Why does my flywheel key keep shearing

SOURCE: Severed Shear Pin Poulan P35TN20SE

First and foremost check to see if the crankshaft was bent when you hit the culvert. Remove the spark plug, Tilt the mower on its side at a 45 degree angle and while someone slowly pulls the starter rope see if the shaft where the blade attachs wobbles. If it does then you will need to replace the crankshaft (which can be expensive in some models). If it isn't bent, then the shroud that covers the flywheel is removed along with the other parts in that area and a flywheel "knocker" is used to remove the flywheel. At this point the old key is visible and you can see if it is sheered or not, If it is, then reverse the directions just followed after replacing the flywheel key. Chances are 99% it isn't the key, but the crankshaft.

SOURCE: I have a Craftsman LT1000

With no load, the key should NOT have sheared. These are possibilities: The replaced key was the wrong size. It should fit TIGHT with no slop at all and be long enough. A second possibility is that the keyway in either the flywheel or the shaft has been damaged. If the edges have been rolled over that would cause a new key to fail. If the flywheel had not been fully seated that would lead to failure. When re-assembling the unit fully cleaning the taper and the bore of the flywheel AND the keyway is important. A very thin lubricant is needed to insure full mating of the part. Torquing the retaining nut to the specified torque is important and this can be a bit tough. gently tapping the wheel to make sure it is seated can help. At this point disassemble and inspect the parts for damage or gauling that would prevent the taper from seating properly and dress the parts lightly with emery if the surfaces have been damaged. Make sure replacement key fits tight and is the right one.

Curtis Sewell

• 7482 Answers
• Posted on Sep 23, 2011

SOURCE: Grandson ran lawnmower on tree stump, bent blade

Hi momnpop2...

Either you can rent or if you have a puller the size to fit your flywheel then that is what you will use to pully the flywheel off after you remove the flywheel nut...
There is another way...but be really careful with this method...you can cause damage it if your overley aggressive...
Loosen the flywheel nut about 3 turns...then get two screwdrivers and put pressure on the flywheel from underneath with both screwdrivers at opposite sides of the flywheel.
Then with a brass/bronze hammer or rod strike the top of the flywheel nut as you are prying up on the flywheel with the screwdrivers...you will need some help to do it this way...
Someone to operate the screwdrivers while you hammer on the nut...the flywheel should pop up and then remove the nut and lift the flywheel.
Note: DO NOT USE A STEEL HAMMER...IT WILL DAMAGE THE NUT AND THREADS BEYOND REPAIR.
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