I hit rocks with my lawn mower on accident, and now it will run for a few seconds and turn off

Pull the plug. MAKE SURE THE PLUG IS COMPLETLY REMOVED AND SEPARATED FROM THE MOWER!! Remove the cover with the pull start attached. see if you can turn it by the flywheel or the blade. If you can, you can just have the rewind repaired.
If not, then you have a probable bent or twisted crankshaft. Most likely not worth repair.

is the bolt stripped so it wont tighten?

Is the threaded hole on the Crankshaft of the mower cracked

I have the same issue, my wife hit a rock and now the mower will start for a second then quits. sucks because its brand new. I checked the oil, the gas, the spark plug, the shaft is o.k., even took it apart to check the flywheel shear pin and that's o.k. called the local mower shop and was told to go get another one! basically, the damage is internal and would cost more to fix than replace. this is done purposely by the manufactures. they don't make any money if you buy a $1.00 shear pin, new engine is much more profitable. this is coming form the repair shop.

it is common after hitting a rock for the key to shear on the flywheel to crank remove the flywheel and check it

well if you READ your owners manual its tell u how to reset it or fix it...

Hi.
Check the blade... it is bent and causes a vibration. if it is not the blade then the motor shaft is bent and that is terminal...if that happened then the mower is junk...

heatman101

Unless the blade is belt-driven, like on riding mowers, then the blade is attached directly to the engine crankshaft. Hitting a rock with a mower like this is a very common problem. You probably have a bent crankshaft. In most cases this can be repaired, but may not be worth it, considering the age of the mower. But you should call a local small engine/mower repair shop to ask for an estimate. The repair is not something you would be able to do yourself.

CK shaft it maybe bent from hitting rock.

the flywheel key is broken.take the recoil cover off.take the nut off that holds the flywheel on.thake a hammer and lightly hit the flywheel oppisit side of key way.the fly wheel will come off.replace the key.replace the flywheel.replace the recoil cover and test run the mower.should be fine.let me know if this helped................

If you hit something hard enough to partially shear the key on the blade adapter, you did shear the key on the flywheel, and it will need to be replaced for the engine to run properly.