How to Unlock a Craftsman Push Mower

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If the motor on your Craftsman push mower is locked up, the cause could be anything from a minor problem to a ruined engine. Eliminate minor problems first by running some troubleshooting diagnostics, then check the alignment of the cutter blade arm. If it isn't damaged and one end is fractionally higher than the other, the crankshaft is bent and the engine needs to be rebuilt. If the blades are evenly spaced on both ends, the motor may have seized. Before disassembling it, try to unlock the engine; it may have few seasons of useful life left.

Things You'll Need

  • Wrench
  • Blade adapter
  • Suitable fuel container
  • Tubular spark plug wrench
  • Rope or ratcheted tie-down strap
  • Specialized penetrating oil
  • Transparent full-face shield
  • Nut driver
  • Impact wrench socket (if required)
  • Impact wrench (if required)

Troubleshooting

  • Place your hand over both the lawnmower handle and the thin pivoting operator presence control bar situated in front of the handle. Squeeze them both firmly together with your left hand to release the engine flywheel brake and pull the mower cord with your right hand. If the engine turns over, press the primer bulb on the side of the carburetor three or four times and start the engine.

  • Turn the mower on its side with the carburetor uppermost. Remove the two bolts holding the cutting blade to the blade adapter with a wrench. Inspect the blade adapter; if it is bent or damaged, replace it. Re-attach the blade and start the engine.

  • Move the mower to a hard, even surface and try starting the engine; the blade may be dragging in heavy matted grass. If the above procedures doesn't correct the problem, go to the next section.

Seized Engine

  • Tilt the mower on its side with the carburetor uppermost and place a suitable fuel container under the gas tank filler cap. Unscrew the cap and drain off the gasoline. Remove the oil filler cap and drain off the engine oil.

  • Pull the rubber plug lead boot off the spark plug. Remove the spark plug by turning it counterclockwise with a tubular plug wrench.

  • Stand the mower upright with the cylinder head uppermost, support the mower against the side of a workbench or another solid object and secure it with a length of rope or a ratcheted tie-down strap.

  • Remove the cap from a container of specialized penetrating oil formulated to free seized engines. Screw the delivery tube supplied with the oil onto the container.

  • Insert the delivery tube into the spark plug hole on top of the cylinder head. Push the tube down until you feel it bump against the top of the piston. Squeeze the container, inject 1 oz. of penetrating oil into the engine and allow the oil to soak in overnight.

  • Inject another 1-oz. of penetrating oil into the engine each morning for the following three days. Do not spill penetrating oil on a painted finish, as the additives in the oil will strip the paint right off.

  • Tie a rag around the cylinder head and over the spark plug hole to catch the penetrating oil that will blow out of the plug hole as you crank the engine. Don a transparent full-face shield to protect your eyes and face from misted penetrating oil.

  • Brace the mower with your left hand and pull firmly on the starter cord handle. If the engine turns, inject another ounce of penetrating oil into the Craftsman's engine and let it stand for 15 minutes. Pull the starter cord and turn the engine over 10 to 15 times until the starter cord offers a minimum amount of resistance.

  • Remove the rope or strap holding the mower to its support and stand the mower on its wheels. Replace the spark plug and plug lead rubber boot. Fill the engine with the correct amount of recommended engine oil, top up the gas tank, prime the carburetor and start your mower.

  • Undo the four screws holding the pull starter assembly to the engine with a nut driver if the engine remains locked. Remove the pull starter to expose the outer engine ratchet ring and the large nut that holds the engine fan to the crankshaft.

  • Attach a correctly sized impact wrench socket on the square lug on an industrial impact wrench. Place the socket on the large nut holding the engine flywheel to the crankshaft and push the impact wrench inward.

  • Squeeze the trigger and deliver a 2-second burst to the impact wrench; the impact and vibration will help the penetrating oil dislodge and separate binding oxide crystals and free up the engine. Continue delivering short bursts with the impact wrench. When the engine starts to turn, stop immediately. If the engine fails to turn after five or six bursts from the impact wrench, stop attempting to free the engine.

  • Re-attach the mower to its support in the upright position. Inject another 1/2-oz. of penetrating oil into the plug hole twice a day for another three days and repeat the freeing process with the impact wrench; this will almost certainly free up the engine, but if not, repeat the process once more until the engine turns freely in both directions.

  • Remove the rope or strap holding the Craftsman mower to its support and stand the mower on its wheels. Replace the spark plug and plug lead rubber boot. Fill the engine with the correct amount of recommended engine oil, top up the gas tank, prime the carburetor and start your mower.

Tips & Warnings

  • Most available specialized penetrating oils formulated to free seized engines carry a money-back guaranty.
  • You can rent an industrial impact wrench on a daily basis from equipment rental outlets.
  • Wear latex gloves when injecting penetrating oil into your lawnmower engine.
  • Wear eye protection and heavy gloves when using an impact wrench.

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References

  • Photo Credit Comstock Images/Comstock/Getty Images
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