[myehl1075]

I have a Craftsman Lawn Mower Model No. 917.273634 with Briggs & Stratton Engine Model 31P777. The mower will suddenly not start. I replaced battery and spark plug--no luck.

When I turn the key the flywheel spins but nothing turns over. It looks like there is a very light spark. I replaced the shear pin on the flywheel even though it was intact. Sometimes I have to "pump" the brake pedal to get the flywheel to spin--it moves slightly then spins.

Any suggestions?

[MOWERMAN2468]

If the flywheel is spinning, and the engine is not turning over, it can only be one of three things.
1. sheared flywheel key.
2. key way in flywheel stripped.
3. and the worst, the key way on the crankshaft is sheared.
I would lean toward the flywheel key being sheared. I know you are thinking, well, I already replaced the flywheel key. Well guess what, if you do not torque the flywheel nut properly, even though it seems tight, the key will shear as soon as you try and start it. Check the flywheel key visually and let me know.

[myehl1075]

if the flywheel is spinning, and the engine is not turning over, it can only be one of three things.
1. sheared flywheel key.
2. key way in flywheel stripped.
3. and the worst, the key way on the crankshaft is sheared.
i would lean toward the flywheel key being sheared. i know you are thinking, well, i already replaced the flywheel key. well guess what, if you do not torque the flywheel nut properly, even though it seems tight, the key will shear as soon as you try and start it. check the flywheel key visually and let me know.

Thanks for the response: As a follow up a couple of questions:

1. I have a torque wrench--any suggestions on how to be sure that I properly torque the flywheel nut to avoid having the key sheared?

2. If it is 2 or 3 what if any are my options?

3. Any way to check if is 2 or 3?

[MOWERMAN2468]

#2, if the keyway in the flywheel is stripped, you can replace the flywheel.
#3, if it is the keyway in the crankshaft stripped, you will have to replace the crankshaft, and this can be very costly. #2 would be bad enough, much less having to do #3.
To check and see if it is 2, or 3, you will have to remove the flywheel and visually inspect.