Chrysler's A57 30-Cylinder Tank Engine

In mid-1941, what do you get when the U.S. Army asks Chrysler to build an engine for medium and fast tanks? You get a tank engine so complicated it almost looks like it was designed in Germany. But unlike most German designs of World War II, the Chrysler A-75 Multibank engine worked. This engine became one of the most reliable powerplants the Sherman would use and would surpass in reliability and driveability the R975 engine chosen by the U.S. Army.

Chrysler decided that the quickest way to put an engine into production was to take as much as possible from their already strong line of automotive engines. They chose the 115 hp “Royal” inline six-cylinder. They decided to fit five in a crankcase. They tied the power together with a complicated but very efficient gear train located at the front of each block. The new crankcase included the oil pan. The oil pumping system was changed, with two pumps driven from a shaft that drew power from the new gear train.

The test engines were ready to be installed in the tanks, and testing began in mid-November 1941, on the M3A4, and by February 1942, the M4A4 was testing production engines. The U.S. Army was pleased with the power and driveability of tanks using this engine, although the early engines had many problems. The biggest was overheating, caused by dirt and grease in the radiator. Other major problems were water pump and generator failures. The last complaint was that it was difficult to work in the cramped engine compartment. None of these problems were insurmountable, and Chrysler set about fixing them.

It was discovered that the cooling problems were due to a poorly sealed area around the radiator, insufficiently resistant parts and water pump failures. Individual pumps were abandoned and replaced with a single gear-driven unit. The engine blocks were not designed to sit at an angle, so it was also necessary to re-drill the water jackets to improve flow. Generator reliability problems were solved by moving the generator to the fighting compartment, where it was driven from the driveshaft. They also moved all the carburetors from near the intake manifold to the top of the engine for easier access to the carburetors. Flow problems resulting from having longer intake pipes of unequal length were solved with baffles on the pipes. With these changes, it became as reliable or more reliable than all other Sherman engines except the GAA. The A-57 averaged 240 hours before a serious failure, the GAA 255 hours and the R975 only 218.

The Army had made a decision before Chrysler had fully improved the engine: they wanted nothing to do with it. However, the M4A4 was in production, and to meet tank production targets for 1942, it had to stay that way. So they were used for training in the United States. The British, who wanted M4 or M4A2 tanks were competing for tanks with the Soviets and the French took them and made them work. The Soviets refused to accept them after they sent them two test tanks.

Chrysler and the Army Ordnance Department knew the A-57 was a dead end, they decided to see how far they could improve its reliability and a few more changes would give the A-57 the best reliability in its class. The Army noted that almost all of the A-57's failures were due to piston ring and exhaust valve failures. They installed stellite-coated, sodium-cooled exhaust valves and chrome-plated upper rings, and the A-57 was able to pass the 400-hour, 4,000-mile endurance tests with only one failure in the four-tank tests. No other booster achieved this, and the A-57 was considered the most reliable of the engines in February 1944.

This engine was orphaned in U.S. service. It powered the M3A4 and M4A4. The Army used the engine for training and tried to pawn some off to the Marines. This lasted about two months at the Marine Corps Tank School. The growing need for tanks by the British eventually figured out what to do with the tanks that ended up with this engine. They would end up taking nearly 8,000 of them. Chrysler sent technical representatives to England with these tanks and taught the maintenance crews how to keep them running. This worked well and the engines served their purpose with few problems. They often powered the best pure AT version of the Sherman, the Sherman VC Firefly. This engine was used extensively during and after the war, as many countries received Sherman Firefly's to assist their recovering armies.

This engine was quite robust and would continue to run and allow the tank to move with three of the five banks of cylinders not running. This would leave the tank severely underpowered, but would be useful for taking it to the shipyard or to a dragoon wagon.

Daily maintenance could be done with the engine in the tank, carburetor and timing adjustments, fluids and filters and the like. If something major needed to be fixed, one of the engines had a bad piston or valve, or even something minor like a major vacuum leak in the intake of one of the engines, or even a leak in the cooling system, the whole engine had to be disassembled. Chrysler knew this and made getting the engine out and in as easy as possible, including huge lifting eyes built into the common block to help lift the engine. The British probably had several depots for rebuilding A57 power units that needed major work, and Chrysler made many replacement engines and parts to support the engine.

• The Chrysler A57 Page
  https://www.theshermantank.com/about/the-sherman-tank-engine-page/the-chrysler-a57-page/
• Chrysler A57
  https://wikitanks.com/index.php?title=Chrysler_A57
• Weird Warrior: Chrysler’s A57 30-Cylinder Tank Engine
  https://www.macsmotorcitygarage.com/weird-warrior-chryslers-a57-30-cylinder-tank-engine/