Hit-and-miss Engine - Construction

Construction

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 a buzz coil. A buzz coil used battery power to generate a 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.