Tuesday 31 December 2013

HPZ BT-7 and T-35 Woes

"Report on the condition of tank-building at the Kharkov Locomotive Plant in the first half of 1936

The "Spetsmashtrest" plan assigned the production of 510 vehicles to HPZ in the first half of 1936.

Only 425 tanks were produced in this time. ABTU accepted only 271 of these tanks. More specifically: out of the 100 tanks prepared in January, ABTU accepted 60, from 115 in February, ABTU accepted 99, out of 95 from March, 81, out of 51 in April, 25, out of 48 in May, none, out of 16 in June, 6.

The main problem is the low quality of a number of components in BT-7 tanks, reducing their combat quality. This is mainly caused by the design of the BT-7 using several components from the BT-5, which the factory transferred without consideration for the increased engine power and vehicle weight.

Data in our possession indicates that the chief of the tank design bureau at HPZ, engineer Firsov, removed himself from regulating work on this tank. All of Firsov's work was transferred to his assistant, Granberg, who had no experience in tank building, and did not make correct technical decisions in the design and construction of the BT-7.

The following defects of BT-7 tanks have been established:
  • Incorrect assembly of the gearbox, resulting in mass breakage of the gears.
  • The dust filter is inadequate. After 30-40 hours, the engine ceases working, due to dust in the cylinders and cylinder rings.
  • Installing and removing the batteries is difficult. Instead of the required 8 minutes, it takes up to 2 hours.
  • The removal of water from the radiators is inconvenient, plus it is impossible to purge all oil from the oil system.
  • There are many cases of shorts in the electrical systems, increasing the chance of fire in the tank.
  • Tracks are useful for 700-800 kilometers. According to the warranty negotiated with the RKKA, they should be functional for 2000 kilometers.
  • Additionally, after 100 km, the track is loose and hangs on the wheels, slides off, and does not allow the tank to move normally.
  • After ballistics tests of a 1935 hull and turret, it was deemed that the rivets are not bulletproof. A part of them was knocked out, the gas tank was penetrated, as were the hinges on the driver's hatch.
  • Only one defect from other factories is worthy of attention: the use of ball bearings #6217 and #6411 from the 2nd State Ball Bearing Factory in gearboxes and gear change brackets. These ball bearings, due to metal quality and poor thermal conditioning, cannot be used on tanks. All ball bearings on tanks at HPZ were replaced, but the tanks in the army still contain 2nd GPZ ball bearings.
In March of this year, when the first problems with gear change brackets happened, the tank laboratory chief  Gorbodei at HPZ ordered that the gear change bracket should be hidden, and not disassembled or analyzed. Gorbodei claimed it was the order of the deputy chief of the tank department, engineer Kulikov, and said that if the bracket is disassembled, the military representatives will know, and will cease accepting tanks.

HPZ continues to ignore our questions regarding the quality of BT-7 tanks, as mentioned in our previous report from April 19th of this year (#528).

The factory director, comrade Bondarenko, was called to Moscow in June of this year. According to NKVD information, despite these defects, another batch of BT-7s is going to be sent to the RKKA. 

As for the T-35 tanks, the factory was supposed to produce 9 in the first half of this year, and only produced 6.

The existing T-35 tanks have the following problems:
  • Rapid wearing of the engine components due to a poor dust filter.
  • The rollers on the gearbox bend and vibrate during operation.
  • The final drives leak. It is necessary to redesign the final drives.
HPZ is currently working on correcting these faults with T-35 tanks.

Acting Deputy People's Commissar of Internal Affairs of the Ukrainian SSR
Commissar of State Security, 3rd grade, S. Mazo

July 16th, 1936
RGASPI 558-2-142

You know you screwed up when the NKVD comes knocking at your door. Contrary to popular history, all of HPZ didn't immediately face execution, and action was taken to resolve the identified problems. 

"To the People's Commissar of Heavy Manufacturing, comrade G.K. Ordzhonikidze

The acceptance of BT-7 tanks with the M-17 aircraft engine and reinforced gearbox continues on July 15th, after lengthy trials with ABTU and the People's Commissariat of Defense. 

The missing BT-7 tanks in the first half of 1936 will be delivered to the NKO by November 1st.

As for the issues communicated by comrades Gai and Mazo, we consider it necessary to report the following:

On the BT-7 tank
Gearbox: in April of 1936, it was determined that the conical gears of the gearbox are destroyed before the warranty period expires when operating on tracks. When this was discovered, HPZ immediately stopped sending tanks, and tested 13 tanks on tracks. 7 tanks did not manage the warranty period, only making it 500-700 km on tracks. These trials demonstrated that the cause of these breakdowns is the increased momentum of the M-17 engine when compared to the Liberty engine.

HPZ used all possible resources to make 9 design changes to the gearbox, increasing its strength 2-2.5 times compared to the May production gearbox.

At the same time, in order to increase the warranty period, according to the professor of the Academy of Motorization comrade Stepanov, the factory decreased the momentum of the M-17 engine from 280 kg-m to 220 kg-m.

Four BT-7 tanks with reinforced gearboxes and 220 kg-m moments were tested at great length by the factory and ABTU. Trials were performed in most difficult conditions for the gearbox, exclusively on tracks (the wheel load on the gearbox is 2-3 times lighter). Even in these conditions, the two first tanks travelled 1400 km, and the second two, 2000-2500 km. These trials convinced ABTU of the combat ability of the fast convertible drive BT-7 tank with the reinforced gearbox, which is capable of providing 2000 km of service, of those 1300 on tracks, which is acceptable by standards set by ABTU for 1936.

As for the history of the BT-7's development, we report that as of January 15th, 1935, the factory and ABTU completed an experimental BT-7 tank, that had an identical gearbox to the BT-5. That tank travelled 1100 km on tracks and 1300 km on wheels. A second identical prototype was tested by ABTU on an obstacle course.

On January 29th, 1935, the factory presented ABTU with a design for a BT-5 gearbox (#08-S20) and changes to it (#08-S23). The chief of ABTU's technical department, brigade engineer comrade Lebedev, wrote on the blueprint on January 29th, 1935:
  1. The conical pair component must be altered according to blueprint #08-S23.
  2. Produce an experimental prototype of a further reinforced version of this component, according to diagram #P-11-1"
Blueprint #08-S23 contained a number of changes to the BT-5 gearbox, consisting of:
  1. An increased number of retention bolts, from 10 to 12, with an increased diameter of their location (110 mm to 135 mm).
  2. The roller clamps are reinforced, 17 mm from 13 mm.
  3. The gear clamps are reinforced, from 13 mm to 11 mm.
On February 5th, 1935 (after 8 days), Lebedev was presented with blueprint #08-S23, which he accepted.

On June 19th, 1935, as a result of an NKO report, the STO accepted this tank into service.

The subsequent series of events, as detailed above, shows that the factory and ABTU made a miscalculation in the attachment of the gearbox conical pair, which has since been corrected.

Simultaneously with the new production of the BT-7 with a new gearbox, 687 BT-7 tanks already in the army will also receive new gearboxes. According to the agreement with ABTU, the gearboxes will be replaced between August 1st and December 10th, 1936.

ABTU is counting the unreinforced BT-7 gearboxes removed from its tanks towards the BT-5 spare parts contract for 1936.

Anticipating the growing requirements of ABTU, HPZ began development of even more reinforced gearboxes, which will begin testing in the 4th quarter.

ABTU released special instructions on March 4th, 1936 on how to drive the BT-7 tank. These instructions should be read by anyone driving a tank, not just the BT-7.

On the issue of wheel bolts: the issue was resolved by replacing regular metal bolts with bolts made from #5 steel.

On the issue of tracks: as on all tanks, BT-7 tracks break in during the first 100-200 km, and somewhat lengthen, requiring adjustment. An idler adjustment mechanism exists on the tank for this purpose. Latest factory and army trials show that, if track pins are replaced, tracks last from 1161 km to 1564 km.

On dust filters: currently, new dust filters are being used, several times better than the old ones. After 2500 km of trials with the new filters, no engine trouble is seen. These new filters are installed in all vehicles produced by the factory.

On removing batteries: the batteries must be removed very rarely, in exceptional conditions. Due to the increased size of the ammunition rack on the BT-7 and larger size of the M-17 engine, the removal of batteries is harder than on the BT-5. Currently, openings are cut in necessary plates to reduce the time of removal to 30-40 minutes, same as on the BT-5.

On the flushing of water and oil: it takes 9 minutes and 30 seconds to flush water from the BT-5 radiator. It takes 4 minutes and 30 seconds to do it on the BT-7. Performance was not reduced. As for flushing oil, an additional hatch is present on the BT-7 which enables flushing all oil. Currently, instead of iron pipes, red copper pipes are used, which increases the speed of flushing oil.

On shorts in the electrical system: we do not know of any shorts in the electrical system. 

On the bolts and rivets: factory trials of various hardened steels revealed that the best bolts and rivets are made from nickel-chrome steel. The terms for producing nickel-chrome steel bolts are currently being negotiated with ABTU chief comrade Bokis.

On the 6247 and 6411 ball bearings: in some cases, 6247 and 6411 ball bearings produced by the 2nd GPZ did break earlier than imported ones. ABTU requested that all new vehicles should use imported ball bearings. Currently, 6411 ball bearings are imported, and 6217 ball bearings are replaced with 42217 ball bearings from 1st GPZ. These ball bearings show satisfactory quality in trials.

On the T-35 tank:

As a result of 1000 km of trials with a new dust filter, no engine components were worn out. Current production T-35s carry the new air filter.

The same trials revealed no defects in the gearbox. The gearbox works reliably.

The final drices leak when lubricant levels are higher than the grease retainer cork. Currently, a higher density grease retainer is in development. As for a redesign of the final drive, the final drive works reliably, and there is no need for that.

Spetsmashtrest chief Neiman
Factory director Bondarenko

July 25th, 1936"
RGASPI 558-2-142

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