Mower wont start

The flywheel key has sheared and it needs to be replaced. Replacing the flywheel key is a fairly straightforward procedure. Otherwise, it will be necessary to take the mower to have someone replace the flywheel key.

Here are some steps to follow to replace the flywheel key on your own (instructions are for a toro 20016 model mower):

1. block off the blade and driver assembly with a 2x4 to keep it from moving
2. remove the flywheel nut (regular hand force should be sufficient)
3. tap the 3 holes on the flywheel (if they aren't already threaded) using 1/4inch 20national tap set
4. remove the flywheel using a flywheel puller -- a harmonic balancer puller which matches the tecumseh bolt pattern on the flywheel also works using 3 1/4inch thread (20national, 2inch long) bolts with washers
5. NOTE: (if the blade was removed/reinstalled, tighten the blade to manufacturer's spec of 60lbs) before installing the new flywheel key
6. remove the sheared flywheel key
7. clean up the flywheel (wipe off all the dirt and grease)
8. install the new flywheel key (part 611004 for toro 20016)
9. install the flywheel (pull the bail brake handle to get the ball-brake inside the flywheel)
10. tighten the flywheel nut to manufacturer's spec of 37.5lbs
11. prime the gas bulb, give it a pull and mow away

You will need to replace an aluminum "key" in the flywheel. Whenever you hit something, the key is designed to shear so you don't break something major.