the loading area. The driver's cab was also made narrower so that only two people could sit in it instead of the previous three. The more powerful engine increased the maximum speed on the road to 37 km / h and the trailer load to 8000 kg. Thus even the heavy 152 mm cannon howitzer M1937 (ML-20) could be pulled.

Tests with the Ja-12 were carried out in the fall of 1943, followed by series production. In 1944 the vehicle was successfully introduced into the army and showed satisfactory driving characteristics. The engine life was 700 hours, that of the chassis about 3000 kilometers. An average speed of 13 km / h could be achieved off-road under load and 17 km / h on the road. In operation, however, there were again defects. The suspension was designed too weak for full load and the necessary material quality could not always be maintained, which kept parts breaking. The drive wheels of the chain drive were also not always in perfect condition, which led to teeth breaking off. The repairs were made easier by the fact that many parts were identical in construction to those of the self-propelled gun SU-76M , which were produced in factories with better equipment, which also delivered better quality. Off-road, and especially on icy ground, it became apparent again that the chassis could not provide enough traction. Three of the tractors had to be used on icy slopes to move five tons of trailer load. Some of them were also much larger chain Tractors of the type Stalinez-65 coupled.

It turned out to be difficult to operate the two-stroke diesel engine at particularly low temperatures. There were attempts to let the engines run at low speed overnight, but this caused various components to become clogged. Even so, production reached a level of two to three vehicles a day, which was quite a lot for JaAZ at the time. From August 1943 to December 1946 a total of 2296 Ja-12s were manufactured, the majority of which were made in 1944 and 1945 and only 67 tugs were built in 1946. Production was then transferred to another factory in Mytishchi and continued there as the M-12A.

At the end of the war, the Red Army still had 1270 units of all variants of the Ja-12 in stock. They were used until at least 1954, after which they were segregated and scrapped. Since the procurement of spare parts proved to be difficult, self-produced engines of the type JaAZ-204 were often installed during repairs, a copy of the original Detroit diesel unit with metric dimensions. A smuggler had already gone to a museum in 1945, but it was closed in 1967. In the course of this, the vehicle was scrapped. JaAZ himself used one of the traction devices in the internal works traffic and restored it later. Today it stands as a memorial on a pedestal on the factory premises (color photos on this page).

Yes-13

Since it was foreseeable that the Detroit diesel engines would not be sufficient, JaAZ was looking for a domestic alternative at an early stage. In the autumn of 1943, the six-cylinder gasoline engine in the ZIS-5 truck had developed so far that it could normally produce 73 and a maximum of 80 hp. This made it a possible alternative for the US diesel engines. From 1944 it was also manufactured in the safe Uralsky Avtomobilny Zavod imeni Stalina in Miass , which the German bombers could not reach. Nevertheless, modifications had to be made to the vehicle, in particular the overall gear ratio was too low. It was changed, but at the same time the top speed was reduced to around 20 km / h. Under load, the tractor was still able to travel 13 km / h on the road and 9 km / h off-road. The fuel consumption rose sharply, which halved the range to around 200 kilometers.

One advantage of the gasoline engine was that it could also be started by hand with a crank due to its lower compression. The more complex start-up procedures required for diesel engines were therefore no longer necessary. The traction properties in the field improved slightly thanks to a revised chassis. However, the engines tended to overheat certain assemblies and frequently failed. That is why they were later replaced by other brands. 71 Ja-13 vehicles had been built by the end of 1943, nothing is known about any further production.

Yes-13F

Because of the known problems of the ZIS-5 engine, the search continued for alternatives. The next suitable variant appeared to be the very similar engine from the ZIS-16 bus , which was already equipped in the civil version with light metal cylinder heads and had a compression ratio of 6.1: 1. This reached the limit that gasoline with around 70 octane permitted, because its knock resistance was too low for higher compression rates. Nevertheless, further modifications were made and an engine output of 95 hp was achieved. The engine with the designation ZIS-5MF or even just ZIS-MF (MF for миасский форсированный, analogously "from Miass, performance-enhanced") was installed in some prototypes from November 1943, which were given the designation Ja-13F. The engine received a new carburetor and a revised flywheel.

The revised engine increased the torque slightly, but at the same time made the vehicle heavier. The trailer load had to be limited to five tons. The oil cooling and supply of the bearing points with oil remained a problem, which could not be completely resolved. Three of the vehicles were built in 1944 and another two in 1945. Also because the Americans later regularly delivered more Detroit Diesel engines under the lending and leasing law , series production in Yaroslavl was not started. Instead, production was moved to Plant No. 40 (Мытищинский машиностроительный завод, Mytishchinsky Maschinostroitelny Sawod , Mytishchin Mechanical Engineering Plant ), where tractors with the ZIS-MF engine were also manufactured in series.

The last surviving Ja-13F was in the above-mentioned military museum until 1967 and was then scrapped.

M-12A

At the end of 1944, production of the Ja-12 was also relocated to the mechanical engineering plant in Mytishchi. The manufacturer-specific part of the type designation changed from Yes to M, which stands for the first letter of the manufacturer. In addition, the letter A was added to the number to indicate that it is a new version of the vehicle. The relocation to the factory was deliberate, as the SU-76M self-propelled gun was already being manufactured there, from which the chain tractor took many assemblies. At the same time, various minor improvements were made. The tank was enlarged by 50 l, the clutch reinforced, the insufficient ground clearance increased and the gearbox swapped for that of the SU-76M. As a result, the top speed decreased slightly. The 4-71 Detroit diesel engine continued to serve as the drive.

As a result of the changes, the vehicle became heavier, and the maximum trailer load had to be limited to 6000 kilograms. This was mainly due to the unreliability of various drive and chassis components that were too weak for the design. The new name M-12 or M-12A could not prevail in the army, there the vehicle was continued as Ja-12. In 1946, the production of small series began in Mytishchi, in 1948 production was ended, although there were frequent interruptions in between. The last M-12A was also scrapped in 1967 in connection with the museum's dissolution. In Yaroslavl, the production of military vehicles was stopped after the war and trucks were built again.

M-13A

The production of the Ja-13F was also relocated to the mechanical engineering plant in Mytishchi and continued as the M-13A. In 1945, parallel to the diesel version, production of petrol-engined vehicles began there, and the same design changes were made to the M-12A. The power of the gasoline engine was increased to 99 hp, increasing the top speed by almost four kilometers per hour. As with the M-12A, the curb weight also increased. For this reason, a prototype with a lighter body was built in 1946, but this was not taken over into series production.

The M-13A was also built until 1948. Around the turn of the year 1946/47, some M-13A were tested by the NATI Institute, which found serious defects in the engine in particular. Manufacturing defects and poor factory settings were found, and the material quality did not meet the requirements. Nevertheless, the engines tested lasted around 500 operating hours on average.

Similar to the M-12A, the new designation could not establish itself in the military, it remained with the designation Ja-13 or Ja-13F. The tractors were used until the 1950s and then retired.

Technical data of all versions

As far as known.

Vehicle type	Yes-11	Yes-12	M-12A	Yes-13F	M-13A
(first) year of construction	1942/43	1943	1944		1945/46
engine	2 × four-cylinder, four-stroke gasoline engines	Four cylinder two-stroke diesel engine		Six-cylinder four-stroke gasoline engine
Engine type	2 × GAZ -M	GMC 4-71		ZIS -5MF
power	2 × 43 hp	112 hp		95 hp	99 hp
Range	325 km	350 km	415 km	250 km	295 km
Top speed	29.4 km / h	37.1 km / h	35 km / h	24 km / h	27.7 km / h
Seats in the cabin	3
Seats on the loading area	8 to 10	8th
length	4890 mm		4873 mm	4890 mm	4873 mm
width	2440 mm		2450 mm	2440 mm	2450 mm
height	2213 mm	2215 mm	2290 mm		2295 mm
Ground clearance	358 mm	305 mm	350 mm	310 mm	355 mm
Empty weight	5418 kg	6550 kg	6740 kg	5710 kg	5905 kg
Payload	2000 kg
Trailer load	5000 kg	8000 kg	6000 kg	5000 kg
specific ground pressure	0.456 kg / cm²	0.526 kg / cm²	0.538 kg / cm²	0.474 kg / cm²	0.486 kg / cm²

Individual evidence

1. ↑ ^{a b c d e f g h i j k l} Detailed website for the Ja-12 and its model variants. Part 1. (Russian)
2. ↑ ^{a b c d e f g h i j k} Detailed website for the Ja-12 and its model variants. Part 2. (Russian)
3. ↑ LM Shugurov: АВТОМОБИЛИ. России и СССР. First part. S 170 f.

literature

• LM Shugurov: АВТОМОБИЛИ. России и СССР. First part. Ilbi / Prostreks, Moscow 1993, ISBN 5-87483-004-9 .

Web links

Commons : Ja-12  - Collection of pictures, videos and audio files

• Manufacturer website on the history of the plant's automobile production (Russian)
• Website with basic information on Ja-12 (Russian)