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Lawn mower makes loud clunking sound when starting: Fixes

Does your lawn mower sound like it’s on its last legs? Don’t worry; we’ve got you covered. Our guide will help you understand and fix the clunking sound issue. Let’s get your mower back in top shape.

To fix a lawn mower that makes a loud clunking sound when starting:

Remove debris buildup under the mower deck. Ensure the deck is secured, tighten loose blades, and balance. Inspect the muffler and replace it if damaged. Check the oil level and add if needed to prevent issues. Replace the worn spark plug.

Is your peaceful mowing session being interrupted by a loud clunking sound? Our guide is here to help. With easy-to-follow steps, we’ll help you fix the issue and get your mower back in top shape. Let’s roll up our sleeves and get to work!


Fixing Lawnmower Engine Clunking Sound:

Step 1: Remove Dirt from the Lawnmower Deck

With continuous usage, dirt and debris accumulate under the mower’s deck. This accumulation reduces the space for grass. Thus, the grass disturbs the blades, resulting in the production of a clunking sound. To remove the dirt, first, unplug the sparkplug wire.

This is to ensure that the engine can not unintentionally start. If your mower has a water hose attachment, you can use it to attach a hose and clean the deck. Let the mower run for a few min. You can use a strong hose if your mower does not have this and can be cleaned with water (check the manual).

Or a power washer on its lowest setting. Alternatively, you can scrape the dirt off using a scraper. And clean with a little bit of water. Once all the ground is removed, spray some silicon lubricant (like WD40) on the deck to prevent further soil accumulation under the deck.

Step 2: Check the mower deck

One of the more frequent reasons for a clunking sound is a loose sitting lawnmower deck. When the engine is starting, it makes the mower shake in a certain way that can produce a clunking sound. Turn the mower off and disconnect the spark plug cable.

This ensures that the engine can not unintentionally start when you are working on or close to the blades. Move the mower deck with your hand and check if it is loose.

– Inspecting the Nuts and Bolts of the Mower Deck

Depending on the cutting height, the mower deck can always move as it needs to go up and down. Check if there is more movement than usual. If that is the case, check the nuts and bolts that keep the mowing deck in place.

If one is loose, tighten it. It is also possible that the mowing deck will get more open over time due to wear and tear. If that is the reason, you can try to find the most affected connections and replace the bolts with slightly thicker ones.

In my two decades of experience, I’ve found that the most common reasons a lawn mower might make a loud clunking sound when starting are a loose blade, a faulty spark plug, or issues with the flywheel key. Each issue can cause distinct sounds and symptoms that are easy to identify once you know what to look for.

Step 3: Tightening the blades and make sure they are balanced

The lawnmower may also produce a clunking sound due to a partly loose blade. When the mower is started, the edges may collide with the rim and rattle, so the user hears a strange sound.

If the blades are loose, they cannot cut the grass efficiently, resulting in the bending of blades and a louder sound. You must check if all the switches are turned off and the mower has no power supply.

Preventing Accidental Mower Start

Disconnect the sparkplug cables. This prevents any accidental mower from starting when you are working on or near the blades. Tip the mower to its side and tighten up the bolt that holds the blades using a wrench. Checking if the blades are correctly balanced is also a good idea.

The only way to test this is to remove the blades. Hang them on a nail and check if the balance is ok. If not, can some heavy metal be on the side until it is correctly balanced?

Step 4: Check the Lawnmower Muffler

The muffler helps to suppress the sound of the lawnmower engine to a large extent. But if the muffler is damaged or rusted, it may not function properly.

Depending on the muffler, this can lead to a louder and clunking sound. If the muffler is damaged, it needs to be replaced. Make sure you let your mower cool down before touching it.

Using a Hammer for Muffler Inspection

Check the muffler as best as you can. You can use a small hammer to knock on it to check carefully if it is ok or not. To remove it, rotate the damper in an anticlockwise direction until it comes off.

If you do not know the correct type, use the muffler to buy a new one. Ensure it is the same size and fits perfectly on the lawnmower. Sometimes, the muffler may stick into the outlet, so you must use a wrench to remove it. Reattach the new muffler and check if it has helped.

Step 5: Check the Lawnmower Engine Oil

Engine oil enables the lawnmower engine to work smoothly. If there is low engine oil in the lawnmower, it may produce a knocking or clunking sound. Regularly check the oil level, and if needed, add some oil. Also, ensure that you use the correct oil for your mower.

If you have recently mowed the lawn, wait for it to cool down. Remove the oil fill cap and dipstick. Clean the dipstick, insert it back, and check the level with the marks on the dipstick. When the level is under the mark, add some oil.

Step 6: Check the spark plug

Sometimes, there is a misfiring from the engine. This can be due to a bad sparkplug. Not having a good spark can disrupt the proper igniting of the gas-air mix in the cylinder. As a result of this misfiring, a clunking sound can be heard.

To check, remove the sparkplug and check its condition. Clean it if it is dirty, and replace it when it looks terrible.

Step 7: Clean the filter

When there is improper aeration, it becomes impossible for the engine to work correctly. This can happen when the air filter is dirty. The dirt blocks airflow, and less air can reach the carburetor. To check and clean the air filter, remove the cover.

Remove the air filter. If you have a foam air filter, remove the more considerable dirt first. Then you can wash and dry it. If the filter is damaged, replace it. If your mower uses a paper air filter, you have no option but to replace it. After cleaning, put the filter back and close the cover.

A loose blade can cause a clunking sound as it hits against the mower deck, a faulty spark plug can cause misfires leading to loud noises, and a damaged flywheel key can cause the engine timing to be off, resulting in a clunking sound. Understanding these causes is key to diagnosing and fixing the problem.

Some Precautionary Measures:

The following are some preventive measures that should be considered:

  • Turn the engine off: While fixing any problem, ensure the power is turned off.
  • Let the engine cool: The mover should be cooled down before operating.
  • Use protection: Gloves should be worn while handling the blades or other sharp objects since.
  • Don’t overdo the WD-40: The layer of WD-40 should not be applied thickly as it drips while mowing the lawn.
  • Protect the engine: Removing the filter ensures no dirt particle enters the engine.

Frequently Asked Questions:

1. What should you do when the engine has less oil?

The engine does not function properly when there is less oil. It can produce a dull sound. The engine oil needs to be checked regularly.

Oil should be added when the level is low. A good routine would be to do this before you start mowing. Always ensure enough good quality oil to lubricate and protect the engine. Most lawnmowers can use SAE 10W-30.

2. The muffler is replaced, and the clunking sound is still heard. What to do?

There are chances that despite changing the lawnmower’s muffler, the clunking sound does not go away. This may be due to a low-quality damper used in the lawnmower that cannot suppress the noise.

One more possibility could also be that the muffler’s size in the mower is not compatible with the lawnmower’s size. In that case, it is somewhat loose.

Suppose you do not know the exact type that your machine needs. Take the worn-out damper when you buy a new one. Always go for a good quality muffler to minimize the noise level.

3. The dirt is not coming off from the lawnmower filter. What to do?

Sometimes, the dirt sticks to the filter so severely that it blocks the tiny pores in the filter. The minute pores are filled with small dust particles. It prevents airflow through the filter; thus, the engine has insufficient air to light up. If it cannot be adequately cleaned, replace it.

Fixing these issues involves different approaches. A loose blade can be tightened or replaced, a faulty spark plug can be cleaned or replaced, and a damaged flywheel key must be replaced.


Although lawnmowers, especially those with a lawn mower engine, are noisy, any unusual sound should alarm you. In that case, try to find the reason why it sounds. If your lawn mower engine knocks, it could get louder. This could get louder with more use and be particularly bad at startup.

In this blog post, we have looked at the situation when you hear a clunking sound when you start the lawnmower. It could be a loose blade that binds to the hub of the blade adapter. The blade adaptor with a bit of slack could be causing it. In most cases, it can easily be fixed.

• Importance of Regular Mower Maintenance

Always try to maintain your mower well. This decreases the chance of this kind of problem. Clean the mower after you use it. And check the oil level and blades before you start mowing.

Ensure the blade bolts are not too loose or tight on the adapter. A blade adapter seems like a crucial part that binds on the hub and holds the blade bolts.

This maintenance decreases the chance of this problem and ensures the bolts are not too loose or tight on the blade adapter. Remember, a bit of slack could be what’s causing it. So, always check these parts before you start mowing.

  1. Charlotte Simpson says:

    How to ensure the mower deck is secured properly?

    • Allard Vdhooft says:

      Thank you for reaching out, Charlotte! Follow our steps to secure the mower deck properly and fix that clunking sound issue. Let’s get your mower back to its best shape!

  2. Debra Reed says:

    This article has been incredibly helpful in diagnosing my lawnmower issue.

    • Allard Vdhooft says:

      Thank you, Debra! I’m glad the article was helpful in diagnosing your lawnmower issue. Feel free to reach out if you need further assistance. Happy mowing!

  3. Eileen Sanchez says:

    What kind of oil should I use for my lawnmower engine?

    • Allard Vdhooft says:

      Always use SAE 10W-30 oil for your lawnmower engine. It’s a common and reliable choice that will keep your engine running smoothly.

  4. Arnold Duncan says:

    Is it normal for a lawnmower to make some noise when starting?

    • Allard Vdhooft says:

      Yes, a lawnmower making noise when starting is normal. Follow our guide to identify and fix the clunking sound issue. Let’s get that mower running smoothly for you, Arnold!

  5. Andre Woods says:

    Very detailed guide on how to troubleshoot a lawnmower clunking sound.

    • Allard Vdhooft says:

      Thank you, Andre! Glad you found the guide helpful. Let’s get that lawnmower sounding great again!

  6. Dolores Chavez says:

    Should I wear ear protection when fixing my lawnmower?

    • Allard Vdhooft says:

      Don’t forget your ear protection when fixing your lawnmower. Safety always comes first!

  7. Isaiah Carlson says:

    I never realized that loose blades could cause a clunking sound on a lawnmower.

    • Allard Vdhooft says:

      Glad we could help you discover the source of the clunking sound on your lawnmower, Isaiah! Let us know if you have any other questions or concerns.

  8. Timmothy Ford says:

    How can I tell if the spark plug needs to be replaced?

    • Allard Vdhooft says:

      Hi Timmothy, if you’re hearing a clunking sound, it might be time to replace the spark plug. Check for wear and ensure it’s clean and functioning properly. Happy mowing!

  9. Stanley Webb says:

    Great tips for fixing the clunking sound issue on my lawnmower!

  10. Derrick Chavez says:

    Is it safe to clean the mower deck with water directly?

    • Allard Vdhooft says:

      Yes, it is safe to clean the mower deck with water directly. Remember to disconnect the sparkplug wire first. Follow our guide to fix the clunking sound issue and get your mower back in shape.

  11. Paula Ray says:

    The preventive measures mentioned are essential for maintaining a lawnmower.

    • Allard Vdhooft says:

      Thank you, Paula Ray! I’m glad you found the preventive measures essential. Keep an eye on your lawnmower’s maintenance for optimal performance.

  12. Martin Meyer says:

    Is there a specific way to balance the blades of the lawnmower?

    • Allard Vdhooft says:

      Thanks for your question, Martin! To balance the blades of a lawnmower, ensure they are tightened securely and check for any debris buildup under the mower deck. Happy mowing!

  13. Jacob Berry says:

    What are the signs of a damaged muffler in a lawnmower?

    • Allard Vdhooft says:

      Hey Jacob! Signs of a damaged muffler in a lawnmower include increased noise and reduced efficiency. Our guide can help you diagnose and fix the issue. Happy mowing!

  14. Alexa Holland says:

    Thank you for sharing the video links for visual assistance!

    • Allard Vdhooft says:

      Thank you, Alexa! I’m glad the video links were helpful for you. Let’s get that lawnmower back in top shape together.

  15. Alexander Hughes says:

    I will make sure to check the oil level regularly after reading this article.

    • Allard Vdhooft says:

      Thanks for reading, Alexander! Regular maintenance is key to keeping your mower in top shape. Happy mowing!

  16. Noah Barnes says:

    Can a clogged air filter cause the clunking sound?

    • Allard Vdhooft says:

      Yes, a clogged air filter can indeed cause a clunking sound in a lawn mower. Follow our guide for steps to fix the issue and get your mower running smoothly again.

  17. Lance Ferguson says:

    Great advice on how to clean the air filter of a lawnmower properly!

    • Allard Vdhooft says:

      Thank you, Lance! I’m glad you found the advice helpful. Let me know if you have any other questions or need more tips for maintaining your lawnmower.

  18. Billie Cunningham says:

    How often should I check the oil level in my lawnmower?

    • Allard Vdhooft says:

      Hey Billie! You should check the oil level in your lawnmower at least once a month to ensure it stays in top shape. Happy mowing!

  19. Mia Martin says:

    I feel more confident in fixing my lawnmower issue after reading this guide.

    • Allard Vdhooft says:

      Thank you, Mia! I’m glad the guide gave you the confidence to tackle the lawnmower issue. You’ve got this! Let me know if you need any further assistance.

  20. Minnie Ford says:

    I appreciate the step-by-step instructions provided in this article.

    • Allard Vdhooft says:

      Thank you, Minnie Ford! We’re glad you found our step-by-step instructions helpful. Let us know if you have any other questions. Happy mowing!

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