Hit & Miss Engine: Working, common uses and DIY Builds

Have you seen an engine that starts and stops continuously like a person coughing? That’s a Hit & Miss engine– a very old machine that works only when needed, so it saves fuel. 

This guide will explain to you what a hit-and-miss engine is, what it does, where it is used, and how to build one from a simple DIY assembly kit. If you are looking for interesting projects or are a fan of vintage engines, this could be a brilliant starting point. Let's dive in and unleash the power of the engine!

1) What is a Hit & Miss Engine?

“A hit-and-miss engine is a classical four-stroke internal combustion engine that has a fuel ignition system controlled by a governor ( speed controller).”

Unlike today’s engines, which fire on every power cycle, a hit-and-miss engine only fires (or “hits”) when the speed drops below a set level. However, when it reaches or goes beyond that level, it skips the combustion cycle (i.e. “misses”) to avoid overspeeding. Hence, it's named Hit & Miss engine. Clear!

Moreover, Hit and Miss engines were commonly used from the 1890s to the 1940s to power small equipment like water pumps, grain mills, and generators. 

• Key Features of a Hit or Miss Engine

Governor-Based Speed Regulation: First of all, Centrifugal governors, commonly mounted on the crankshaft, are the main components of the hit-and-miss engine. This system allows accurate control without the use of complicated electronics, maintaining a target speed range of ±20 RPM.

Intermittent Combustion Cycle (Hit and Miss Action): A modern four-stroke engine experiences a power stroke every two revolutions. On the other hand, with the hit-and-miss engine, it can skip several cycles before firing again, depending on the load. This atypical combustion pattern simultaneously saves fuel and reduces mechanical wear. 

Large, Balanced Flywheels: In addition to accommodating the irregular power delivery, hit-and-miss engines incorporate huge flywheels. These flywheels capture kinetic energy ( energy due to motion) during power strokes and release it during inertia cycles (engine running without firing) to ensure more uniform rotation and maintain momentum.

Low RPM and High Torque: Furthermore, Hit and miss engines have very low operating speeds, usually between 300 and 600 RPM, but provide high torque( force that causes it to rotate) at low RPM, which is needed for driving belt-driven machinery. 

Basic Mechanical Engineering: Last but not least, the majority of hit-and-miss engines have a frame made of cast iron, a mechanical valve train, and a prominent push rod aggravation. Because of the open construction of the engines, understanding, repairing, and modifying the engines is easy. 

• Overview of the Technical details of the Hit and Miss engine

2) How a Hit and Miss Engine Works?

Before moving ahead, it’s essential to keep in mind that a hit-and-miss engine runs on mechanical frameworks such as inertia, combustion timing, valve action, and speed control. These elements work together to perform a four-stroke internal combustion cycle – intake, compression, power, and exhaust. 

To appreciate its workings, it is crucial to get familiar with its main parts.

     Major Parts and Their Functions  

• Flywheel: It is usually Hefty & large and retains rotational energy. This energy sustains the crankshaft during the non-firing (miss) cycles.  

• Governor: It’s a mechanical unit with rotating flyweights, controlling the speed of the engine.  

• Ignition System: This part usually consists of a spark plug connected to a magneto or battery, which ignites the fuel-air mixture.  

• Fuel System: This system issues gasoline or kerosene to a carburettor, which injects fuel into a cylinder mixed with air.  

• Valves and Piston: The piston squeezes the mixture, and valves regulate the entry and exit of air to the combustion chamber.
  

    Step-by-Step Working Procedure

Now, let's see how the above-mentioned components work together to drive the engine!

Step 1) Intake Stroke 

At the initial stage of operation, the engine is activated, and the piston moves downward position and the crankshaft begins to rotate as well. During this phase, the inlet valve becomes wide open, allowing a mixture of fuel and air to enter the system from the carburettor. Keep in mind that the engine has not fired yet, we can say that it is only seeking to prepare the right mixture for a later process of combustion. 

Step 2) Compression Stroke 

Now, the piston compresses the mixture of air and fuel by moving in an upward direction. With the inlet and outlet valves closed, the pressure increases, thus the compressed fuel mixture becomes ignitable.

As discussed earlier, the compression ratio is low in hit & miss engines, so air-fuel mixtures didn’t get too compressed. Thus, it puts low stress on engine parts and enables it to run efficiently without causing damage or knocking problems. 

Step 3) Power Stroke (Hit)

When the piston is at Top Dead Centre (TDC) position, it is almost at the top, and the spark plug ignites the mixture. The force accompanying the explosion pushes the piston down, turning it along with the crankshaft, generating power. The energy is captured while the flywheel stores the energy, which will assist the engine to maintain rotation when it isn't firing. 

Step 4) Exhaust Stroke 

Once again, the piston moves upwards, and this time the exhaust valve opens. Thus, the residual fuel or say left-over burnt gases from previous combustion chambers are usually pushed out. Thus, the one cycle gets completed and it makes it ready for the next intake stroke and vice versa.

• Governor Control:

The governor serves as a mechanical gadget observing the speed of an engine. It is made up of a collection of rotating weights, or flyweights, which respond to speed changes.

As the engine speed increases, centrifugal force pushes the flyweights outward which in return, increases tension on the spring, and which in return forces the intake valve to remain close so no fuel can go inside and hence no power stroke.

On the other hand, when the engine speed decreases, flyweights move inwards. As a result, the tension on the spring decreases, and the intake value open as usual to provide more fuel. Thus, this system is very helpful in self-regulating the engine's speed, and controlling the fuel consumption with the engine functioning only when required. 

3) Common Uses of Hit and Miss Engines 

Hit and miss engines' remarkable capability to operate on low-quality fuel, refined construction, and unmatched efficiency made them a must-have in the early 20th century. In this section, we’ll discuss both historical and modern uses!

• Historical Uses

Powering Irrigation Systems: Back in the days, one of the most innovative roles on hit-and-miss engines was powering water lifts. These engines were a trustworthy means of water supply for irrigation, livestock, and households on farms, specifically in rural regions where electricity was non-existent. Thus, this was immensely helpful for people working in agriculture.

Driving Mechanical Devices: Aside from pumping water, such engines also aided in driving numerous mechanical devices. Various workshop devices such as sawmills, corn grinding machines, as well as feed cutting machines, relied on Hit and Miss Engines. 

Supportive Farm Machinery: In addition to the above, on farms, hit-and-miss engines powered machinery like cream separators and butter churns, along with grain mills. Agricultural tasks were simplified and streamlined with these engines, which helped to mechanize farming around the early 1900s. 

Moreover, some engines were adapted to power early washing machines and other household appliances, thus assisting with household chores.

• Modern Applications 
  

Restoration and Engine Exhibitions: Currently, antique hit-and-miss engines have stopped being used for routine tasks, but they now have a purpose in the restoration and exhibition world. These engines are collected and restored by numerous hobbyists and then exhibited at antique engine shows, where the mechanical cycles and peculiar sounds of the engines are demonstrated.

Teaching Demonstrations: In teaching environments, hit-and-miss engines can serve as illustrative examples for combustion engines. They are used in classrooms to illustrate combustion, valve timing, and the working principles of a governor—key concepts necessary for understanding the operation of engines.

Applications of Off-Grid Power: Unlike most users, a small segment of the modern populace has repurposed hit-and-miss engines for off-grid power usage. These engines can provide power to small remote systems and serve as a charming alternative to contemporary electrical solutions.

4) Building a Hit and Miss Engine Using a DIY Engine Kit: A Step-by-Step Guide

Now, you might be wondering whether you can build such an engine at home or not. If so, then be patient! Whether you are a novice or a pro hobbyist, you can easily do this project by utilising an EngineDIY model kit. We specialise in providing DIY engine kits at affordable prices to boost creativity among students or enthusiasts. So, let's have a look at how you can make this engine model by utilising the DIY Kit!

（1）Prerequisites

Safety Considerations: These projects are very fulfilling and satisfying. However, you should make sure you are putting on the right protective equipment. Towards the start, make sure everything is in protective gear like gloves and safety glasses as well as hearing protection. 

Moreover, be in a properly ventilated space when working with fuel and ignition systems, and adhere to safety guidelines before working with the kit.  

Mechanical Aptitude: Even though a set of instructions will be readily available, having background knowledge of some mechanical systems will be a great advantage. Moreover, I must say that familiarity and comfort with all basic tools like screwdrivers and wrenches is a great place to start.

Tools and Space Required: In addition, your workspace should be orderly with sufficient lighting. Make sure the workbench is large enough to hold all the components. The following are the tools required for a hassle-free build: 

• Three hexagonal socket wrenches 

• A socket with 8mm width
  

（2）Components included in the DIY Model Engine kit

Your DIY kit usually contains all the parts to assemble a functioning hit-and-miss engine. However, the primary parts comprise: 

• Flywheel 

• Governor 

• Spark plug

• Valves (Both intake and exhaust) 

• Fuel tank 

• Carburetor 

• Ignition system (magneto or battery ignition) 

• Crankshaft 

• Piston 

• Connecting rods 

• Bearings

• Valve springs

• Cylinder head 

• Fuel lines and fittings 

• Gaskets 

• Engine block or base (aluminium or cast iron) 

• Weights and springs of the governor

• Components of the lubrication system 

• Timing gear or mechanism  

• Throttle linkage (only if applicable)

• Parts of the exhaust system

（3）Basic Tutorial for Assembly:

Step 1) You have to start by going through the instructions and blueprints that were sent alongside the kit. Keep in mind that effective planning ensures that all parts will be assembled in the right order.

Step 2) Well! First of all, you have to screw the base or block of the engine into the wooden frame. Next, you have to take gear ( controlling the inlet, exhaust valves and also ignition systems ) and also the holder and fit holder into the centre of gear just by rotating.

Step 3) Then you need to screw the gear fitted with a holder into the engine placed on a wooden frame as shown in the picture below.

Step 4) After this, you will take a crankshaft, two small bearings and a piston with an inserted connecting rod and fit them together using screws. Here keep in mind that piston should freely move, so it's always advisable to put oil on moving parts for smoother running.

Step 5) Now, you will fit the piston attached to the crankshaft to the engine. While inserting this, you will see a small hole on the tooth of the large gear attached to the engine and also on the crankshaft tooth between two grits. So you have to ensure these two points fit together otherwise timing will not match.

You need to check again and again that the piston is smoothly moving or not, Okay!

Step 6) After this, you’ll mount the flywheel. To do this, firstly, you need to screw the drum onto the flywheel. Then, we'll tighten the flywheels on both sides of the crankshaft’ rode.

Step 7) Next, you’ll set the valve rod using a spring and tighten it a little bit.

Step 8) Place the cylinder on the base and ensure the piston is able to slide within it.

Step 9) Now, attach the carburettor, and place the fuel plastic hose at the bottom.

Step 10) Also attach the exhaust with the top silver plate.

Step 11) At this stage, insert the oil tanker and fill it for larger operations and be cautious. Now, it's all done just check the alignment and attach a battery.

Step 12) Lastly, you need to conduct a final checklist with all the components to ensure every system is working. You have to confirm that the flywheel, piston, and valves rotate smoothly and check that the engine functions correctly under the hit-and-miss test.  

（4）Troubleshooting Tips  

i) Common novice errors include:  

• If the engine is not shifting between hits and misses, the governor may not be set correctly.  

• Make sure all joints between the fuel lines, fuel tank, and carburettor are leak-proof. 

ii) Maintenance Recommendations  

Moreover, it is highly recommended that you lubricate the governor and crankshaft regularly. For optimal combustion, make sure to clean the carburettor and change the spark plug.

5) Final Words

Based on all the insights provided, it can be concluded that the Hit and Miss engine is one of the coolest historical technologies, wonderfully engineered with modern do-it-yourself opportunities. From educational exhibitions to constructing one yourself, it is definitely a fulfilling project.

Anyone looking forward to this do-it-yourself project, thinking of buying from EngineDiy, is a good idea. We offer the best budget-friendly DIY kits that require no extra effort and help stimulate learning. So, get in touch with us today and empower your creativity!

6) FAQs related to Hit & Miss Engine

i) Is there a possibility to build a Hit and Miss engine at home?

Yes, definitely, anyone capable of following the directions step by step can assemble Hit and Miss engines at home using the prepackaged parts in a DIY engine kit.

ii) How do I maintain a Hit and Miss engine?

Ensuring regular lubrication, carburettor cleaning, and spark plug replacement when required ensures smooth functioning of the Engine.

iii) What are the Hit and Miss engines made of?

Brass and thin steel, along with the heavy cast iron, are major components in the engine block, crankshaft, and smaller details encompassing the valves and the governor.