What Is Locking Up the Pulley of a Lawn Mower?

Starter Rope

• When the operator lets go of the rope, the recoil spring snaps back and the rope should recoil around the pulley. If the rope recoils improperly and comes loose or gets tangled inside the pulley or recoil spring, the rope stops pulling out. This can damage the rope, making tangles even more frequent. Remove the starter assembly cover to access the starter rope and pulley. If the rope is damaged, cut it off the pulley and replace it.

Pulley Damage

• The pulley needs to roll smoothly along the starter post, while engaging the flywheel. If the pulley gets cracked or broken, a piece may lodge against the starter cover, causing the pulley to lock-up. Pulleys can't be repaired if they are cracked or broken, so replace any pulleys that look damaged. Also check the starter post to make sure the pulley rides and spins adequately around the starter cover. Tug on the starter rope while holding the starter cover. If the pulley is still locked up, service the starter assembly.

Sheared Flywheel

• Unfortunately, the problem may lie farther into the engine's ignition system. The pulley engages the flywheel and forces it to spin around the crankshaft, and, as it spins faster, it eventually gets combustion started. If the flywheel can't spin smoothly around the crankshaft, the pulley appears to lock-up, making it difficult to pull out. Damage to the flywheel can occur if the blades hit a rock while spinning. Replace and damaged flywheels or sheared flywheel keys.

Crankshaft Damage

• Another serious problem that can cause your pulley to lock up is damage to the crankshaft or pistons. Again, if the piston and crankshaft can spin smoothly inside the engine, the pulley appears to lock-up. Damage to the crankshaft usually occurs when the bores get scoured or the seals around the crankshaft and piston lose their airtight seal. These issues may require complete disassembly of the engine. Seek professional service if you suspect damage to the crankshaft.