Editing M4 Sherman (section)

==Reliability==
{{Page numbers needed|section|date=September 2021}}

===M4A1===
In September 1942 the British developed some potential improvements and tested the tanks.<ref name="Archive Canadian Military Headquarters 1947">Archive Canadian Military Headquarters, London (1939–1947) RG 24 C 2</ref>{{sfn|Hunnicutt|2015|p={{page needed|date=September 2021}}}}

After {{convert|805| km|abbr=on}} the springs of the left front bogie broke, considered typical for this type of suspension. Oil accumulated on the floor of the engine compartment during driving. The engine periodically stalled under high load due to interrupted fuel supply. It was found that the engine had been built and installed incorrectly. Upon disassembly carbon deposits were found on the working surfaces of the cylinders; they were very worn out after only 65 hours of operation or {{convert|702| mile|abbr=on}} run. In the absence of a replacement by 10 October, the engine was put back in the tank; the revised fuel system was supposed to improve the stalling engine.

In November 1943, several M4A1 Shermans were tested at the American proving ground to test British innovations. On one of them, 37 experimental changes were made, on the second – 47, on the third – 53. In total, 60 changes were developed and implemented for the Shermans, most of which were considered successful after a 600-mile run and firing.<ref name="Archive Canadian Military Headquarters 1947"/>

===M4A2===
In Africa, the British engines ran for 700–900 miles (1130–1450&nbsp;km), or 180–200 hours. The engine had to be inspected and repaired after 100 hours, which significantly extended its service life, but there was not enough time for such work, and among crews, it was believed that there was little benefit in the procedure. The engine left much to be desired, as evidenced by attempts at modifications in the Eighth Army, which did not affect the reliability of the tank.<ref name="Archive Canadian Military Headquarters 1947"/> The Shermans also had other defects, including broken wiring, breaking ignition coils, and clutch rods.

The improved return roller design performed much better than that which the early Sherman production inherited from the M3. A February 1943 report described a unit where there were no broken bogey coil springs even after a 1,000-mile (1,600&nbsp;km) march. The tracks however suffered; the rubber flaked off and after a run of 600 miles (970&nbsp;km) the tracks were unusable. Some units rode on tracks without the rubber pads, but the rubber tires of the rollers wore down faster. The introduction of radially grooved tires helped to cope with overheating when driving fast in the desert, but de-lamination of the tires still led to cracks in the rollers after 300 miles (480&nbsp;km).

The<!-- Sherman Mk.III --> M4A2 performed very well in hot climates in general. The British sent as many of these as possible to the Mediterranean theater, retaining a minimum of vehicles for training in the UK. Complaints began to come in about carbon fouling of the [[Fuel injection|injectors]] due to oil getting into the combustion chamber.

Other mechanical problems were rare and were most common in the left engine. Shermans suffered from wear to tire trackpads which were mitigated by changing to all-metal tracks and ventilated rollers. The tanks proved to be very reliable with proper operation. In June 1943, it was noted that the average service life was estimated at 1,500 miles (2,400&nbsp;km). The M4A2 was rated "very high", while the M4A1 was rated "high".<ref name="Archive Canadian Military Headquarters 1947"/>

The Soviet [[6th Guards Tank Army]] determined the lifespan of their M4A2 Shermans to be {{convert|2000|to|2500|km|abbr=on}} or 250–300 hours, comparable to the T-34.<ref>{{citation |title=CAMD RF 500-12462-93 |work=Soviet Era Documents |publisher=Federal Archival Agency (Russia) |language=ru}}</ref>

===M4A3===
The Ford V-8 engined M4A3s took part in the 1943 'survival' race. On average, the engines worked for 255 hours, though one failed after 87 hours of running. Three tanks were taken out of the test at 187, 247, and 295 operating hours due to reasons unrelated to the engine. The report noted that even disqualified motors could be returned to service by replacing only one part: the rest were still in excellent condition. Of all the Ford engines, it turned out to be the most service friendly. The M4A3 tanks covered a greater distance than other Shermans: ten vehicles covered 20,346 miles (32,743&nbsp;km) in total (half on-the-road, half off-road) over 2,388 hours - an impressive achievement.

The M4A3 continued to lead to reliability through further testing. On tests in the winter and spring of 1944, one tank covered {{convert|2,097|mi|abbr=on}} in 203 hours and 25 minutes. An M4 failed after only 15 hours and 10 minutes and was replaced by another. The M4A1 lasted 27 hours 15 minutes, and the M4A4 covered 1,343 miles (2,161&nbsp;km) in 149 hours and 35 minutes.

Around the same time, another reliability test began, albeit on a smaller scale of 20 Shermans of various types including four M4A3. The time spent on repairs was carefully measured: on average, the M4A3 took 110 hours to service the engine, which was better than the M4A1 (132 hours) or M4A2 (143 hours), but more than double the average of 45 hours on maintenance of the Chrysler multibank by M4A4 crews. M4A3 remained superior in transmission time: 112 hours versus 340 hours for the M4A4. In terms of suspension, the tanks turned out to be approximately equal. None of the tanks with Ford engines passed the entire route: they dropped out after 293, 302, 347, and 350 hours of running. Only three Chrysler engines and one General Motors diesel engine coped with the task.

Although M4A3s were not in service with other armies, some were supplied to the Allies for review. In early January 1943, a new M4A3 was provided to the British Fighting Vehicle Proving Establishment. By 16 January, it began trials. The engine failed after 495 miles (800&nbsp;km). A new engine was delivered by the end of February. This gave more power and better performance and despite multiple problems, the tank achieved 2,000 miles (3,220&nbsp;km). The British considered the M4A3 a very reliable tank but far from perfect. An upgraded vehicle was tested in the spring of 1944; it covered over 3,000 miles (4,863&nbsp;km) through several defects accumulated over the course of the run. The M4A3 was considered an outstanding vehicle for its reliability.<ref name="Archive Canadian Military Headquarters 1947"/>{{sfn|Hunnicutt|2015|p={{page needed|date=September 2021}}}}<ref name="ReferenceC">Pat Ware. M4 Sherman Tank Owners' Workshop Manual: 1941 Onwards (All Variants) – Zenith Press, 2012</ref>

===M4A4===
In October 1942, five M3A4s and five M4A4s were tested in the California desert, which was a monstrous test for vehicles with an unsatisfactory cooling system. Constant breakdowns of auxiliary engine units put an end to the tank's combat career in the US Army. By the spring of 1943, the recommendations given by the Armored Council had been implemented, and 10 M4A4 tanks had been driven to a 4,000-miles (6,440&nbsp;km) range. The average service life of the A57 engine reached 240 hours. M4A4 tanks took second place in reliability after the M4A3 with a Ford GAA engine (255 hours), ahead of diesel M4A2 (225 hours) and M4A1 radial (218 hours). The M4A4 was the easiest to maintain.

Additional tests of four M4A4s from 8 October 1943, to 14 February 1944, showed even better results: one engine broke down after 339 hours, three others worked 400 hours with less than 10% power loss. 3 out of 4 M4A4 could finish the Armored Council test and drive for 4,000-miles (6,440&nbsp;km).

Despite the positive outcomes of additional testing, oil and fuel consumption was still too high for the engine to be recommended for service in the American army. Production of the M4A4 was discontinued on 10 October 1943, and it was declared obsolete in 1945.<ref name="ReferenceC"/><ref>Record of Army Ordnance Research and Development in WWII: Ordnance Development of the Chrysler A-57 (Multi-Bank) Tank Engine</ref>

===Engine===
{{More citations needed section|date=July 2023}}
The M4 Sherman used four different engines, each of a very unique type. Diesel M4A2s had a significant superiority over the [[Wright R-975 Whirlwind|R975 gasoline engines]]. The first M4A3 tank with a [[Ford GAA engine|Ford GAA]] V8 gasoline engine, surpassing the R975 in all aspects, was assembled in May 1942, and even the M4A4 had a more reliable engine.{{sfn|Hunnicutt|2015|p=267}}

[[File:Continental R-975 (side) of a Sherman tank.JPG|thumb|[[Wright R-975 Whirlwind|Continental R975]] aircraft engine used in M4A1]]
The R975 engine began to lose relevance once the vehicle was put into service. The R975 was initially powered by high-octane aviation gasoline. With the entry of the United States into the war, it was necessary to change to a lower grade fuel. To maintain performance, the maximum octane number of fuel for the new engine was limited to 80. In April 1942, an engine with a compression ratio of 5.7 was tested, which was considered acceptable. The nominal revs increased from 1200 to 1800 per minute. The new engine used a richer fuel mixture and had a larger combustion chamber.

Engines were compared in large-scale tests at the Aberdeen Proving Grounds in the winter of 1943–1944 with four examples each of M4A1, M4A2, M4A3, and M4A4. The endpoint was 4,000 miles or 400 hours run time. Faults with anything except the motor were repaired and testing resumed; only critical damage or loss of a third of its original power took the engine out of the competition.

During the tests, it took 132 hours to service the R-975 in the M4A1, 143 hours for the GM diesel M4A2, 110 hours for the Ford GAA M4A3, and 45 hours for the [[Chrysler A57 multibank|multibank]] M4A4. None of the R975 engines reached the 200 hours mark, failing on average after 166 hours.{{efn|The M4A1 tank also required an average of 36 hours of transmission maintenance, 93 hours of chassis maintenance, and a little over 20 hours of other maintenance.}} It was noted that a lot of time was spent on servicing the air filters for the R-975; over 23 days of testing, 446 man-hours were spent on cleaning and repairing them.

An M4 with the R975-C1 engine was tested a year later over a 5,000-mile (8,050&nbsp;km) test in which the engine had to be replaced three times. In addition, there were transmission and suspension problems. The filters performed poorly: it was noted that sand and dust severely spoil the engine and other units.

Work to improve the reliability of the R975 engine led to quite significant changes, resulting in the R975-C4. Engine power increased from {{convert|432| to| 493| hp|abbr=on}}, and fuel consumption decreased by 10%. The engine torque went from 1800 Nm at 1900 pm to 2040 Nm. Older engines were upgraded to the later model during a major overhaul.

[[File:Engine no 5157507 pic1.JPG|thumb|GM 6046 diesel [[U engine]] used in M4A2]]
The new engine was approved for production on 17 June 1943, with 200 units ordered for the [[M18 Hellcat|gun motor carriage T70]] tank destroyer. In October 1943 the British demanded that it be provided for their Shermans. Tests in February 1944 on the M4A1 tank that as well as increased power: oil consumption dropped by 35% and cylinder temperature by 50&nbsp;°C.

The speed increased: the M4A1 with the new engine covered 1.5 miles (2.4&nbsp;km) of paved track in 4 minutes and 45 seconds – 47 seconds faster than the tank with the R975-C1 engine. Tests have also shown increased reliability. The three new R975-C4s installed on the M4A1 were withdrawn from testing after 177, 219, and 231 hours, respectively, and the R975-C1, upgraded to the C4 standard, worked 222 hours on the M4 tank. Compared to its predecessor, the service life of the engines has increased, albeit only slightly.

In 1943, the Americans conducted large-scale trials of all types of Shermans. In total, 40 tanks were admitted to them: 10 each M4A1, M4A2, M4A3, and M4A4. The target was 400 hours or 4000 miles before the engine failed. The rest of the tank units could be repaired an unlimited number of times.

By 23 April 1943, ten M4A2 had covered a total of 16,215 miles (8229 miles on-road and 7,986 miles off-road), operating for 1,825 hours. Fuel consumption of the M4A2 was lower than that of other Shermans: 1.1 mpg (214 liters per 100&nbsp;km) on the highway, and 0.5 miles per gallon (470 liters per 100&nbsp;km) on off-road. On average, tanks consumed 0.81 quarts (0.76 liters) of oil per engine hour. The tests ended on 11 May. By that time, the M4A2 had covered 22,126 miles, running 2,424 hours. The average speed of the M4A2 was the fastest at {{convert| 9.5|mph|abbr=on}}. The M4A1 and M4A4 both made {{convert|8|mph|abbr=on}}, while the M4A3 made {{convert| 9.25|mph|abbr=on}}.

[[File:Chrysler multibank.jpg|thumb|[[Chrysler A57 multibank]] engine used in M4A4]]
In terms of reliability, the M4A2 was in third place. The first engine failed after 75 hours of operation. Two engines worked all 400 hours, while one was in good condition, and the other was on its last legs. On average, the engines worked for 225 hours before the breakdown of the internal units. Only the R-975 engines showed themselves worse than the GM 6–71 (average service life of 218 hours). Ford GAA (255 hours) and Chrysler A57 (240 hours) proved to be more reliable. In terms of time spent on maintenance, the M4A2 came in second.

The tanks continued to race for survival. At the end of 1943, 20 vehicles entered trials at once: four M4A1, M4A2, M4A3, M4A4, and new M4E1 with an experimental engine. The Shermans drove on three types of surfaces: fine loose sand, clayey stony ground, and highways. As in previous tests, during the run, the repairmen could change any units, and only the breakdown of internal components and engine parts disqualified the tank.

By 27 December, all M4A1s (average mileage of 166 hours) and one M4A3 were out of order, but not a single tank with a diesel engine. By 18 February, tests for the M4A2 ended. Three tanks failed after 276, 278, and 353 hours, respectively, while one covered 4295 miles in 403 hours and was still on the move. From M4A3, one tank also remained on the move, but with a rather modest mileage, since it had been under repair for a long time. Of the four M4A4s, one tank broke down, and the M4E1 was removed from testing – it was decided that the RD1820 engine would not go into a large series anyway.

By 18 March, the tanks had finished testing. The M4A4 turned out to be the most reliable again: out of four tanks, three reached the finish line. The M4A4 engine also took the least time to service: 45 hours per tank. M4A2 was in second place, as the last M4A3 still broke down, and did not cover the required distance. However, the maintenance of the GM 6–71 engine took 143 hours – more than the M4A3 (110 hours) or M4A1 (132 hours). The M4A2 also did not shine in servicing the transmission group: it took 220 hours to take care of each tank (only the M4A4 with 340 hours did more). In terms of suspension service time, the tank was at the level of other "Shermans": 205 hours. A total of 327 hours of a run of the average diesel Sherman took 594.5 hours of mechanics' work.<ref name="Archive Canadian Military Headquarters 1947"/>{{sfn|Hunnicutt|2015|p={{page needed|date=September 2021}}}}<ref name="ReferenceC"/><ref>Defense Technology Information Center (DTIC) Archive</ref>