Editing M4 Sherman (section)

===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>