Can a Lawn Mower Start without a Blade?

If you are troubleshooting a mower, you might be wondering if the engine will run without a blade. Maybe you want to test a new part or just curious. Well you are in the right place as this article will answer that question.

Lawn tractors and some mowers from Honda and Toro can run without blades. Other lawn mowers however, need a blade because the engine design factors in their presence. Running the engine without a blade in these instances can cause damage.

So some mowers need a blade and others do not. To be on the safe side you should check the manual or better yet, not start the engine without the blade. But if you want to know why, keep reading.

How a Lawn Mower Engine Works

Most lawn mowers use a vertical shaft engine. This engine requires a specific mass to run, and the blade is a part of that. If you remove the blade it will reduce the mass, and the engine cannot start.

As mentioned earlier, not all mowers behave like this. Some manufacturers like Honda designed their mower so that it has separate mechanisms to handle the blade. This allows the engine to function even if the blade is not installed.

The majority of lawn tractor mowers also do not need a blade to run. You can remove the blade, start the engine and the tractor will run fine. But this cannot be said for other types of lawn mowers, which is why you have to be careful.

To understand why most mowers need a blade to operate, we have to learn how their engines work. Most lawn mowers use 4-stroke engines, and this video shows how it works.

There are four parts in this cycle.

1. The piston goes into the cylinder and the intake valve is opened. This allows air and gas to get into the cylinder. The valve shuts as the piston is near the bottom.
2. The piston makes its way back up as the air and gas proceed into the combustion chamber. This movement is helped by the blade, the crankshaft and flywheel.
3. The piston reaches the top and the spark plug goes off. The explosion propels the piston into the cylinder again. If the blade is attached to the mower, it starts cutting.
4. The piston goes up again. The exhaust valve will open and release fuel. The piston gets to the top, the exhaust valve shuts and the process repeats itself.

Why Lawn Mowers Need a Blade to Run

A 4-stroke mower engine needs mass to make the piston move. The mass must be rotating and also of specific weight. It takes a lot of force to get the fuel into the combustion chamber, without which the engine cannot run. The PowerSmart 209CC works this way for instance.

In most lawn mower engines, the specifications for the rotating mass consists of the blade, flywheel and crankshaft. The combined weight of these components is enough to move the piston and get the engine to start.

If you run a lawn mower engine without the blade, the piston will not be able to complete its cycle and cause the engine to kickback.

A kickback happens when you pull the mower starter rope and the rope suddenly snaps. This can hurt or injure your hand, damage the pulley and lead to other engine issues. Doing this can break the shear key and other components in the engine. Note that if the blade is installed but not moving, the battery might not be charging.

Most lawn mowers have the blade attached to the engine. If you remove the blade the mower cannot run. You might be able to force it to start, but it can damage the engine. If the blade is not connected to the engine, you can turn and start the mower without the blade.

If you look at the manual of some lawn mower, it will state that you should never run it without the blade. This is as much about operator safety as it is about protecting the mower. You should follow this advice for your personal safety and also to ensure thee warranty is not voided.

The Risks of Running a Lawn Mower without Blades

There is the personal risk, as in kickback. There is also the risk of damaging the lawn mower itself. It all comes down to the design and the product specifications.

Even if you have a lawn tractor that can run without a blade, there is no reason to. If the blade is connected to the engine, all the more reason not to do this. With the exception of tractor mowers and riders, the flywheels on most lawn mowers are light, very light. The cost goes up with heavier flywheels so manufacturers keep the weight down.

This is where the blade comes in. When connected to the system, it serves as an extra flywheel and adds to the weight. Forcing it to run minus the blade is going to cause a lot of issues both short and long term. The blade also functions as a balance, so if you remove it, there will be a lot of vibration. This is how it works with the battery-powered EGO Power+ LM2102SP lawn mower and others.

The only possible reason why you may want to run a lawn mower without a blade is to check for damages. For example if you hit something and the blade gets bent. You might be thinking of removing the blade and turning the mower to see if the crankshaft was broken too.

You could try that, but it is possible to check the crankshaft. Try the following. You will need someone to help you here.

1. Shut the engine off.
2. Remove the spark plug wire.
3. If it is a gas mower, empty the fuel tank first.
4. Turn the mower onto its side. Have your friend pull the cord and look for signs of wobbling.

In older models you might have to take the blade off. But with new ones it will not be necessary. If the blade is bent, just turn the mower and inspect the engine. Replace the blade and try again.

Frequently Asked Questions

My mower hit something and bent the blade. Now it will not start. What should I do?

Turn the mower off. Inspect the blade. If there are cracks or bends, replace it. If the blade came loose, reinstall it. If the blade looks fine, check the engine for oil leaks or loose screws. Wait a few minutes and turn the engine on again.

If a lawn mower has a cast iron flywheel, can it run without a blade?

Cast iron flywheels are heavy and may provide the mass needed by the engine. Unfortunately, most lawn mowers discard cast iron and use aluminum for flywheels now. Aluminum is cheaper but is also lighter, which is why mowers need a blade for the extra mass.

Are all mower blades connected to the crankshaft?

No. Lawn tractor and rider engines have a separate control for the blade. With other lawn mowers the blade is connected to the crankshaft. You can check your owner’s manual for more details.

If a lawn mower tractor can run without a blade, how long can you do it?

Since the blade is not required by the engine, you can keep running it for as long as needed.

But even if a lawn tractor can do this, there is no reason why you should. If there is a problem with the mower and it cannot run, you can remove the blade after turning the engine off.

My lawn mower refuses to start. Could it have something to do with the blade?

There are many reasons why a lawn mower cannot start. It could be due to the fuel mix, engine problems, or the blade. The best approach is to turn the mower off and check the possible causes. You can start with the blade, checking for damages of any kind. If there is none, you can move on to the engine.