Two Stroke Engine - All You Need to Know

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The Indian two-wheeler market and bike insurance industry are doing very well due to the popularity that two-wheelers have garnered here. But not many bike owners are aware of the types of engines used in two-wheelers and how these differ from each other. Here, we provide you a clear understanding of these details.

What Kind of Engine is Used in Bikes?

At the heart of every two-wheeler would be a 2-stroke or a 4-stroke engine. The difference between the two have confused riders for years now. The fact that all sorts of contradictions surface around these engines only make it more difficult to understand them in detail. Each type of engine has its own fan following. So, it is necessary to look at each of these engine types in an objective manner.

In line with this, it is important to understand that the performance of a 4-stroke engine includes four main sequences, i.e, intake, compression, power, and exhaust. The crucial points of difference between a 2-stroke and a 4-stroke engine come up in each of these sequences.

• Intake - During this stroke, the piston moves down from the top of the cylinder and reduces the pressure inside it. Through the intake valve, the cylinder is filled up with a mix of air and fuel.
• Compression - During this stroke both intake and exhaust valves will be closed. The piston moves towards the top of the cylinder, compressing the mixture of air and fuel.
• Power - During the power stroke, the compressed mixture of fuel and air is ignited by a spark. The combustion moves the piston down with a huge force. This turns the crankshaft and is the main source of the power and torque output of the engine. It should be noted that the spark plug fires once every two revolutions.
• Exhaust - During this stroke, the piston moves up and pushes the burned gas out of the exhaust valve.

What Does a 2-Stroke Engine Mean?

A 2-stroke engine combines three strokes into one action. This implies that the intake and exhaust are clubbed with the piston's compression movement. This effectively eliminates the need for valves, as the inlet and exhaust ports are present on the wall of the combustion chamber.

So when the piston moves down from combustion, the exhaust gases are removed from the chamber through an exhaust port. The fuel-air mixture is drawn in through a port located at the bottom of the chamber. When the piston moves up again, the inlet and exhaust ports are blocked and the gases are compressed at the top of the chamber. The spark plug ignites the gases, and the process is repeated. The engine fires at each revolution.

Key Differences Between a 2-Stroke and a 4-Stroke Engine

1. A 2-stroke engine can generate two times the power as that generated by a 4-stroke engine of the same size. However, it also creates twice the amount of noise. The superior power generation is primarily because it fires once every revolution. Hence, it gets twice the power of a 4-stroke engine that only fires once every other revolution.
2. The 2-stroke engine also has higher weight-to-power ratio since it is lighter.
3. 2-stroke engines are substantially cheaper to manufacture and are simpler than 4-stroke engines.
4. 4-stroke engines last longer than the 2-stroke variants. However, the spark plug of the latter are more durable.
5. One of the most significant differences between the two types of engines is the fact that 4-stroke engines provide more fuel efficiency. These are also more environment-friendly in comparison to 2-stroke engines.

Do you Need Oil in a 2-Stroke Engine?

The internal combustion engine requires lubrication to function properly. So, the oil is mainly used as a lubricant in the engine. If the lubricant is not present, the friction of the moving parts will damage the engine. In a 2-stroke engine, oil is mixed with the fuel and air and this mixture is sucked into the cylinder through the inlet port.

What Kind of Oil does a 2-Stroke Engine Use?

2T engine oil is a semi-synthetic low smoke engine oil that meets the critical requirements of 2-stroke engines. It is blended from base ingredients that minimise pre-ignition, spark plug fouling, rusting, and deposit formation. 2T oil also protects the engine against seizure, wear and tear, and scuffing.

What is the Primary Cause of Pollution from a Two Stroke Engine?

Two stroke engine vehicles produce a large amount of hydrocarbons, smoke, and carbon monoxide that is dangerous to the environment. The pollution from a single two stroke engine is similar to that of 30-50 four stroke automobiles. Most of the motorcycles in the Asian countries run on two stroke engines. This pollutes the environment as much as the smog from 2.5 billion cars. Hence, the most obvious solution to the pollution problem is to get rid of the two stroke engines in small vehicles.

When the two stroke engine works, the fuel-air mixture in the cylinder gets contaminated with the lubricating oils of the engine. The contaminated mixture moves into the combustion chamber and the exhaust gases are let out through the exhaust valve. A part of the oil and fuel is mixed with the exhaust and expelled into the atmosphere. The huge clouds of oily smoke coming out from a worn-out two stroke engine is hence, primarily due to the lubricating oil used in it.

A two stroke engine is useful only in situations where the engine is not used frequently and a good power-to-weight ratio is needed.

What is the Best Two Stroke Oil?

Two stroke oil is essentially lubrication for the engine of the motorcycle. It is mixed with fuel and burns off as the bike is used. It lubricates the rings and the piston so that there is no friction with the cylinder. If oil is not used in the engine, seizing or burning of the engine is highly likely. It should be noted that oils have a film strength which indicates how it will prevent the parts of the engine from rubbing against each other. If the oil has high film strength, the protection offered is better.

The different types of two stroke oil available are as follows:

1. Petrol-based - Although petrol-based two-stroke oil does not burn very well, there are select brands that have additives in them that offer heat protection and extra lubrication.
2. Castor-based - Castor-based oil protects the inside of a two stroke engine very well. However, a castor-based premix may leave a good amount of carbon deposit on engine parts. The piston rings and power valves may also gum up, resulting in the need for more frequent maintenance procedures. The castor-based premix is more suitable for summers as well.
3. Semi-synthetic - Synthetic and castor oils are mixed together to form semi-synthetic oil. Hence, it provides optimum lubricating properties and clean burn-off. The blends may vary in the ratio of synthetic oil to castor oil. The best premix ratio is 80/20 synthetic to castor.
4. Ester-based or fully synthetic - This is the most preferred oil among motor sport riders. The fully synthetic premix consists of synthetic compounds referred to as esters. This kind of oil mixes with gas in the best possible manner, and hence, is more consistent. However, the heat protection and lubricating properties are not as good as castor-based oil. The ester-based oil is likely to leave a chalk-like residue in the exhaust port of the engine. This can be kept in check through regular maintenance.

What Fuel Should be Used in a 2 Stroke Engine?

In India, 2 stroke engines in most of the two-wheelers use petrol as fuel. Diesel engines have high compression ratio when compared to petrol engines. Hence, a diesel engine tends to be heavier than a petrol engine. This is the obvious reason for it not being used in small vehicles like motorcycles.

The diesel engine also produces more noise and vibration in comparison to a petrol engine. Small vehicles are not capable of withstanding this kind of noise and vibration. Moreover diesel engines generate more torque, but less rpm than petrol engines. In vehicles such as bikes, where the speed requirement is high, such an engine is not suitable.

How Important is the Air Filter in a Bike?

Regular maintenance of a bike involves some cumbersome tasks such as cleaning its air filter. Although this is not a job as essential as changing the oil, it is a very important part of the upkeep of your prized possession. The air filter is essentially like the gatekeeper that regulates the flow of fresh air into the engine for burning fuel. If it is not maintained well, it can choke off some air and reduce the engine power. It can also let particles into the combustion chamber and damage the engine.

How do you Clean a Bike's Air Filter?

There are three types of air filters in motorcycles:

1. Paper filters
2. Foam filters
3. Cotton filters

It is advisable to check your air filter whenever there is an oil change or after you have had a rough off-road ride. A paper filter can be replaced easily. Cotton or foam filters, on the other hand, can be cleaned, re-oiled, and assembled back into the bike if they start looking dirty. In case you do not clean the air filter as and when it is dirty, it could be damaged.

In order to clean a foam or cotton filter, it should first be removed from the housing. Once that is done, the air inlet should be blocked completely to prevent any particles from entering the engine. It is crucial to use the right kind of chemicals to clean the foam filters. If the chemical is too corrosive, it can break down the glue in the filter. If there are residues left over from the soap, the filter will not be capable of regulating the air flow in a smooth manner. Filter manufacturers offer special kits that offer you the required supplies in a single package.

1. Always wear protective gloves when cleaning the filter.
2. After taking the filter out from the housing, knock out the loose dirt.
3. Then apply the air filter cleaner and knead the filter to distribute the cleaner all over it.
4. Take care to not stretch the filter, as it can be damaged easily.
5. Wash the filter from the inside out using warm water.
6. Next, you should fill up a bucket with warm water and dissolve mild soap in it. Wash the filter in this water to get any residual dirt out. Repeat this a couple of times.
7. Gently squeeze out the water and set it aside for drying.
8. Once the filter has dried completely, ensure that the airbox is clean. Then saturate the filter with filter oil and squeeze out the excess.
9. Put it back into the housing. You may also apply some sealing grease before it is replaced in the housing.

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