|This article relies largely or entirely upon a single source. (January 2010)|
A hit-and-miss engine is a type of four-stroke internal combustion engine that was conceived in the late 19th century and was produced by various companies from the 1890s through approximately the 1940s. The name comes from the method of speed control that is implemented on these engines (as opposed to the "throttle governed" method of speed control). The sound made when the engine is running without a load is a distinctive "POP whoosh whoosh whoosh whoosh POP" as the engine fires and then coasts until the speed decreases and it needs to fire again to maintain its average speed.
Hit-and-miss engines were made by a multitude of engine manufacturers during their peak usage which was from approximately 1910 through the early 1930s when they began to be replaced by more modern designs. Some of the largest engine manufacturers were Stover, Hercules, International Harvester (McCormick Deering), John Deere and Fairbanks Morse.
A hit-and-miss engine is a type of flywheel engine. A flywheel engine is an engine that has a large flywheel or set of flywheels connected to the crankshaft. The flywheels maintain engine speed during engine cycles that do not produce driving mechanical forces. The flywheels store energy on the combustion stroke and supply the stored energy to the mechanical load on the other three strokes of the piston. When these engines were designed technology was not nearly as advanced as today and all parts were made very large. A typical 6 horsepower (4.5 kW) engine weighs approximately 1000 pounds (454 kg). The engine material was mainly cast iron and all significant engine parts were cast from it. Small functional pieces were made of steel and machined to perform their function.
The fuel system of a hit-and-miss engine consists of a fuel tank, fuel line, check valve and fuel mixer. The fuel tank most typically held gasoline but many users would start the engines with gasoline and then switch over to a cheaper fuel such as kerosene or diesel. The fuel line connected the fuel tank to the mixer. Inserted into the fuel line was a check valve which kept the fuel from running back to the tank between combustion strokes. The mixer created the correct fuel/air mixture by means of a needle valve attached to a weighted or spring-loaded piston usually in conjunction with an oil-damped dashpot.
Mixer operation was simple, it contained only one moving part, that being the needle valve. While there were exceptions, a mixer did not store fuel in a bowl of any kind. Fuel was simply fed to the mixer, where due to the effect of Bernoulli's principle, it was self-metered in the venturi created below the weighted piston by the action of the attached needle valve, the method used to this day in the SU carburetor.
Sparks to ignite the fuel mixture are created by either a spark plug or a device called an ignitor. When a spark plug was used, the spark was generated by either a magneto or else a trembler (or 'buzz') coil. A buzz coil used battery power to generate a continuous series of high voltage pulses which were fed to the spark plug. For ignitor ignition, either a battery and coil was used or a "low tension" magneto was used. With battery and coil ignition, a battery was wired in series with a wire coil and the ignitor contacts. When the contacts of the ignitor were closed (the contacts reside inside the combustion chamber), electricity flowed through the circuit. When the contacts were opened by the timing mechanism, a spark was generated across the contacts which ignited the mixture. When a low tension magneto (really a low-voltage high-current generator) was used, the output of the magneto was fed directly to the ignitor points and the spark was generated as with a battery and coil.
Lubrication on these early engines was almost always manual (except for very large engines). Main crankshaft bearings and the connecting rod bearing on the crankshaft generally had a grease cup which was a small container (cup) filled with grease and a cover which screwed down on the cup.
When the cover was screwed down tighter grease was forced out of the bottom of the cup and into the bearing. On very early engines there may have been just a hole in the casting of the bearing cap where lubricating oil would be squirted while the engine was running. The piston was lubricated by a drip oiler that continuously fed drips of oil onto the piston. The excess oil from the piston ran out of the cylinder onto the engine and eventually onto the ground. The drip oiler could be adjusted to drip faster or slower depending on the need for lubrication, dictated by how hard the engine was working. The rest of the moving engine components were all lubricated by oil that the engine operator would have to apply from time to time while the engine was running.
Virtually all hit-and-miss engines were of the "open crank" style, that is, there was no enclosed crankcase. The crankshaft, connecting rod, camshaft, gears, governor, etc. were all completely exposed and could be viewed in operation when the engine was running. This made for a messy environment as oil and sometimes grease was thrown from the engine as well as oil running onto the ground. Another disadvantage was that dirt and dust could get on all moving engine parts, causing excessive wear and engine malfunctions. Frequent cleaning of the engine was therefore required to keep it in proper operating condition.
Cooling of the majority of hit-and-miss engines was by water in a reservoir. There were a small portion of small and fractional horsepower engines that were air-cooled with the aid of an incorporated fan. The water-cooled engine had a built in reservoir (larger engines usually did not have a reservoir and required connection to a large external tank for cooling water via pipe connections on the cylinder). The water reservoir included the area around the cylinder as well as the cylinder head (most cases) and a tank mounted or cast above the cylinder. When the engine ran it heated the water. Cooling was accomplished by the water steaming off and removing heat from the engine. When an engine ran under load for a period of time is was common for the water in the reservoir to boil. Replacement of lost water was needed from time to time. A danger of the water-cooled design was freezing in cold weather. Many engines were ruined by the forgetful operator neglecting to drain the water when the engine was not in use and the water freezing and breaking the cast iron engine pieces. However, New Holland patented a v-shaped reservoir, so that expanding ice pushed itself up and into a larger space, so that the ice wouldn't break the reservoir. Water jacket repairs are common on many of the engines that exist today.
These were simple engines compared to modern engine design. However, they incorporated some very clever designs in several areas, many times because the designer was attempting to circumvent infringing a patent for a particular part of the engine. This is particularly true in the area of the governor. Governors were centrifugal, swinging arm, pivot arm, and many others. The actuator mechanism to govern speed was also varied depending on patents existing and the governor used. See, for example, U.S. Patents 543,157 from 1895 or 980,658 from 1911. However accomplished, the governor had one job - to control the speed of the engine. In modern engines, power output is controlled by throttling the flow of the air through the intake by means of a butterfly valve; the only exception to this being in diesels and Valvetronic petrol engines. On hit-and-miss engines, the governor holds the exhaust valve open whenever the engine is operating above its set speed, thus interrupting the Otto cycle firing mechanism.
The intake valve on hit-and-miss engines has no actuator. It has a light spring that holds it closed until it can be drawn open when a vacuum occurs in the cylinder. Such a vacuum can only occur when the piston is in a down-stroke and when the exhaust valve is closed. (Therefore, when the governor holds the exhaust valve open, the intake valve will not open.) This vacuum causes the intake valve to open, which allows the fuel-air mixture to enter.
Hit-and-miss engines were made to produce power outputs from 1 through approximately 100 horsepower (.75 - 75 kW). These engines are slow speed and typically ran from 250 revolutions per minute (rpm) for large horsepower engines to 600 rpm for small horsepower engines.
They were used to power pumps for cultivation, saws for cutting wood, generators for electricity in rural areas, running farm equipment and many other stationary applications. Some were mounted on cement mixers. These engines also ran some of the early washing machines. They were used as a labour-saving device on farms, and allowed the farmer to accomplish much more than he was previously able to do.
The engine was typically belted to the device being powered by a wide flat belt, typically from 2 - 6 inches (5 - 15 cm) wide. The flat belt was driven by a pulley on the engine that attached either to a flywheel or to the crankshaft. The pulley was specially made in that its circumference was slightly tapered from the middle to each edge (like an over-inflated car tyre) so that the middle of the pulley was a slightly larger diameter. This design kept the flat belt in the centre of the pulley.
By the 1930s, more-advanced types of engines were being designed and produced. Flywheel engines were extremely heavy for the power produced, ran at very slow speeds, required a lot of maintenance, and could not easily be incorporated into mobile applications. In the late 1920s International Harvester already had the model M engine which was an enclosed version of a flywheel engine. Their next step was the model LA which was a totally enclosed engine (except for the valve system) featuring self-lubrication (oil in the crankcase), reliable spark plug ignition, faster-speed operation (up to about 750-800 RPM) and most of all, light in weight compared to earlier generations. While the 1½ HP (1.1 kW) model LA still weighed about 150 pounds (68 kg), it was far lighter than the model M 1½ HP engine, which is in the 300-350 pound (136 - 159 kg) range. Later a slightly improved LA, the LB was produced. The models M, LA and LB were throttle governed. As time passed, more engine manufacturers moved to the enclosed crankcase engine. Companies like Briggs and Stratton were also producing lightweight air-cooled engines in the 1/2 to 2 HP (.37 - 1.5 kW) range and used much lighter-weight materials. These engines also ran at much higher speeds (up to approximately 2000–2500 RPM) and therefore produced far more power per pound than the slow flywheel engines.
With the exception of oil field applications, flywheel engine production ceased in the 1940s.
Although thousands of out-of-use flywheel engines were scrapped in the iron and steel drives of World War II, many survived to be restored to working order by enthusiasts. However in recent years engines with original paint have become more desireable to many collectors than repainted engines. Numerous preserved hit-and-miss engines may be seen in action at shows dedicated to antique engines (many have antique tractors too) as well as in the stationary engine section of steam fairs and vintage vehicle rallies.
- Michael Lawrence Mery, "Explosive engine," U.S. patent 543,157 (filed: Feb. 7, 1895 ; issued: July 23, 1895).
- Theodore C. Menges, "Speed-regulator for internal-combustion engines," U.S. patent 980,658 (filed: Oct. 28, 1909 ; issued: Jan. 3, 1911).
- Harry's Old Engine "Antique gas engine collection" – a wide variety of hit-and-miss engines (different makes, different uses), each with a detailed, illustrated description page, some including audio clips of the engines running
- Description of Novo 6HP engine (manufactured in Lansing Michigan) with video showing engine in operation
- Description of a Fairbanks Jack-of-all-trades engine
- Description of a Jaeger 2HP engine
- Description of a Reid 15HP engine
- Animation of hit-and-miss engine
- Video of large hit-and-miss engine
- Video of small hit-and-miss engine
- "International Harvester Famous 3 Horsepower Hit-Miss Engine" – Description of International Harvester Famous 3 Horsepower Hit-Miss Engine
- Gas Engine Magazine (features) – Enthusiast's magazine covering the history and preservation of hit-and-miss engines