Hitting an object while mowing your lawn is a common and frustrating experience. One minute you’re enjoying a perfectly striped yard, and the next, your lawn mower sputters to a halt, refusing to restart. Understanding why this happens and how to troubleshoot the problem can save you time, money, and a lot of aggravation. This article will walk you through the potential causes and solutions when your lawn mower refuses to start after an unfortunate encounter with a rock, root, or rogue garden gnome.
Immediate Assessment: What Just Happened?
The initial moments after impact are crucial. Take a deep breath and resist the urge to yank on the starter cord repeatedly. Instead, carefully consider what you hit and how the mower reacted. Did it make a loud bang? Did it simply stall quietly? The type of impact can provide clues about the potential damage.
A significant, metallic clang suggests a hard impact with a solid object, potentially causing more severe damage to the blade, crankshaft, or engine components. A quieter stall might indicate a less forceful impact, possibly involving something softer like a thick root or a hidden toy, leading to a less drastic issue like a jammed blade or a disrupted fuel line.
Knowing the nature of the object you struck can also help. Rocks and metal objects typically cause more immediate and noticeable damage, while softer objects like wood or plastic might lead to less obvious problems.
The Most Likely Culprit: The Bent Blade
A bent blade is the most frequent cause of a lawn mower failing to start after hitting an object. When a blade strikes a solid object, it can bend, warp, or even crack. This damage throws the blade off balance, creating excessive vibration that can damage the engine. More importantly, the bent blade can bind against the mower deck, preventing the engine from turning over.
Inspect the Blade Carefully: Turn off the mower and disconnect the spark plug wire to prevent accidental starting. Then, carefully inspect the blade for any signs of bending, cracking, or warping. Compare it to a new blade if possible, or at least to a mental image of how the blade should look. Look for any unevenness in the blade’s edges or any visible bends along its length.
Blade Binding: A severely bent blade may be wedged tightly against the mower deck, making it difficult or impossible to pull the starter cord. In this case, you may need to carefully try to manually rotate the blade to free it before attempting to start the engine.
Replacing or Sharpening: If the blade is only slightly bent, it may be possible to straighten it, but this is generally not recommended. Bending a blade back into shape can weaken the metal and increase the risk of it breaking during operation. The safest option is to replace the blade entirely. If the blade is not bent but simply dull, consider sharpening it. However, always ensure the blade is properly balanced after sharpening.
The Crankshaft Connection: A More Serious Problem
The crankshaft is a critical component of the lawn mower’s engine, responsible for converting the reciprocating motion of the piston into rotational motion that drives the blade. Hitting a solid object can sometimes bend the crankshaft, a much more serious problem than a bent blade.
How a Bent Crankshaft Occurs: When the blade strikes an immovable object, the sudden stop can transmit a powerful shock through the blade and up into the crankshaft. This shock can cause the crankshaft to bend, especially if the impact is severe.
Symptoms of a Bent Crankshaft: A bent crankshaft can manifest in several ways. You might experience excessive vibration, difficulty starting the engine, unusual noises during operation, or a complete inability to start the mower. In some cases, you might even notice oil leaks around the engine.
Diagnosing a Bent Crankshaft: Diagnosing a bent crankshaft can be tricky. One way to check is to remove the spark plug and try to rotate the blade manually. If you feel significant resistance or hear scraping noises, it could indicate a bent crankshaft. Another sign is if the blade wobbles noticeably as it rotates.
The Repair Dilemma: Repairing a bent crankshaft is often expensive and may not be worth it, especially on older or less expensive mowers. The labor costs involved in disassembling the engine and replacing the crankshaft can easily exceed the cost of a new mower. Consider carefully whether the repair is economically feasible before proceeding.
Fuel System Issues: From Simple to Complex
A sudden stop caused by hitting an object can sometimes disrupt the fuel system, preventing the engine from getting the fuel it needs to start.
Fuel Line Disconnection: The impact might have dislodged or disconnected a fuel line, preventing fuel from reaching the carburetor. Inspect the fuel lines running from the fuel tank to the carburetor for any signs of disconnection or damage.
Carburetor Problems: The carburetor mixes air and fuel to create a combustible mixture. The sudden jolt could have dislodged debris or caused a blockage in the carburetor, preventing it from functioning correctly. Cleaning or rebuilding the carburetor might be necessary.
Fuel Filter: A clogged fuel filter can restrict fuel flow to the engine. If the fuel filter is dirty or blocked, replace it with a new one. This is a relatively inexpensive and easy repair that can often resolve fuel-related starting problems.
Old or Stale Fuel: While not directly caused by the impact, the incident might highlight a pre-existing fuel issue. Old or stale fuel can lose its combustibility and prevent the engine from starting. Drain the old fuel and replace it with fresh fuel. Consider adding a fuel stabilizer to prevent future fuel degradation.
Spark Plug Problems: Ignition Interrupted
The spark plug ignites the air-fuel mixture in the engine cylinder, initiating the combustion process. A damaged or fouled spark plug can prevent the engine from starting.
Spark Plug Condition: Remove the spark plug and inspect it. Look for signs of fouling, such as carbon buildup, oil deposits, or a cracked insulator. Clean the spark plug with a wire brush or replace it if it is damaged.
Spark Plug Gap: The spark plug gap is the distance between the center electrode and the ground electrode. If the gap is too wide or too narrow, the spark plug may not function properly. Use a spark plug gap tool to ensure the gap is within the manufacturer’s specifications.
Spark Plug Wire: Check the spark plug wire for any signs of damage or disconnection. Ensure the wire is securely connected to both the spark plug and the ignition coil.
Testing for Spark: To test if the spark plug is producing a spark, remove the spark plug, connect it to the spark plug wire, and ground the spark plug against the engine block. Pull the starter cord. You should see a visible spark jumping across the spark plug gap. If there is no spark, the spark plug, ignition coil, or other ignition components may be faulty.
Safety Mechanisms: The Bail Arm and More
Lawn mowers are equipped with several safety mechanisms to prevent accidental starting and operation. These mechanisms can sometimes be triggered by the impact, preventing the mower from starting.
Bail Arm: The bail arm is a lever on the handle that you must hold down to start and operate the mower. If the bail arm is not fully engaged, the engine will not start. Check the bail arm and ensure it is functioning properly.
Operator Presence Control (OPC): Some lawn mowers have an operator presence control (OPC) system that shuts off the engine if you release the handle. This system may have been triggered by the impact. Check the OPC system and ensure it is functioning correctly.
Safety Switches: Lawn mowers may have other safety switches, such as a blade brake clutch (BBC) switch or a bagger switch. These switches can prevent the engine from starting if they are not properly engaged. Check all safety switches and ensure they are functioning correctly.
Low Oil Sensor: Protecting the Engine
Most modern lawn mowers are equipped with a low oil sensor that prevents the engine from starting if the oil level is too low. This is to protect the engine from damage due to lack of lubrication.
Oil Level Check: Check the oil level using the dipstick. If the oil level is below the minimum mark, add oil to bring it up to the proper level.
Sensor Malfunction: In some cases, the low oil sensor may malfunction, even if the oil level is adequate. If you suspect a faulty sensor, you can try disconnecting it temporarily to see if the mower starts. However, be aware that disabling the low oil sensor can damage the engine if the oil level is actually low.
Other Potential Problems: A Catch-All
While the above are the most common causes, other issues could be at play.
Flywheel Key: The flywheel key is a small metal piece that connects the flywheel to the crankshaft. If the mower experiences a sudden stop, the flywheel key can shear, preventing the engine from starting.
Engine Compression: Loss of engine compression can also prevent the engine from starting. This could be due to worn piston rings, damaged valves, or a blown head gasket.
Electrical Issues: While less common after an impact, electrical issues like a faulty ignition coil or a damaged wiring harness can also prevent the engine from starting.
Preventative Measures: Avoiding Future Mishaps
While accidents happen, there are several steps you can take to minimize the risk of hitting objects while mowing and damaging your lawn mower.
Clear the Lawn: Before mowing, thoroughly inspect your lawn and remove any rocks, sticks, toys, or other debris that could be struck by the mower blade.
Mowing Height: Avoid mowing too low, as this increases the risk of hitting hidden objects. Set the mower deck to a higher cutting height, especially on uneven terrain.
Be Aware: Pay attention to your surroundings while mowing. Watch out for potential hazards and avoid mowing in areas where you suspect hidden objects.
Proper Maintenance: Regularly maintain your lawn mower according to the manufacturer’s recommendations. This includes keeping the blade sharp and balanced, changing the oil, and cleaning the air filter.
By understanding the potential causes of a lawn mower failing to start after hitting an object and taking preventative measures, you can keep your mower running smoothly and your lawn looking its best. Remember to always prioritize safety when working with lawn equipment, and don’t hesitate to consult a qualified mechanic if you are unsure how to diagnose or repair a problem.
Why won’t my lawn mower start after hitting something?
The most common reason a lawn mower won’t start after hitting an object is that the object has bent the crankshaft. The crankshaft is a critical component that translates the piston’s up-and-down motion into rotational power for the blade. A sudden impact can easily warp this metal shaft, causing the engine to seize or become incredibly difficult to turn over, thus preventing it from starting.
Another possibility is that the impact has sheared the flywheel key. The flywheel key is a small, inexpensive part that aligns the flywheel with the crankshaft. Its purpose is to break under extreme stress, protecting more expensive components like the crankshaft itself. If the key is sheared, the timing will be off, preventing the engine from firing properly and resulting in a no-start condition.
Could hitting something damage the blade adapter and prevent starting?
Yes, striking a solid object can certainly damage the blade adapter, also known as the blade spindle. The blade adapter connects the blade to the engine’s crankshaft. If the impact is strong enough, it can bend, crack, or even break the adapter. A damaged blade adapter can prevent the blade from turning freely, placing undue stress on the engine and making it difficult or impossible to start.
Furthermore, a severely damaged blade adapter could cause the blade to be misaligned or even detach from the mower deck. This poses a serious safety hazard. It’s crucial to inspect the blade adapter for any signs of damage, such as cracks, bends, or wobbling, and replace it immediately if you suspect any issues.
What role does the safety brake play in this starting problem?
The safety brake, often called the blade brake, is designed to stop the blade quickly when you release the handlebar bail. After hitting an object, the mechanism controlling this brake can become dislodged or jammed. If the brake is engaged, even partially, it will prevent the engine from turning over or starting.
Inspect the blade brake cable and lever mechanism to ensure they move freely. Sometimes, debris can become lodged in the mechanism, preventing it from releasing properly. If you find any obstructions or damage to the cable or lever, clear the debris or replace the damaged components to ensure the brake releases fully.
Is there a chance the spark plug got damaged?
While less common than crankshaft damage, it is possible for a sharp impact to indirectly affect the spark plug. The jarring force can loosen the spark plug, damaging the threads in the cylinder head. If the spark plug is loose, it will not be able to create the necessary spark for ignition.
Also, depending on the object hit, debris could have been thrown into the engine compartment and damaged the spark plug wire or even the spark plug itself. Check the spark plug for any physical damage or if it’s loose. If you suspect any issues, remove and inspect the spark plug for cracks, fouling, or other signs of wear and tear, replacing it if necessary.
Could the carburetor be the problem after impact?
It’s less likely, but possible, for the carburetor to be affected by the impact. A sudden jolt could dislodge fuel lines connected to the carburetor or even damage the carburetor itself. This disruption could prevent fuel from reaching the engine, leading to a no-start situation.
Additionally, the impact might have stirred up sediment in the fuel tank, clogging the carburetor’s jets. This blockage would restrict fuel flow and prevent the engine from starting. Inspect the fuel lines for any signs of damage or disconnection and consider cleaning or rebuilding the carburetor if you suspect contamination.
How can I check if the crankshaft is bent?
The easiest way to check for a bent crankshaft is to try to rotate the blade. First, disconnect the spark plug wire for safety. Then, attempt to rotate the blade by hand. If it’s extremely difficult to turn or feels stuck, it’s a strong indication that the crankshaft is bent.
Another symptom of a bent crankshaft is a noticeable wobble in the blade when you attempt to turn it. If you observe any wobble or excessive resistance, further inspection is needed. Unfortunately, a bent crankshaft usually requires professional repair or engine replacement, as it’s a complex and specialized repair.
What if the mower just needs to be reset?
Some lawn mowers, particularly newer models, have safety features that can trigger a shutdown after a sudden impact. These safety mechanisms are designed to prevent further damage or injury. It’s possible that your mower simply needs to be reset after encountering an obstacle.
Check your owner’s manual for instructions on how to reset the mower. This may involve disengaging the blade brake, ensuring all safety switches are properly engaged, and following a specific starting sequence. Sometimes, simply turning the mower off and on again after a few minutes can resolve the issue.