My Lawnmower Flywheel Key Is Broken

Causes of a Broken Key

• When you are using the lawnmower and hit something stationary such as a rock, cement step or the street curb, the flywheel key will sometimes break and absorb the damage, rather than the lawnmower itself. The key can also break if something gets wedged between the blade and the decking of the lawnmower.

Signs of a Broken Key

• Generally, a lawnmower will not start again if the flywheel key is broken, but it could. If you pull the starter rope to start to the lawnmower and the rope pulls back in a jerking motion so you cannot start it, it can be a broken key. Other signs that you may have a broken flywheel key could be no ignition, loss of power if the lawnmower would start or you could experience kickback and backfiring.

Diagnosing the Problem

• Before you start tearing apart the engine to replace the flywheel key, you must diagnose the problem because some of the signs of a broken key could also be the result of another problem. Check that the lawnmower has gas and spark. Also let the mower sit for about 5 to 10 minutes and try to start the mower again to rule out a flooded carburetor. Check that nothing is restraining or blocking the cutting blade from turning. After checking these possible problems with no success, you need to check the flywheel key.

Check the Flywheel Key

• Remove the bolts holding the shroud on top of the engine. You will need to remove the flywheel with a flywheel puller to reveal the crankshaft. Engine types vary between manufacturers, so you will need to follow the directions for removing the flywheel in your owner’s manual so you don’t damage the crankshaft or flywheel. The key is in a groove on the crankshaft. If the key is broken or damaged in any way, you must replace it with the same soft key. If you use a key that is not made for the specific engine, you will shear the key again or it won’t fit.