Instructables

Mower Kicks Back--Replace the Flywheel Key

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Step 8: Install flywheel

Picture of Install flywheel
Place the flywheel on the crankshaft. It should slide down smoothly over the new key. Oil the threads on the end of the crankshaft. Place the cup, the washer, and the nut onto the crankshaft. Begin to tighten. Never pry against the flywheel cooling fins. They break easily. Turn the flywheel a couple of times to make certain it turns smoothly and nothing is obstructing it. If you did not tie back the dead man's clutch, you will hear a terrible scraping sound. Torque the flywheel nut. The recommended specifications are usually around 33 foot pounds. On some engines the figure will be 35 or 39 foot pounds. In general, if you are shearing a lot of flywheel keys for no reason, the nut is not yet tight enough.
 
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Bryan Smith3 years ago
The part of the crank shaft that the flywheel touches should be clean and dry.
I got some oil on mine and the key sheared again when I mowed over a stick. spraying on some brake cleaner got the misplaced oil out when replacing the key for the second time. I agree that the threads for the nut need oil sparingly.