QuestionQUESTION: I have a 3.5hp Briggs and Stratton edger that keeps shearing the woodruff key upon starting. The timing is correct and coil is mounted correctly. Flywheel is tightened correctly also. Is this suppose to be an aluminum or steel woodruff key? What would cause the key to keep shearing?
ANSWER: Is it the flywheel key or the pto key?
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QUESTION: It is the flywheel key. I have replaced it 3 or 4 times and upon start up it will shear again. The slots where the key goes on crank and flywheel look good.
AnswerThe key should be aluminum. The general things that cause a key to shear are, rust on the crankshaft taper, keys that don't fit tightly, bent or unbalanced blades, bent crankshafts and valves that stick causing backfires. I couldn't tell you just what exactly is going on without spending a good bit of time going over the engine, but those are the things I'd start with. After that, a bad flywheel and something keeping the nut from torquing down would be the next guess. Keep in mind that it's the taper of the crank and flywheel that keep the flywheel in position, like the Morse taper on a drill press. So the flywheel taper and crank taper have to fit very well.
Let me know if you have any questions. Thanks, PK.
