Engine and Drivetrain
68 All of the initial Jeep prototypes were powered by 4-cylinder engines because using a 6-cylinder engine would have resulted in a vehicle that was much too heavy to meet the army’s strict weight requirements. Bantam fitted its vehicle with a 40-hp Continental engine that was popular in lift trucks; the Ford GP was fitted with a Ford tractor engine good for 40 hp. Willys used the same four-banger that was in its passenger cars. The Willys’ mill was a rugged, durable 134.2-ci engine that developed 60 hp at 4,000 rpm and 105 ft-lbs of torque at just 2,000 rpm, which meant it was ideal for lugging along in low range yet also capable of fairly high road speeds. The Willys engine’s compression ratio was 6.40:1, meaning the doughty little Jeep could easily run on low-quality gasoline without knock or pinging.
69 The Willys engine originated in the 1926 Whippet, a line of popular, low-priced cars built by Willys-Overland during the late 1920s and early 1930s. Developing just 30 hp at the time, the little flathead mill was fine by the standards of 1926, but sadly out of date by 1938, when it was still being used in the new Willys 48 small car.
By that point, output had been boosted to 48 hp, but the engine was noisy, rough-running, and had a well-earned reputation for being short lived. The engine tended to wear out its bearings, burn pistons, and throw rods. It had a lot of problems.
70 That bad reputation was holding down sales. Who wants to buy a car with a tired, weak engine? So during 1939, the company’s management ordered the engineering department to do something about it. Engineering vice president Barney Roos, assisted by an extremely capable young engineer named Floyd Kishline, decided to go through the engine and fix the problems one by one.
The two men found many; in the end they had to redesign the engine block to give it full-length water jackets for better, more even cooling; design a new cylinder head; engineer a new carburetor and intake and exhaust manifolds for better breathing; design better valves, water pump, bearings, pistons, air cleaner, timing gears; and much, much more. It involved a lot of work and a lot of testing, but in the end, Roos and Kishline created essentially a new engine without the extreme expense of all-new tooling.
Engine output rose from 48 hp to 60 hp, a solid 25-percent improvement, and the engine ran much smoother and quieter. At the same time, durability was vastly increased. Prior to the redesign, a stock Willys 4-cylinder engine run at full throttle usually burned out in about four hours; that’s how bad the engine was. By the time Roos was finished with it, the redesigned engine ran 100 hours or more at peak rpm with no damage.
The Roos-Kishline redesign effort made the Willys engine the most powerful and most durable four-banger in America. They called it the Willys Go-Devil. It went on to become a legend and remained in production for decades.
71 The MB’s transmission is a T-84 3-speed manual gearbox that was produced by Warner Gear. The transfer case is a 2-speed unit manufactured by Spicer Manufacturing Company, which later was renamed Dana Corporation. Some sources report that the Brown-Lippe company also supplied transfer cases to Willys-Overland.
Army test drivers were told to drive the test Jeeps until something broke, then report the problem to Willys, which would then engineer a stronger replacement part. The result was a light but extremely strong vehicle that could be produced for a relatively low price.
72 The Spicer 25 front axle used on the wartime Willys Jeep MB is a full-floating design combining the stability of a hypoid design with steerable front knuckles at the outer ends of a rigid axle housing. This combination provides good maneuverability and outstanding durability in off-road situations.
73 As sturdy as the Willys Jeep was, during early prewar days the test drivers at Camp Holabird were tougher, running the test vehicles around the clock with specific instructions to keep pounding them until something broke. One test Jeep suffered a cracked frame at 5,184 miles; another had its engine cylinders so badly worn out by 5,011 miles that the engine had to be replaced. The army had no spare engines on hand, so a couple of enterprising mechanics from Willys-Overland pulled the engine from a civilian Willys car in the parking lot!
Other problems that showed up in early testing included transfer case main bearing failures, steering pin failures, and several spring and suspension failures. The army testers forwarded their report to the Quartermaster General, who told Willys it better fix the problems if it wanted to keep the contract. Barney Roos, Willys vice president of engineering, conferred with suppliers and with Willys’ own manufacturing people and ordered them to beef up the weak parts ASAP.
74 A report found in the files of Willys-Overland refers to a wartime effort to produce a Jeep without a carburetor. Exactly how that would have worked isn’t mentioned, and I wonder if the test reports on that effort are stowed away in some obscure file at Jeep.
75 In addition to all of the Jeep vehicles it produced for World War II, Willys also produced 83,000 Go-Devil engines that were mounted and used as stationary power units and electrical generators. The company also produced the Robomb (rocket-bomb), which was the US Army’s answer to the German V-1 and V-2 rockets.
The military chose the Willys Jeep MB to be the standard Jeep for the armed forces and contracted with Ford to produce them. The Ford units are dubbed GP-W (for General Purpose) Willys. The MBs and GP-Ws are nearly identical and were designed for easy shipping.
76 By 1952, the Go-Devil was once again out of date and in need of replacing. The new Jeep M38 (Willys MC) weighed about 2,750 pounds and fully loaded could weigh just under 2 tons, which is a very heavy load for 60 hp to pull. So, when the M-38A1 was being developed, increased horsepower was ordered.
Willys management was still extremely frugal with capital investments and didn’t want to shell out the money for an all-new engine, so it instructed its engineers to somehow squeeze more juice out of the aging Go-Devil. Willys’ chief engineer Barney Roos and engineer A. C. Sampietro (Floyd Kishline had left the company) went to work on the little mill. Sampietro designed a new F-type cylinder head for the Willys mill that boosted output to 72 hp, another 20-percent boost.
77 Okay, so you’re asking: What exactly is an F-head? It’s an engine with one valve in the block, similar to an old-style L-head (or flathead) engine, and one valve in the head, similar to an OHV engine. It provides much better breathing compared to a flathead engine and thus more power. It’s a relatively cheap way to boost power in an old-style engine.
78 The little Willys Whippet 4-cylinder engine, introduced for 1926, remained in production through at least 1971 for the United States, and even longer in export markets. It became the Go-Devil engine in 1938 after Willys’ engineers went through it with a fine-tooth comb, ironing out all its bugs. Then it received another large power boost with the introduction of the F-head Hurricane version in the 1950s.
It was offered in nearly all of the postwar Willys vehicles. After Kaiser Motors took over the company, it was kept in production as the standard engine on all Kaiser Jeep CJ Jeeps, and even for the DJ-5 and DJ-6 models, as well as the Jeepster Commando series, despite it being sorely out of date by then. I asked a retired Kaiser Jeep vice president why the company continued to produce the hoary old Hurricane for so long when it was out of date, and he replied, “We did it simply because it was very cheap to make.” Oh.
This experimental multifuel engine was designed and built by Willys Motors’ engineers for the military. The goal of using multifuel engines was to make it easier to obtain and use different fuels in forward areas where gasoline might not be available, but diesel or kerosene was.
79 The 1950–1951 military M38 Jeep (also known as the Willys MC) still had the classic flat fenders up front but was given a stronger Spicer 44 rear axle and sturdy timing