Everything you need to Know about 4 stroke lawn mower

From this blog post, I hope to give you a good idea about the 4 stroke lawn mower.

The first ever Lawn Mover was built by Edwin Budding in 1830. Since then this grass cutting machine has evolved into several variants to fulfill various needs in mowing. Among all these variants lawn mowers with 2 stroke and 4 Stroke engines are the most famous. But due to fuel efficiency in 4 stroke lawn mower engines compared to 2 stroke ones, most countries have stopped using/producing mowers with 2 stroke engines. 

Content
1)What is a 4 stroke lawn mower and how its Engine do Process
2)4 stroke lawn mower engine oil change
3)When to Change Oil in your 4 stroke Lawn Mower
4)What fuel does a 4-stroke lawn mower use?
5)4 stroke lawn mower emission
6)Problems you may face while using 4 stroke lawn mower
    6.1)Oil Underfilling or Overfilling the engine
    6.2)4 stroke lawn mower won't start - not starting
    6.3)4 stroke lawn mower engine blows heavy white or blue smoke
    6.4)4 stroke lawn mower pull cord jerks back up hard
    6.5)4 stroke lawn mower backfire
    6.6)Frequently Asked Questions - FAQ

What is a 4 stroke lawn mower and how its Engine do Process

The 4 stroke engine in 4 stroke lawn mower requires 4 cycles(4 strokes) to complete a single combustion cycle. Each Stroke does unique functioning with regard to every single cycle. They are as follows,

1. Intake Stroke – 1st Cycle

Here, The intake valve opens and the piston-cylinder gets filled with a mixture of air and gasoline which is filtered through the carburetor. Then the valve closes As soon as the piston reaches the bottom of the cylinder.

2. Compression Stroke – 2nd cycle

Now the mixture of gasoline and air inside the cylinder is compressed to a smaller space by pushing the piston upward. By doing so the engine expects to maximize the output power when the ignition occurs.

3. Power stroke – 3rd cycle

Then the compressed mixture of air and fuel between the cylinder head and piston head is ignited. The ignition process is done by discharging a high voltage difference inside the chamber using a spark plug. As a result, the piston gets pushed downward by the Hot air that’s generated after ignition(explosion/ power stroke).

4. Exhaust Stroke – 4th cycle

This is the final function in 4 stroke cycle. As the piston comes back upward the exhaust valve gets opened. Then the spent gas is pushed out of the cylinder through the exhaust valve. As soon as the chamber becomes empty, the exhaust valve closes and again the intake valve gets open to repeat the 4 cycles again.

Here the push that gets from the power stroke is enough to keep moving the crankshaft so that to jump into the next 4 cycles.

4 stroke lawn mower engine oil change

Keeping the 4 stroke lawn mower with care and good maintenance has proven to be the best practice to secure a long-life working engine. Among the engine maintenance, the change of engine oil annually is a must. If your mower is an old one, then it has to change the oil more often than a usual new one. 

Many manufacturers recommend a change of engine oil in NEW mowers after the first five hours of use. After that best practice is to change the oil every 50 hours of use. Or it is better to do this before the start of each mowing season. 

Caution
Please carefully read the User manual that comes with the Mower before doing any maintenance.

When to Change Oil in your 4 stroke Lawn Mower

Step 1 – Place the mower on a level ground

Always check the oil levels in your 4 stroke lawn mower engine before starting to work. It is easy in that way as the engine is still in cool condition. And also make sure to keep the mower on level ground as if not, you might not get the correct oil level readings from the dipstick. 

Step 2 – Checkout the dipstick readings

Take out the dipstick and wipe it with clean clothing. Then insert it back through the fill opening and check the readings. Do this twice to get a clear understanding of the oil level inside the engine. 

By doing this you check not only the oil level but also the cleanliness of the oil as well. 

• New engine oil gives a golden or an ambient color. If the oil inside also shows clean and ambient color then you can use the machine to mow the lawn field.

• But with the time of use inside the engine, the oil color changes to darken. Here the oil becomes darker due to heat, particles that are left after burning, half-burned gas bubbles and etc. 

• It is essential to change the engine oil when it is darker. As it happens, they lose the ability to coat and protect the engine components. 

• If the engine oil is very dirty, then it’s time to change the oil. 

Step 3 – Get ready the Lawn mower to drain the oil

First of all cover your work area with newspapers, cardboard, or polythene. By doing this you can prevent spreading oil in your work area by accident. Then put a polythene cover under the lid of the gasoline tank to seal it from the inside. This will prevent leaking the gasoline/petrol when the mower is a small one, u can do this up on a workbench by covering the surface with one of the above materials. 

For large mowers, you need to use a ramp or some kind of lifting mechanism(U can use bricks to lift the 4 tires) to reach the drain plug that has situated under the mower. Then make sure to keep an oil pan under the drain plug. It will help to collect the oil that you have drained from the crankcase very easily and cleanly.

For a fast oil draining process start the engine for at least about 1 minute so that to oil get warm up. By doing so the oil will drain out smoothly and easily. 

Then Shut down the mower and remove the spark plug from the spark plug for safer practice. After that wipe and clean the area around the fill plug and drain plug area by using a rag.

Step 4 – Drain the oil

For push mowers, it is better to prop up the mower such that the spark plug faces upwards. By doing so you can prevent the leakage of gasoline through the engine. Then place the oil pan under it.

For larger mowers, lift it as I explain before and keep an oil pan under it. Then use a socket wrench to unscrew the oil drain plug. Now, You will see the hot engine oil will gradually come out. Then in the end replace the drain plug on the drain opening. And screw it until it gets fit(tight) into the tank. Do not use extra force to tighten the plug as it might damage the opening.

After collecting motor oil, put it into a disposal container and give it to a place where dispose of used oil properly. Most likely the retailer (filling station, oil change outlet, etc…) who sells motor oil is facilitated with disposing of oil as well.

Step 5 – Check whether the oil filter needs to replace

Some Lawn mowers designs are equipped with Oil filters. For those designs, you do not need to change oil frequently as in mowers without an oil filter. This option helps to filter and catch the dirt and debris. 

Normally this filter needs to be replaced once a year or according to the manufacturer’s recommendations.

You can check its condition by locating the oil filter in the mower and rotating the cartridge anti-clockwise. Often you can do this by hand.

Now carefully wipe out the oil rim as well the that gets sealed against the engine for dust particles. Then  

Step 6 – Its time to Refill the engine oil

Now, remove the oil plug and insert the tip of a funnel. Then slowly pour new engine oil into the crankcase through the funnel. By filling slowly you will avoid overflowing as the oil flows very slowly. Also, it will help you to be on alert about the oil level.

Caution 
Remember to fill the crankcase with engine oil according to the recommendations provided by the manufacturer. 

As the level of oil inside the crankcase rises please check the oil level using the dipstick. Make sure to keep the dipstick clean for every use. This will help you in getting clear readings.

Then use the filler dipstick to close and seal the fill the opening of the crankcase as it is full. Then wipe out any spilled oil around the engine as well as on the floor.

After doing all these, Connect to spark plug wire to the spark plug.

Please be very careful, when filling the oil into your Mower engine. As there are different consequences that may arise according to the level you fill the engine with oil.

Step 7 –  Now all set

Now it’s time to mow your lawn. Make sure to check the quality and level of engine oil before every time you use it. This will help you to use your 4 stroke Lawn Mower efficiently for a long time.

What fuel does a 4-stroke lawn mower use?

Both 2 stroke and 4 stroke lawn mowers rely on the same fuel type. It’s Gasoline/unleaded petrol with a rating of 88-octane or higher. But no more than 10% of ethanol in it.

4 stroke lawn mower emission

The 4 stroke engine combustion efficiency is higher Compared to 2 stroke engine. As the fuel efficiency is high in 4 stroke engine. As a result, the rate of emitting full combusted carbon (Co2) is higher in 4 cycle engine. But in 2 stroke engine, there is a high possibility to emit semi-combusted carbon (CO-carbon monoxide). And that is not good for the environment.

Problems you may face while using 4 stroke lawn mower

Below are some problems I faced when operating my $ stroke lawn mower.

Problems that may arise due to underfilling the engine

1. The engine might get overheated. As a result, the piston and the cylinder might get damaged. 
2. The engine might stuck(seize), as there is not enough oil to lubricate the parts inside. Seized engines are very hard to rebuild. Therefore most probably you will need to replace it with a new engine. Which is very costly.

Problems that may arise due to Overfilling the engine

1. The excessive oil needs to go somewhere. Therefore oil might leak to places where they are not supposed to go inside the engine. As a result, malfunctions may occur.

Because of the above reasons, it is essential to keep a proper oil level before using your Lawn Mower in the field.

4 stroke lawn mower won’t start – not starting

There might be a couple of reasons. Among them,

1. Fuel not reaching the engine – Tapping the side of the carburetor can help the flow of gas/petrol.

2. Check the spark plug in your 4 stroke lawn mower, whether it is loosened, Dirty, or Disconnected. 

• If it loosened or disconnected, plug it back and tide it up. 
• Or if is dirty, scrub and clean the coated debris layer around the needle of the spark plug and plug it back. If that does not work, then you will have to replace it with a new one.

3. Dirty air filter – by cleaning or replacing the filter you can outcome from this problem

4 stroke lawn mower engine blows heavy white or blue smoke

Below are a couple of reasons that can cause the above problem.

1. 4 stroke lawn mower Smokes heavily when the Engines parts are in bad shape

Most likely it’s because the fuel is not combusting completely inside the engine. This can happen due to,

• malfunctioning of the piston, 
• Damages in cylinders
• Gaskets break and etc…

Therefore servicing your lawn mower by a professional and replacing the broken parts will help you overcome this problem easily.

2. Use of mower inclining/tilting more than 15 degrees to the right or left. 

Because of this the oil gets leaked into the combustion chamber and gets burned. As a result, you will see blowing smoke in white, blue

3. Turned the mower upside down to do maintenance

As a result, sometimes the oil might get leaked into the ignition chamber. This can cause the white or blue smoke emission as well.

4. The use of gas (petrol) mixed with oil can cause the blowing of white or blue smoke from your lawn mower.

This is because you have used gas(petrol) mixed with oil as fuel. It is really bad for your 4 stroke lawn mower engine. Because the engine can get severe damage due to oil reaching the places where they are should not be reached.

4 stroke lawn mower pull cord jerks back up hard

Below are a couple of reasons that may be the reason to jerk back the pull cord of your 4 stroke lawn mower.

1. The blade or the impeller must be jammed with debris or rust

What you have to do is lift the mower with and lifting mechanism and check whether the blade is moveable or stuck with debris. If it is unmoveable, then clean the debris. 

You need to proceed according to the operator manual to remove the impeller cover to check the impeller condition. If it’s coated with rust or debris you can use a grinder with a metallic brush to clean them out.

2. Pull cord jammed

This can happen due to a broken spring or the coil being tangled with rope inside the recoil starter. You can easily replace this with a new full kit.

4 stroke lawn mower backfire

When the engine decelerated rapidly, sometimes you may experience a Backfire. Below are some reasons that may be the cause,

0. Lowering the engine speed rapidly
1. Carburetor damaged or the adjustments are too much lean.
2. Use of petrol (Gasoline) which contains a higher percentage of alcohol
3. Carburetor build quality problem
4. Engine having a higher temperature than normal

Frequently Asked Questions – FAQ