Graham FisherBy Graham Fisher

Updated November 2026

A Craftsman lawn mower that won’t start after hitting something, such as a rock, stick or buried root, usually has one of a few specific problems: a damaged blade or spindle, a bent deck, a loose or cracked spark plug wire, or fuel that has been disturbed. This guide walks through the checks in the order that finds the most common faults fastest, so you can tell whether you need a quick fix or a repair shop.

Step 1: Disconnect the Spark Plug and Confirm Safety

Before you touch the blade or underside, remove the spark plug wire and tuck it away from the plug so it cannot reconnect by accident. Engage the parking brake, and if you have a riding model, make sure the mower is off and the key is removed. Mowers can start with little warning when the blade is turning, so this step matters more than any other on this list.

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Step 2: Inspect the Blade, Spindle and Deck

Tip the mower onto its side only if the manual allows it, with the air filter and carburetor facing up so oil does not reach them. Check these areas:

  • Blade: Look for bends, cracks or chipped edges. A bent blade can throw the engine out of balance and cause vibration that loosens other parts.
  • Blade bolt and washer: Confirm the bolt is tight and the blade is seated correctly with the cupped side facing the correct direction.
  • Spindle shaft: Spin the blade by hand. It should turn freely with no grinding or wobble. A bent spindle often causes the engine to bind or stall on startup.
  • Deck: Check for dents or debris wedged against the blade or drive belt.

Replace any damaged blade rather than straightening it. Manufacturers specify blades that match the deck, so use the part number listed in your owner’s manual.

Step 3: Check the Spark Plug and Wiring

Strikes can jar the spark plug wire loose or crack its boot. Reconnect the wire firmly and look for exposed wire or burns. Remove the spark plug, check the gap against the value in your manual, and look at the electrode. A wet, black or oily tip points to a fuel or air problem, while a clean but worn tip usually means the plug needs replacing. Replacing a plug is inexpensive and takes only a few minutes with a spark plug socket.

Step 4: Test the Fuel and Air Systems

A hard impact can crack the fuel line, loosen the fuel cap or knock the air filter out of position. Check each one:

  1. Inspect the fuel line for cracks, leaks or kinks.
  2. Confirm the fuel is fresh. Gasoline older than about 30 days can gum up the carburetor, and an impact can stir up sediment in the tank.
  3. Remove the air filter cover and check that the filter is seated and not torn. Clean or replace it if it is dirty.
  4. Pull the starter cord several times with the choke set correctly. If the engine coughs but will not run, the fuel system is the likely culprit.

Step 5: Look at the Drive Belt and Safety Switches

On self-propelled and riding models, an impact can knock the drive belt off its pulleys or damage a safety interlock. Make sure the belt is seated, and check that the seat switch, brake switch and blade engagement lever are not stuck or broken. Many Craftsman models will not start unless these switches are in the correct position, so a fault here can look exactly like an engine failure.

Common Mistakes

  • Starting the engine with the blade still attached after you have been working near it.
  • Straightening a bent blade instead of replacing it, which can cause imbalance and further damage.
  • Assuming the engine is ruined before checking the spark plug and fuel.
  • Tilting the mower without following the manual, which can flood the carburetor or damage the oil system.
  • Ignoring a new vibration after the impact, since it often signals a bent blade or loose hardware.
  • Spark plug socket set: A socket with a rubber insert holds the plug while you remove it, which keeps the electrode from being dropped or damaged. View on Amazon
  • Blade removal tool or breaker bar: Holding the blade still while loosening the bolt is much easier with a tool built for the job. View on Amazon
  • Replacement air filter for your model: A clean filter is a low-cost part that often restores smooth starting after a fuel or air disturbance. View on Amazon

FAQ

Can hitting a rock damage the engine itself?

Usually no. Most impacts damage the blade, deck, spark plug wire or fuel system rather than the engine block. If the engine turns over but never fires after you have checked those parts, consult a qualified small engine technician.

How do I know if the blade is bent enough to replace?

Any visible bend, crack or chipped edge means the blade should be replaced. Even a slight bend can cause vibration and uneven cutting, so do not try to hammer it straight.

Will the mower start after I replace the spark plug?

If the plug was the only fault, yes. If it still will not start, the problem is likely in the fuel, air or safety systems, which are covered in the steps above.

Conclusion

Work through the checks in order: disconnect the plug, inspect the blade and deck, test the spark plug, then look at fuel, air and safety switches. Most Craftsman no-start problems after an impact come down to a damaged blade, a loose wire or a fuel disturbance. If the mower still will not start after these steps, a small engine repair shop can diagnose the remaining fault.

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Graham Fisher

About Graham Fisher

Graham Fisher is part of our editorial team and reviews and edits our lawn mowers guides, checking product details against manufacturer specifications and owner feedback.