Monday, 14 March 2022

T-34's Heart on Trial

The engine is the most complicated and most important component of any tracked fighting vehicle. It might even take more time to develop the engine than the rest of the tank put together. Even today, not all tank building nations have the ability to produce their own engines, and a successful design can define the development of tanks for years to come. The V-2 diesel engine put into production in 1939 was one such design. This article will tell the story of the trials that paved its way to life.

Several BD-2-1 engines (the future V-2) were tested on the Voroshilovets tractor, two PK-1 boats, and two BT-5 tanks by the end of 1934. These early successes were followed by a length refining period that ended up taking longer than the initial design of the prototype. Even though the design was still raw, construction of a factory to produce 10,000 engines per year began, and designers of the engine were richly rewarded.

The first building of People's Commissariat of Medium Machinebuilding factory #75 in Kharkov.

Construction began before the technical project and cost calculations were completed, despite protests of some People's Commissariat employees who considered it unwise to issue funds before a design was approved for mass production. The equipment was also tremendously expensive, especially as some of it had to be imported. 

September 15th, 1937, was established as the final deadline by which the state trials had to be complete. It was later moved to the start of 1938, but that deadline was not met either. The trials that would decide if the V-2 engine would be mass produced were moved to May of 1938, but trials of the V-2 S-2 diesel that were held in April and May ended badly.

The trials commission indicated several weaknesses of the V-2 S-2 engine. There were unreliable components: weak cylinder heads and upper casing, unsatisfactory heat generation, oil leaks, etc. 12 V-2 engines were built in late 1938 taking into account these corrections. These engines were built according to the mass production processes, but under close supervision of the designers.

The main report on trials of the A-8 tank (BT-7M) with V-2 E-2S engines, and A-8 with the experimental V-2 E4, and a Voroshilovets tractor with the V-2 E4S engine contains details of the final exam, after which the  legendary V-2 would set the theme of tank designs for 80 years to come. Advantages of the diesel V-2 over the gasoline M-17T were enumerated: mobility, heat, range, special obstacle trials, tree felling trials, etc.

V-2 engine.

Technical documentation for mass produced V-2 engines was composed and approved by the ABTU as a result of these trials.

Trials of the V-2 E-2S in an A-8 tank

State trials lasted between May 10th and June 3rd, 1939. The V-2 E-2S engine presented for government trials was only broken in on a test bench at the factory. Factory trials in a tank were not performed. The engine was broken in over the course of 6 hours, after which defects were corrected. There was a total of 12 defects, including cracks in the piston rings, considerable wear of the oil pump driving gear, hammering marks on the casing, etc. The V-2 E-2S engine was first installed in an A-8 tank during state trials.

The goal of the trials was to determine the reliability of the V-2 engine, the mobility of the A-8 on tracks, and conditions in which the engine could start and operate in summer conditions.

External characteristics of the V-2 (E-2S) engine and M-17T engine at the start of the trials. Power (top graph) and fuel expenditure (bottom graph) are both tracked against engine RPM (x axis). The V-2 is shown with a solid line, M-17T is shown with a dashed line.

The engine governor began to reduce the amount of fuel supplied to the engine at 1650 RPM, so to achieve 500 hp at 1800 RPM the governor had to be adjusted. The result was that fuel expenditure increased to 171-175 grams of fuel per horsepower per hour.

The V-2's external characteristics had a smoother torque curve, which increased as the RPM decreased at a rate of 5 kg*m for each 100 RPM. The adjustability factor of the V-2 E-2S was lower than that of the M-17T at 1.18 vs 1.3-1.4.

Main data of the V-2 E-2S engine:
  • Type: four stroke naturally aspirated jet atomizing diesel engine
  • Cooling system: water
  • Number of cylinders: 12
  • Cylinder diameter: 150
  • Piston travel: 180 m (186.5 mm if articulated)
  • Engine volume: 38.88 L
  • Compression ratio: 17-18
  • Fuel injection advance angle (static): 28 degrees
  • Gearbox linkage: direct, rigid
  • Direction of driveshaft rotation: clockwise
  • Maximum power without an air filter and exhaust headers: 504 hp at 1800 RPM
  • Nominal power: 450 hp at 1750 RPM
  • Continuous power: 400 hp at 1700 RPM
  • Minimum stable RPM: 500-550
  • Maximum RPM: 1900
  • Fuel expenditure at continuous power: 168 grams of fuel per horsepower per hour
  • Dry weight: 750.7 kg
  • Dimensions with exhaust headers: L=1561, W=860, H=1062 mm
  • Starter: air or electric
After correction of defects, the engine was installed on A-8 tank #985-01. This work indicated that the control over engine production and preparations for mass production were insufficient. Some parts had to be fitted by hand. There were also issues with fuel pumps.

The test program required that the A-8 tank be run over the course of 100 hours under load with an average movement speed of no less than 25 kph. The tank ran on dirt roads, off-road, in sand, on a cobblestone road, and on a paved road (on wheels). Special trials included felling trees and towing an A-7 tank. Since there were no swamps around Kharkov, that part of the trial program was cancelled.

A-8 tank #985-01 seen from above. Differences from the regular A-7 include a lack of air cleaner on the engine compartment access hatch lid and lack of additional fuel tanks on the fenders.

The V-2 E-2S engine worked for 147 hours and 40 minutes, 105 hours and 45 minutes of which were under load during trials. The tank drove for 3273 km, of which 3050 km were covered on tracks over the course of 98 hours. The tank drove for 2151 km on a dirt road, 363 km off-road, and 214 km on a cobblestone highway. The tank drove for 223 km over the course of 6 hours and 15 minutes, 149 of which were on a dirt road, 54 km on a paved road, and 20 km on a cobblestone road.

The speed achieved was as follows:

Average speed, kph

On tracks

On wheels

Movement speed



Technical speed



Operational speed



The lowered technical and operational speeds are explained by insufficiently robust road wheel tires.

The speed was limited by keeping the engine RPM below 1300-1400. This operational mode was chosen to more closely align the tank's performance with how it would be used in service and check the performance in conditions that previously caused vibrations.

The diesel engine held its RPMs well at all times during the trials. The fuel expenditure increased as the engine had to work in tougher conditions, but not a lot. The tank consumed 2.3 L more fuel per hour off-road than on a cobblestone highway.

A-8 tank driving on difficult terrain.

The tank drove on very difficult terrain where the grades ranged from 18 to 35 degrees and tilt from 8 to 26 degrees. Areas with a slope of up to 29 degrees were traversed at a tilt of 8-19 degrees going up and down a slope of 22 degrees. The tank covered 36 km over the course of 2 hours and 32 minutes in 1st and 2nd gear at 400-1800 RPM.

The V-2 diesel proved adaptable, held its RPMs well, and quickly reacted to changes in fuel supply.

Special trials

Tree felling trials were conducted as a part of the special trials. Pine trees 250 to 620 mm in diameter growing in sandy soil were used. The attempt was made in first gear without disengaging the clutch. Three attempts to knock down a 450 mm diameter pine tree failed due to tracks slipping, but on the fourth attempt it was uprooted.

The tank could knock down 400 mm, 300+200 mm, 610 mm, and 250 mm diameter trees in 1st and 2nd gear. The engine RPM dropped from 1800 to 1600 at the moment of impact. The main clutch was not disengaged.

The V-2 diesel provided the A-8 tank with sufficient torque to knock down trees. The impacts did not cause any problems for the engine. 

Obstacle course trials included climbing a 0.8 m tall and 0.7 m wide wall. Three attempts to climb the wall in first gear led to stalling, on the fourth the tracks slipped. The wall was overcome on the fifth attempt. The vehicle was dropped from the wall abruptly as a part of the trials.

In order to tilt the engine frame, the tank was driven up on the 0.8 meter tall wall with one track, the other remained on the ground. The trials were repeated with a different orientation and direction. The front of the tank hit the ground with its front and rear when negotiating the obstacle.

Negotiating the stone wall.

An artificial obstacle was made from four beams 250-300 mm in diameter held together and dug in at a depth of 2 meters. The tank hit it with a running start in first gear with the engine working at 1600 RPM. The obstacle was tilted after three hits without disengaging the clutch.

The tank scraped its floor along the obstacle, stopping with the wheels pressing against the ground and the obstacle pressing against the floor near the water pump. The engine was shut off. The floor was caved in by 30-35 mm when the tank was on top of the obstacle and rebounded to 20 mm when removed.

The engine wouldn't start again. The deformation limited the movement of the accelerator control rod. The tank started after it was pulled off the obstacle. Trials showed that tilting the hull, impacts, and deformation of the floor did not impact the function of the engine. The deformed floor only impeded starting it due to an insufficiently thought out linkage design. Trials showed that the gap between the floor and the water pump was insufficient.

The A-8 tank towed an A-7 during trials. The tank was towed up a snaking 18 degree slope 50 meters in length on dry, flaking, clay soil in second gear and across piles of construction debris, plain ground, and cobblestones in second gear. The engine power of the V-2 was not used fully in this trial.

The tank's floor strikes the artificial obstacle.

Only one unexpected stop was made during the whole trial. A small leak in the left engine block oil pipe formed after 40 hours of operation. This defect was not corrected in the field and the tank ran the rest of the day like that. The pipe was replaced at the factory. Upon inspection, it turned out that the faulty pipe was damaged during mechanical finishing.

When the engine was inspected after 40 hours of running, it turned out that the regulator casing plug was missing. A new plug was installed. Loss of power was detected after 80-90 hours of operation. Measurements of external characteristics after the trials showed that the maximum power dropped to 485 hp, i.e. by 19 hp, due to a reduction in the fuel injection advance angle by 10 degrees and defects in fuel pump operation.

The engine worked flawlessly during trials and showed that it works reliably for the duration of the warranty period. The vibration noises did not affect its function at all.

There were several cases where the accelerator control rods malfunctioned. The rods stretched, resulting in incomplete fuel supply. There were also cases of the rods jamming when driving in sand. All issues were corrected in the field by the crews. Inspection showed issues with the cooling and lubrication systems: leaks in the filler valves and damage to hoses. These defects did not force the tank to stop.

Trials showed that the A-8 tank could tow another vehicle with the same mass along a difficult route that included turns.

The A-8's 120 L right fuel tank was used to store oil. The tank's effective capacity was 80 L, as adding more than that resulted in oil spilling out of the fuel cap. This was listed as a design defect.

The valve in the cap also didn't allow expanding air to exit, which resulted in the tank bulging, pushing out the side, and clipping the track. These defects were judged to be unrelated to the engine and caused by poorly thought out installation. The fuel pump control rods had to be thought through much more thoroughly. 

The V-2 engine temperature was very stable. Water temperature remained between 69 and 85 degrees, oil temperature between 49 and 64 on entrance and 67-83 on exit. The average ambient temperature was 15.7-23 degrees. The water and oil temperatures were lower than on the A-7 when driving at high speeds and in difficult conditions since the water didn't pick up as much heat and the oil cooling was better.

It was pointed out that when the tank idled for 5-10 minutes, the air temperature dropped by 17-20 degrees.

A-8 tank driving cross-country.

The A-8 tank could drive in top gear at 1300 RPM for 24 minutes, 12 times as long as the A-7. In second gear it could drive at 1300 RPM for hours. Thanks to a good water pump and good water cooling, the A-8 maintained stable water temperature even if the system was only half full.

The V-2 met requirements expected of a tank engine in summer conditions. It was much easier to keep an eye on water and oil temperature compared to the M-17T.

Trials showed that the tank could drive and even make 90 degree turns most of the time in third gear. The engine pulled well even in very difficult conditions. It had a much larger range in speed without changing gears than the M-17T. When climbing a 30 degree slope in first gear, the V-2 went from 400 to 1300 RPM.

The V-2 allowed the driver to switch gears less often than with the M-17T, use less energy when driving the tank, had a lower chance of stalling when overloaded, and could work for longer at low RPM.

Mobility of the A-8 tank with a V-2 engine

Mobility of the tank was measured on a dry and flat graded dirt road on tracks. Each characteristic was measured three times and an average was recorded. Trials were conducted after the engine ran for 100 hours under load.

The V-2 engine reached 1950 RPM to determine top speed, the M-17T worked at 2100 RPM. The V-2 had a noticeable reduction in power due to fuel pump defects by this point.




Top speed

61.8 kph

66.3 kph

Acceleration to 1800 RPM

Times in seconds

Distance in meters

Times in seconds

Distance in meters





The top speed reached within a short distance was 4.5 kph lower on the A-8 than the A-7. However, the A-7 could only keep its top speed up for a short period of time in the summer. Thanks to better cooling, the A-8 could maintain its top speed for a long time. The throttle response of the A-8 was worse than the A-7 and consisted of 76% of time and 78% of the path travelled in third gear. The reduced performance was explained by the reduction in the V-2's engine power by the end of the trials.
Speeds reached by the A-8 (solid) and A-7 (dashed) tanks on a graded dirt road.

The fuel economy and better efficiency of diesel of the A-8 resulted in a cruising range of 540 km on a wet dirt road without external fuel tanks, 78% more than the A-7 could achieve. This meant that the A-8 was less dependent on supply lines. The tank could also carry more fuel without increased chance of fire, which was an important aspect in many situations.

The smoke generated by the tank when driving on even terrain was negligible. There was more smoke when the amount of fuel supplied increased sharply, such as when going up a slope or driving on difficult terrain. In summer conditions the smoke did not reveal the tank, and at long range the boundary between the smoke and dust kicked up during movement could not be seen.

The tank put out a lot more smoke when going up a slope as soon as the engine RPM dropped. The amount of smoke dropped after the tank drove in a straight line for some time and the amount of fuel supplied once more matched the RPM at which the engine was operating.

When driving on a wet dirt road with no dust, the tank left a dark smoke trail 100 meters long.

The exhaust pipes did not glow at night even if the engine was heavily loaded. Sparks were occasionally observed that flew out of the exhausts and faded 1-2 meters away. The amount of smoke increased as the engine worked for longer. During one run the amount of smoke increased after three hours of operation. The cause was lowered air intake due to fouling of the air filter.

Overall, the V-2 put out more smoke than the M-17T, but the difference was mostly noticeable when the tank was going up a hill or in difficult terrain conditions when driving during the day and on wet roads. When driving on dusty roads, the smoke mixed with the dust and made it difficult to determine the type of tank, since there was more dust than smoke.

The engine put out more smoke when driving in difficult conditions, same as when driving up a slope.

Toxicity of the smoke was determined by evaluating the health of the tank's crew and the crew of the tank following it. No signs of poisoning were noticed after staying in the tank for prolonged periods of time. No signs of CO poisoning were detected in the crew that followed the tank for a long time at a short distance.

The engine was started with two electric starters powered by batteries. The diesel engine could start if the tank was horizontal or at an angle of up to 25 degrees. The air starter required a high pressure compressor and only permitted a limited number of starts. It was also unreliable and inconvenient to use. The V-2 engine was easy to start in the summer.

The following preventative maintenance was performed:
  • Daily inspection and washing of the air filter.
  • The oil was changed after 50 hours of operation.
  • Dust was wiped from the engine after 40 hours of operation.
The V-2 engine turned out to be a lot simpler to service than the M-17T. No work was needed except replacement of the oil and air filters. When repairs were conducted after the trials, it turned out that it was easy to access the engine and transmission.

The V-2 made more noise than the M-17T. Sharp noises that affected the crew more harshly were observed at medium RPM (1200-1400). If the revolutions sped up or decreased, the noise went away. The use of tank helmet intercoms allowed the crew to work the same way in the A-8 as they would in the A-7.

A number of peculiarities were found during the trials. It was not possible to drive on wheels on a paved road, as the rubber would start to melt after 30 km of driving and this led to destruction of the tire. Driving on a cobblestone road resulted in the cobblestones sinking and individual stones being torn out as the tank turned. The A-8's wheeled drive could only be used in rare scenarios depending on the terrain and weather, as well as in emergencies.

Broken tooth of the left cylinder block conical gear.

The engine was removed from the tank in working order after trials were finished. The external characteristics were once again measured. The power dropped from 504 to 485 hp. The torque dropped from 230 to 215 kg*m. The engine smoked heavily as the characteristics were measured.

The main reasons for loss in power and increased smoke was a 10 degree loss in the fuel injection advance angle, cracks in two fuel pump liners, and one broken plunger. The 1st and 4th cylinder on the right side did not engage at low throttle.

Many defects were discovered when the engine was disassembled. These included a broken spring of the fuel pump plunger, broken gear tooth on the incline shaft, and gas penetration. Nevertheless, the engine continued to function and its condition was evaluated as satisfactory.

Traces of gas penetration between the head and liner in all cylinders on the right side.

The main components (upper and lower casing, crank shaft, crankshaft bearing liners, main and articulated pistons, distribution shafts, etc) were still functional and could remain in service.

The A-8 tank with the V-2 E-2S engine received the grade of "good" as a result of these trials. The engine worked for 147 hours and 40 minutes in total, of those 129 and 15 minutes were under load, including 110 hours and 30 minutes installed in the tank, and 105 hours 45 minutes during the trials. The tank drove for 3273 km during government trials. The V-2 engine worked with no breakdowns. Compared to the engines assembled for the trials, the production engines were configured to put out more power at medium RPM and develop 500 hp at 1600 RPM. This improved the tank's torque.

The following advantages over the M-17T were recorded:
  • Lower running temperatures, even after loss of considerable amounts of water.
  • Ability to drive for longer with the cooling grilles closed.
  • Ability to maintain top speed in the summertime for longer.
  • More adaptable for various road conditions.
  • Greater range of speed without changing gears.
  • More stable RPM.
  • Greater cruising range using only main tanks.
  • Less CO in exhaust fumes, better concealment of the tank at night.
  • Simplicity of service, which was limited to daily cleaning of the air filter and oil replacement after 50 hours of running.
There were also drawbacks:
  • Exhaust smoke produced during operation.
  • Loud noise during operation, which fatigues the crew.
Trials of the V-2 E4 engine on the A-8

An experimental V-2 E4 engine was also tested alongside the production ES engine. Before state trials this engine was tested by the factory in an A-8 tank. The goal of the trials was to test the E4 variant on the A-8 tank, evaluate its performance and service parameters when running on tracks, and check the temperature during operation in the summer.

The main characteristics of the E4 variant were largely the same as those of the V-2 E-2S. Both the E4 and E-2S were assembled with manually fitted parts. Inspection and high precision measurements showed numerous defects that were then corrected. This indicated that the factory continued to adjust the engine after the 6 hour QA trials, which suggested that factory management does not diligently discover defects in a timely manner.

A-8 tank #457-62.

External characteristics were measured before the engine was installed. Heightened fuel expenditure was recorded in all modes of operation, 175-190 g/hp/hour instead of 170. The fuel system was checked and a large variance in fuel supply was found, up to 15%. The regulating weights did not make contact with the plates of the engine governor at the same time.

Later, it turned out that the fault was with improper mounting of the governor, which resulted to it cutting off the fuel supply at 1700 RPM instead of 1800 as well as unstable operation at 1700-1800 RPM. The defects were corrected, and the characteristics were measured a second time. The engine consumed 91.6 kg of fuel per hour (181 g/hp/hour) and reached a maximum power of 506 hp. The E4 engine was installed on tank #457-62 which already ran for a long time: 8559 km on tracks and 18 km on wheels. The engine was later moved to a less worn out tank.

External characteristics.

Trials of the V-2 E4 showed the same advantages and drawbacks as exhibited by the A-8 tank with the V-2 E-2S engine. 

The experimental V-2 E4 had four breakdowns during the trials. At 70 hours and 49 minutes of operation it turned out that the fuel pump shaft is not spinning. The engine was removed from the tank. The upper splined end of the vertical shaft broke after the lower retaining nut came off as a result of its lock breaking. The lock broke because it was made from brittle steel.

Tank #457-62 from the left and right.

After 77 hours and 40 minutes of operation under load, the tank's oil pressure dropped sharply. The oil pump shaft was twisted up. The engine did not have to be removed this time. The driving shaft showed signs of impacts and thorough inspection showed that there were cracks. 

Broken vertical shaft.

Oil pressure dropped again after 86 hours and 50 minutes of operation. The engine was shut off within 30 seconds. It turned out that the oil pump was not rotating. The engine was removed from the tank. Opening the lower casing showed that the intermediate gear teeth were broken. Remaining teeth were heavily worn. The pressure and scavenging stages of the oil pump both had damage from metal particles. The first stages of the filter also had a large number of metallic particles and dirt. The cause of the breakdown was insufficient toughness of the intermediate gear which was already worn at the time the previous defect occurred, but this was not noticed.

The fourth breakdown occurred after 92 hours and 18 minutes of trials after the engine worked under load for a total of 150 hours. An oil leak between the 3rd and 4th cylinder on the left side was spotted. The 4th anchoring pin on the exhaust side tore along the upper threads. This happened due to uneven tightening due to the pin not being perpendicular to the surfaces it attached to.

Twisting of the oil pump driving shaft.

The severity of the defects with the E4 engine can be judged by the fact that it was removed from the tank twice and twice installed on a test bench for breaking in: once after the vertical shaft broke and once after the oil pump drive was replaced. Other components and assemblies did not show any defects.

The issues with the E4 engine showed that individual components of the engine were not yet polished.

The state trials consisted of 100 hours and 20 minutes of operation, over which time the engine covered 3250 km. The operation of the E4 engine in an A-8 tank was judged to be unsatisfactory by the state commission, although it was stated that the components that broke could be quickly refined.

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