Few things are more frustrating than pulling the cord on your lawn mower and realizing the engine is completely seized. I’ve been there—pull after pull, but the cord just won’t budge. A seized lawn mower engine can happen due to a lack of oil, overheating, or internal damage. But don’t worry—sometimes you can fix it yourself! Let’s break down the steps to get your mower back up and running.
Signs That Your Lawn Mower Engine Is Seized
Before jumping to repairs, it’s essential to confirm that the engine is truly seized. Here are some common symptoms:
- The starter rope won’t pull or is stuck.
- The engine won’t turn over even after several attempts.
- You hear a metallic clunk when trying to start.
- No response from the engine when you pull the cord or attempt to turn the crankshaft.
If your engine has seized, it means internal components, like the pistons, can’t move freely due to damage or lack of lubrication. Let’s now walk through the process of trying to fix it.
Step-by-Step Guide to Fixing a Seized Lawn Mower Engine
1. Check the Oil Level
One of the leading causes of a seized engine is running without oil or running on low oil levels. So, the first step is checking the oil.
- Remove the dipstick: Pull out the dipstick and check the oil level. If the dipstick is dry, the engine may have run out of oil.
- Inspect the oil color: If there’s oil but it’s very dark or sludgy, it could have contributed to the engine seizure.
If there’s no oil or it’s severely dirty, move on to the following steps. If your oil is fine, the issue might be internal damage.
2. Remove the Spark Plug
Before attempting to unseize the engine, make sure the lawn mower cannot accidentally start by removing the spark plug.
- Disconnect the spark plug wire: Use a socket wrench to unscrew the spark plug and set it aside.
- Removing the spark plug will release any compression in the engine, making it easier to manually rotate the crankshaft.
3. Try to Manually Rotate the Blade
Now that the spark plug is removed, it’s time to check if the engine can be unseized by manually rotating the blade. The idea is to gently break the engine free.
- Turn the mower on its side, ensuring the carburetor and air filter are facing up (to avoid leaks).
- Use a socket wrench on the center bolt of the blade (or wear gloves and carefully grab the blade) to gently try to rotate it.
If the blade moves, the engine may not be severely seized. You can try turning the blade a few times to loosen up any stuck parts.
Note: Be cautious while doing this, as the blade can be sharp!
4. Use Penetrating Oil to Loosen the Engine
If the engine is still stuck, using penetrating oil (like WD-40 or PB Blaster) can help free up seized components by lubricating and loosening rust or grime.
- Apply penetrating oil: Spray a generous amount of penetrating oil into the spark plug hole.
- Let it sit: Allow the oil to sit for several hours or even overnight to penetrate into the engine.
After letting it sit, attempt to turn the blade or the crankshaft manually again. If it starts to turn, that’s a good sign the engine is beginning to free up.
5. Check for Physical Obstructions
Sometimes a seized engine may be due to debris or an obstruction in the blade or crankshaft.
- Inspect the blade and underside of the mower for any clogs, twigs, or stones.
- Clear any debris before continuing to try and turn the crankshaft.
6. Reassemble and Add Oil
If you’ve managed to free the engine, it’s time to reassemble everything and test it.
- Replace the spark plug: Reinstall the spark plug you removed earlier.
- Fill with fresh oil: If your engine was low on oil, make sure to refill it with the recommended type and amount of oil for your lawn mower model.
- Start the engine: Once everything is reassembled, give the cord a pull to see if the engine will turn over.
7. Inspect for Internal Damage
If these steps have not worked, or if the engine seizes again after freeing it, you may have internal engine damage (like a bent crankshaft, broken piston, or damaged cylinder). At this point, it’s often best to have the engine professionally inspected.
Preventing Future Seizures
Once your mower is running smoothly again, take some steps to prevent this from happening in the future:
- Check the oil level regularly: Always check the oil before each use. Running low on oil is the number one cause of engine seizures.
- Change the oil periodically: Old, dirty oil can clog the engine and cause overheating. Change it at least once a season.
- Clean the deck and blade: Keeping the deck and blade clean prevents obstructions that could cause the engine to stall.
- Store the mower properly: Store your lawn mower in a dry, sheltered location to prevent rust and corrosion.
Conclusion
Fixing a seized lawn mower engine can sometimes be as simple as freeing stuck parts with penetrating oil, or it might involve more serious internal damage. By following these steps—checking the oil, removing the spark plug, manually rotating the blade, and using penetrating oil—you may be able to free up a locked engine without needing expensive repairs. And with proper maintenance, you can avoid future engine seizures altogether.