Why My Lawn Mower Blade Not Spinning Fast?

The grass-cutting experience can be spoiled if you realize the blades aren’t spinning as quickly as they should be. Not only would the slowly spinning blade waste your time, but it will also give your lawn an odd appearance.

There could be numerous reasons why the blades of your lawnmower are not spinning fast. Some of these include a seized pulley, a damaged deck belt, a damaged blade, a faulty safety switch, a dirty deck, or a poorly performing engine.

Read on to know more about lawn mower blade not spinning fast.

Lawn Mower Blade Not Spinning Fast

How Fast Do Mower Blades Spin?

Safety standards prohibit lawn mower blade speeds of more than 219 miles per hour. Common lawn mower blade speeds are close to 200 miles per hour.

Mower revolutions per minute (RPMs) are not governed by law, however usually operate at a rate of 2,600 to 2,900 when mowing grass. This equates to a rate of 43 to 48 revolutions per second for the typical lawnmower blade.

The American National Standards Institute (ANSI) specifies maximum allowable blade rotational velocities. Their rules state that the maximum allowable rotational speed for the blade’s tip is 19 thousand feet per minute, or around 219 miles per hour.

Lawn Mower Blade Not Spinning Fast: Reasons And Fixes

Various issues can make a lawnmower blade not to spin fast. here is a quick table of the potential causes of this problem and easy fix.

Potential CausesSolution
Damaged Belt issueReplace damaged belt
Damaged BladeRemove damaged blade
Bad safety switchFix bad safety switch
Dirty Mower DeckUse silicone spray, remove dirt from mower deck
Seized pulleyReplace the pulley

1. Damaged Belt Issue

When a belt is overstretched or worn, it might slip, preventing the blades from turning or making them turn very slowly. This occurs frequently because belts wear out and need to be replaced since they stretch.

Your lawnmower’s belt is wound around the spindle and idler pulleys, and is driven by the drive shaft pulley. If the pulley on a spindle becomes stuck due to a seized shaft, the belt will eventually break.

The Fix

  • Check deck belt and PTO belt for side wear. Check the bearings on the spindles to see if they are getting worn.
  • Lower the deck to its lowest position and remove the drive pulley belt protector to replace the belt.
  • Loosen the belt from the pulley, front deck attachment point, and PTO cable pin, then pull back to remove the spring.
  • Remove the blade spindle covers and loosen the idler pulley bolts to take the belt off between pulley and belt guard. If the belt breaks completely, ensure sure all pulleys spin freely to avoid a second break.

2. The Blade Might Be Damaged

Even while mower blades are quite durable, they can be damaged. If the blade is damaged, when engaged, the blades will not spin fast.

The Fix

Check the mower blade for any damage. To inspect the mower blade from every angle, take it off the mower. This allows you to inspect the blade from all angles and in good light, allowing you to spot even the smallest of nicks or kinks.

It is also important to check that the blade has been mounted correctly, as an improperly installed blade will slow down the cutting speed of the mower.

Related Post: 6 Reasons Why Ryobi Lawn Mower Blade Not Spinning

3. Bad Safety Switch

If the safety switch fails, the mower blades will not function. Blades will typically stop rotating or slow down considerably if any of many safety switches on a typical lawn mower are tripped.

The Fix

If your mower’s blades do not rotate or spin quickly, and you have checked out all other potential causes, check the electrical contacts in the safety switches to verify they are not being triggered unnecessarily.

These switches safeguard the operator and others around the machine, so don’t turn them off.

4. Dirty Mower Deck

The cut quality or the blade rotation speed of your lawn mower may be affected if grass accumulates underneath the deck.

Even though scraping the deck to get rid of trash may be a hassle, it’s essential if you want a clean lawn. A blocked deck can also increase the workload on your mower’s engine.

The Fix

Use a silicone spray to prevent dirt and grime from clinging to your deck. The accumulation of grass under the deck can also be reduced by avoiding mowing it when it’s rainy and by cutting it more frequently.

Related Post: Bad Boy Mower Deck Problems (Troubleshooting Guide)

5. Seized Pulley

When a pulley becomes stuck, it prevents the belt from spinning and preventing the belt from moving.

A belt can shift, start smoking, and eventually break because of this.

The Fix

  • First, with the drive belt disconnected from the engine pulley, engage the blades by lifting the lever.
  • Manually turn the spindles and pulleys, the deck lever must be engaged to disengage the brakes.
  • Make sure no pulleys are making a growling noise, and then check to see if any of them feel too snug. This indicates that the pulley needs to be replaced.

Damaged/bent lawnmower blades, a weak spring, a broken shear pin in the drive pulley, poor electrical connection or poor engine performance may also cause your lawnmower blade not to spin fast.

How Do I Make the Blade Spin Faster on My Lawnmower?

Lawn mower blade speed should never be increased. Lawn mower blade speeds are optimized for safety.

You won’t get a better cut or mow faster with a faster blade speed. Increased horsepower would speed blades through thick, heavy grass.

However, increasing blade speed stresses the blade, deck, and drive system, increasing the risk of damage. it will also cause vibration which will dislodge nuts, bolts, and the mower’s engine.

But if you determine why your mower’s blade is not spinning fast, the first step is to address the previously identified issues.

However, there are, a few methods or modification for increasing the speed of your mower’s blade depending on the type of mower.

Related Post: Is It Worth Sharpening Lawn Mower Blades?

Belt Drive Mowers and Adjustable Blade Speed

It is most straightforward to increase the blade speed of a mower with a belt drive and horizontal blades by increasing the engine speed. The blades on such mowers cease spinning whenever the engine is running since there are no gears to separate the two. Such is the case with many earlier models of walk-behind mowers.

Increasing the mower’s engine RPM will result in a faster-spinning blade on a gearless, belt-driven mower.

Adjustable Gear-Operated mower System

Geared walk-behind mowers, can have their RPM increased. A blade belt clutch (BBC) is a device that allows the engine to keep running even when the blades are stationary.

The BBC cable, located under a panel above mower deck, is used to adjust blade speed. Unscrew the BBC cable bolts and adjust it to increase RPM. To speed up or slow down blades, pull or slacken the cable.

Blade Speed Increase on Belt and Pully Mowers

Belt-and-pulley riding mowers can spin blades faster. Replace your blade pulley and drive pulley with smaller and larger ones, respectively. The mower’s cutting quality may suffer if the blades spin quicker.

How to Check Blade Speed on Your Mower?

If your mower blades seem slow, look at the grass after cutting it.

If your blades are too slow, you’ll end up tearing and damaging the grass instead of cutting it. Yet, having excessively fast blades is not only dangerous, but also inefficient.

There should be information about the engine and blade speed in the mower’s manual.

A tachometer can be used to monitor the engine speed of your lawnmower.

It’s better to have a professional mechanic take a look at your mower in cases like this because the problem is almost certainly mechanical.

Frequently Asked Questions (FAQs)

How fast should mower blades spin?

219mph (maximum).

Does Faster RPM Destroy The Engine?

If you speed up your blades in any way that is not approved, you will cause damage to your engine over time. Changes in RPM can cause issues or even invalidate a warranty if they aren’t supported by the manufacturer.

How many times a mower blade rotate per second?

43 to 48 times.

Should Lawnmower Blades Spin Freely?

As the movement of the blades on a gearless mower is entirely dependent on the operation of the engine, they should not be allowed any freedom of movement. A belt system coupled to the motor holds the blades in place.

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