How to Fix a Seized Lawn Mower Engine

If you're here because you have a seized lawn mower engine and need a solution, you're in the right place.

In this guide, we'll provide clear instructions on how to fix a seized lawn mower engine and get it running again (if salvageable).

No frills, no fuss—just straightforward guidance to get the job done.

Let's get started.

How to Fix a Seized Lawn Mower Engine

Identifying the Problem

When it comes to fixing a seized lawn mower engine, the first step is confirming that the engine is indeed seized.

Understanding the common signs and symptoms of a seized engine will help you diagnose the issue accurately. Here's what to look out for:

Engine Resistance

Attempt to manually turn the engine's blade or crankshaft.

If you encounter significant resistance or the engine won't budge, it's a clear indicator of a seized engine.

Unusual Noises

Listen for any grinding or clunking noises when you attempt to start the mower.

Unusual lawn mower sounds can be a sign of internal components binding together.

Spark Plug Examination

Remove and inspect the spark plug.

If you find metal shavings or damage, it could be a result of internal engine issues.

Oil Inspection

Check the oil level and its condition.

A low oil level, the wrong type of oil, or oil that appears burnt or contaminated can contribute to engine seizures.

History of Neglect

Consider the maintenance history of the mower.

Prolonged storage without proper preparation or insufficient lubrication can lead to engine seizures.

Seized Lawn Mower Engine on Our Workbench

Required Tools and Materials

When it comes to fixing a seized lawn mower engine, having the right tools and materials on hand is crucial.

Here's what you'll need to effectively tackle this repair:


  • Socket Set: A versatile set of sockets and ratchets in various sizes will be your go-to for removing nuts and bolts.
  • Combination Wrenches: Ensure you have both standard and metric wrenches to fit different fasteners on your mower.
  • Pliers: Needle-nose and regular pliers can assist in grasping and manipulating small components.
  • Screwdrivers: You'll need both flathead and Phillips-head screwdrivers for removing screws and prying apart parts.
  • Rubber Mallet: This handy tool can be used for gentle tapping to dislodge stuck components.
  • Torque Wrench: It helps ensure you tighten bolts and nuts to the manufacturer's specifications during reassembly.
  • Brass Punch: Ideal for gently tapping without damaging metal surfaces.
  • Safety Gear: Don't forget your safety goggles and gloves to protect yourself during the repair process.


  • Engine Oil: High-quality engine oil of the right type will be needed for lubrication.
  • Penetrating Oil: A penetrating oil, such as WD-40, will help free up seized parts.
  • Replacement Parts: If you suspect damaged components, having replacements on hand is a smart move.
  • Clean Rags: Keep clean rags nearby to wipe down parts and maintain a tidy workspace.
  • Fire Extinguisher: As an extra safety measure in case of fuel-related incidents, having a fire extinguisher on hand is a wise precaution.
  • Clean Work Area: Ensure you have a well-lit and ventilated workspace with enough room to maneuver comfortably. A clutter-free work area is essential for efficiency and safety during the repair process.

Seized Lawn Mower Engine on Our Workbench Waiting for Repair

Step-by-Step Repair Process

Now that you're well-prepared with the necessary tools, materials, and safety precautions, let's delve into the step-by-step process of fixing your seized lawn mower engine.

Follow these instructions carefully to get your mower running smoothly again:

Step 1: Disconnect the Spark Plug Wire

As a safety precaution, disconnect the spark plug wire to ensure the engine cannot accidentally start during the repair.

Step 2: Confirm the Seizure

Begin by verifying that the engine is indeed seized.

Attempt to manually turn the blade or crankshaft. If there's substantial resistance or no movement at all, it's likely seized.

Step 3: Drain the Fuel Tank

Prevent potential spills or leaks during the repair by draining the fuel tank. Dispose of the fuel appropriately.

Step 4: Inspect the Engine Internals

Carefully examine the engine's internal components, focusing on the crankshaft, for signs of damage, foreign objects, or excessive wear that may have led to the seizure.

- **Bent Pushrods:** Check if any of the pushrods appear bent or damaged. Bent pushrods can cause issues with valve timing and engine operation.
- **Broken Crankshaft:** Inspect the crankshaft for any visible signs of breakage. A broken crankshaft is a severe issue that requires professional attention.
- **Broken Valves:** Examine the valves for damage or misalignment. Damaged valves can impact engine compression and performance.
- **Damaged Piston:** Look for any indications of a damaged piston, such as cracks or visible wear. A damaged piston can affect the engine's ability to generate power.

Broken Lawn Mower Piston

Step 5: Inspect for Component Destruction

Before proceeding further, inspect the engine for signs of severe damage, especially if the engine exhibited resistance during the previous steps. Look for:

  • Crankshaft Integrity: Examine the crankshaft for any visible signs of breakage or distortion.

    A broken crankshaft can lead to further component destruction and necessitate extensive repairs or engine replacement.

  • Damage to Surrounding Components: Check adjacent components such as connecting rods, piston heads, and cylinder walls for damage caused by a broken crankshaft or other catastrophic failures.

If you discover substantial component destruction or damage during this inspection, it's crucial to consider the extent of the damage and whether the engine is salvageable.

In many cases of severe damage, professional assistance and potential engine replacement may be the most viable options.

Step 6: Using Lubrication and Penetration

Apply a high-quality penetrating oil, like WD-40, to the seized parts. Allow it ample time to penetrate and loosen any stuck components.

Step 7: Applying Heat and Impact (If Necessary)

In some cases, the internal components of the engine may seize due to rust, corrosion, or excessive wear.

When this occurs, use heat and impact techniques cautiously to free these components.

Here's a closer look at what components can seize and need coaxing to free:

  • Piston Rings: Over time, piston rings can become stuck to the cylinder wall due to carbon buildup or corrosion.

    Applying gentle heat to the cylinder and using a rubber mallet to tap the piston can help break this bond.

  • Crankshaft: In rare instances, the crankshaft itself can seize due to various factors, including lack of lubrication, overheating, or excessive wear.

    A seized crankshaft typically requires professional attention, but gentle heating and tapping may sometimes help temporarily free it for diagnostic purposes.

  • Valves: Valves can seize in their guides due to deposits or corrosion. Heat can expand the metal slightly, and gentle tapping can help free them.

    However, extreme care must be taken to avoid damaging valve components.

  • Bearings: Bearings within the engine, such as main and connecting rod bearings, can seize due to inadequate lubrication or contamination.

    Heat can help expand the bearing housing, making it easier to remove or replace the damaged bearings.

  • Camshaft: The camshaft can seize in its bearings or become stuck due to corrosion.

    Applying heat and using gentle tapping techniques can help free the camshaft for inspection.

Step 8: Reassemble the Mower and Test Run (If Unseized)

After successfully freeing the seized components, cautiously reassemble the mower by following the reverse of the disassembly steps.

Reconnect the spark plug wire, and start the mower. Monitor its performance, ensuring it runs smoothly without any unusual sounds or issues.

Refer to our troubleshooting guide for help in diagnosing additional problems.

Even if you get your mower engine running again it may still have problems and/or need additional maintenance.

Step 9: Salvaging Reusable Parts (If Engine Is a Lost Cause)

Salvaged Lawn Mower Parts on Our Workbench

If your inspection reveals that the engine is beyond repair or the cost of repairs outweighs the value of the mower, you can salvage several reusable parts. Here's how:

  • Piston and Connecting Rod: Remove the piston and connecting rod assembly carefully. These components are often salvageable if undamaged.
  • Crankshaft: If the crankshaft is intact and undamaged, it can be reused in another engine or sold as a replacement part.
  • Flywheel: The flywheel is a valuable component. Remove it for reuse or resale.
  • Ignition Coil: The ignition coil can be salvaged and used in other engines.
  • Carburetor: If the carburetor is in good condition, it can be removed for use in another mower or sold.
  • Magneto: Salvage the magneto for use in future engine repairs or as a spare part.
  • Fasteners and Hardware: Collect and store nuts, bolts, screws, and other hardware in your workshop for future projects.

Properly label and store salvaged parts in a clean and dry environment.

These salvaged components can be valuable for future DIY projects or as spare parts for other small engines.

Additionally, recycling any remaining metal parts is an environmentally responsible way to dispose of the old engine.