What Is an Interference Engine & How Does It Work?

Introduction

Engines are fascinating and open up a whole new world of creativity. But before understanding one of the major types of engines—interference—it is always good to go back in time.

Though not clearly stated in history, Archimedes may be the father of modern-day engines. It resulted from the comprehensive efforts of various engineers and mathematicians. The most notable are John Barber, Thomas Mead, and Robert Street. The first two patented gas turbines and gas engines in 1791 and 1794, respectively. Street, on the other hand, is credited for inventing an internal-combustion engine which was also the first engine to use liquid petroleum in 1794. The same year, François Isaac de Rivaz, a Swiss engineer, built a hydrogen and oxygen-powered engine.

This convoluted story goes all the way to the modern interference engine. Read more about it down below.

What Is an Interference Engine?

“Interference engines” is an uncommon term in automobiles; thus, understanding it requires a bit of explanation. Normally, an engine has pistons, spark plugs, and two sets of valves, all arranged on a golf-like tee. As the engine runs, one set of valves known as intake valves lets in a mixture of air and fuel, which is then compressed by the piston before being ignited by the spark plug. Of course, igniting compressed fuel will combust the mixture and explode, pushing the piston outward. As that happens, a set of exhaust valves opens to let out gasses.

In an interference engine, the mode of operation is slightly different with respect to how the piston moves. In this type of internal combustion engine, the piston travels to an area occupied by a partially or fully open valve, or the piston overlaps with valves. In contrast, the piston will not travel into this area in a non-interference engine.

From the definition, we can infer the term interference to trespassing, meaning that a piston is trespassing into the valve’s area.

For an interference engine to work, the opening and closing of valves and the piston strokes, among other parts moving in rapid succession, should be synchronized perfectly. This is to prevent the piston from striking an open valve. To achieve that, engine manufacturers use timing gears and a set of chains and belts.

Where Is an Interference Engine Used?

It is understandable that you might be surprised if a small part, like the timing belt, breaks and result in critical failures, yet it is a popular engine. What you are forgetting is that its high compression has led to companies like Nissan, Hyundai, and Honda completely relying on interference engines.

They are also common in factories relying on 4-stroke engines to power operations, with the main advantage being a high compression ratio.

How Does an Interference Engine Work?

An interference engine converts chemical energy from fuel to mechanical energy through combustion. And as an internal combustion engine, the ignition and combustion occur inside fixed cylinders.

The process begins when the intake valve lets in a fuel/air mixture from a carburetor. The carburetor atomizes and vaporizes gasoline before mixing it with air in a determined ratio.

The piston then compresses the mixture before a spark plug ignites it. The resulting explosion pushes the piston outward (power stroke), and through a system of gears and drivetrains, this force is directed to the wheels to drive the car.

The exhaust valve then opens to let out expanded gasses, completing the cycle, and as soon as it closes, a new cycle begins.

In a four-stroke engine, all pistons are always at different stages of the cycle—one may be drawing in air, the other taking out exhaust gasses, and the remaining two in compression and ignition stages. With at least one piston moving drivetrain, a four-stroke engine supplies power to the vehicle consistently and uniformly.

Advantages of an Interference Engine

Higher compression has long since been preferred as the main advantage of an interference engine. This is because there is a positive relationship between high compression and improved performance, especially in diesel engines. That is why almost all diesel engines are interference. Other pros include:

Disadvantages of an Interference Engine

The main disadvantage of these engines is that they are susceptible to critical failures when one component of the timing system fails.

This is because when the gear is timed incorrectly causes the piston to collide with the valves. The piston’s immense power may likely bend or break off the valve. If one of the broken pieces finds its way into the cylinder, it will cause extensive damage requiring engine replacement.

In addition, they require frequent maintenance that may be costly.

Why Does an Interference Engine Achieve a High Compression Ratio Compared to Non-Interference?

Once a piston starts compressing the fuel-air mixture, it reduces the mixture’s volume. By dividing this volume and the total volume of the cylinder, engineers get a compression ratio. Thus, the compression ratio is the ratio between the volume of the combustion chamber and the cylinder.

Racing cars’ engines have a compression ratio of up to 14:1, which implies the car sucks most energy out of the combustion process. Thanks to an interference engine’s design, this high compression ratio, fuel economy, and high engine output can be achieved easily.

First, the car has large valves which open deep inside the combustion chamber to facilitate “breathing.” This improves the rate at which combusted gasses are expelled, increasing the engine’s efficiency.

Second, the combustion chamber is small. The ability of the piston to pass by the valve’s area to compress further the fuel/air mixture reduces the combustion chamber’s volume. Normally, reducing the mixture’s volume will increase its pressure, and introducing a spark will cause a very powerful explosion. The ability of an engine to create such explosions means a lot of energy is drawn from a small volume of fuel.

How Do You Know if Your Car Has an Interference Engine or Not?

There are three ways of knowing if your car has an interference or non-interference engine.

Reading Through Manuals

Original car manuals have detailed specifications about the make and model of the engine. The manufacturer will specify this information somewhere in the manual.

After the Belt or Chain Breaks

For an interference engine to run, perfect synchronization of belts and chains is a must. If there is a problem with the belt or chain, an interference engine will stop running, but a non-interference engine will continue operating.

But to understand how this works, let us go back to how belts, valves, crankshaft, cam gear, and pistons work. Once you ignite an interference engine, belts, the crankshaft, and cam gear start rotating. This rotation is synchronized by the belt and cam gear teeth. If the belt skips one of the teeth or accidentally breaks, the rotation of the crankshaft will be unregulated. This will cause a piston that is still moving under inertia to smash into open valves forcing the engine to stop running immediately. However much you try to restart the car, the engine won’t ignite.

Opening the Engine and Examining the Piston Movements in the Cylinder

Relying on engine failures to determine which type of engine you are using is not the best option.

1. Remove the front seats, a gas tank, and small car parts bolted on top of the engine. Though it is not a must, you may remove the subframe and air boot.
2. Once major components are out of the way, remove spark plug boots, electric cables, and clutch cable guides.
3. Unbolt the cam cover and observe how the pistons are arranged and operate. This is possible when you slowly rotate the camshaft via the kick starter.

How Do You Ensure an Interference Engine Runs for a Long Time?

Knowledge of how to maintain an interference engine is imperative. The following tips will help you when carrying out maintenance of your interference engine.

Check on the State of the Timing Belt

The timing belt in an interference engine controls the camshaft and ensures smooth operation of the engine. The belt also regulates the systematic movement of the piston and valves. If the timing belts were to break or malfunction, the engine would stop working. Unlike the non-interference engine, interference engines have limited free space. Therefore, once the belt malfunctions, the piston smashes into the valve and stops moving.

Check for signs of wear and tear and damages that jeopardize the integrity of the belt. If you notice any wear or tear on the timing belt, swiftly replace the belt.

However, to be safer, replace the timing gear after at most 60,000 miles.

Monitor the Engine Oil Level

Friction between the piston and cylinder overheats the vehicle and may cause the engine to stall. Oil does not only lubricate the engine but also dissipates excess heat. Thus always ensure the oil level is at the recommended depth, which you can check using a dipstick.

A dipstick has two marked points, and if the oil level is below the lowest marked point, you are starving the engine of oil—add more oil.

Likewise, after exposure to abnormally high-temperature oil oxidizes and turns black, losing its lubricative properties. Change the oil to improve engine performance.

Typically, engine oil is changed every 3,000 miles or three to four times a year.

Use Platinum Plugs in Place of Copper

Spark plugs are made from insulated and conductive materials to ignite the fuel/air mixture using electric current. Natural wear and tear and sooting deteriorate the plug. But the speed of deterioration is determined by the conductor’s material.

Copper spark plugs are cheap and readily available and require replacement after every 15,000 miles. On the other hand, platinum plugs easily quadruple that mileage to 60,000 miles!

Always Refer to the Manual

The internet is loaded with DIY procedures for engine checks and maintenance. Most of these tutorials are marketing oriented and advertise products that may not be compatible with an interference engine.

To avoid self-initiated problems, refer to the original manual. It has detailed explanations on how to take care of the engine, and if you can’t find one, request a pdf from the manufacturer or contact them for more help.

Change Air and Oil Filters

Dirt can enter a piston through air or oil. But with oil and air filters, debris is kept out. Change oil filters every 3,000 miles or during the replacement of the used oil. Similar to oil filters, change air filters after 90 days. But you can clean them with compressed air after a few days to remove dust particles and improve their performance.

Stick to Servicing Intervals

A car works like a human being. It feeds on fuel, runs on oil, and produces its own energy and waste. After some time, a health check-up is required.

Take your vehicle to a qualified mechanic to diagnose possible issues, and replace oil and worn-out engine parts.

How long depends on the type of service. For instance, interim servicing takes place twice a year, while full servicing takes place annually. You can go for one interim servicing and one full servicing each year.

Conclusion

There are no major differences between interference and non-interference engines other than how valves and pistons move. In the former, the piston and valves share the same space. It has a higher compression ratio and better fuel economy, and it is very efficient but at the cost of constant maintenance.

Replace the timing gear and belts after every 60,000 to 100,000 miles, failure of which will lead to catastrophic engine damages if the belt snaps.

Featured Image Credit: gan chaonan, Shutterstock