Hit stump with lawn mower, engine has no compression, replaced particially sheared key, still no compression, what do i need to do? Engin is 12.5 briggs

CHECK THE OIL. If oil level gets too low, the engine may seize due to excessive friction. Check the safety interlock cable for proper operation. Check under the mower for anything that may prevent the blade from turning. If the mower hit something hard like a stump, tree root, or a large stone then check the woodruff key where the flywheel slides onto the crankshaft (there is a notch in both the flywheel and the crankshaft where this key fits). If the notches are misaligned, then the key is sheared. If the key is sheared, remove the flywheel, replace the key, reinstall the flywheel.

You may have sheared the flywheel key. This throws the timing off. If the shaft isn't bent replace the key.

Here is one suggestion,that may help. When mowing,did you hit something hard,like a root or maybe a small stump. There is a key to a key way under the fly wheel. The key has to line up with the key way for the motor,to run. This is a way that the motor is timed. This key is made to shear off if the mower hits something solid,this is to protect the motor crank shaft from damage. To get to the key,to check to see if has sheared,you must remove the fly wheel. If the key is sheared you will have to purchase a new key,any lawn mower parts store has them. If you don't have a part number,that okay,just give the model # of the motor and the horse power. The parts department can look up the key. If this is a problem,for you,than take the sheared key to the parts department,and they can match up the key,by actual seeing the key. Remember this,you must have some mechanical knowledge,when doing this repair work. The flywheel usually comes off with little effort,then again,on some fly wheels has to removed with a puller tool. I hope this helps. Sincerely,Brad Locke

sheared timing flywheel key replace it check to see if crankshft bent if throw it away or replace motor

Hi ddjklamar...

You most likely sheared the flywheel key, and that causes the flywheel to turn and not be in time to start.
Remove the flywheel and replace the key, that should solve your problem
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You will need to replace the key under the flywheel because it probably sheared when you hit the stump and you will need to replace the bent blade before starting the mower again.
I hope this helped
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may have broke crank newer mowers are not built as they use to be take out plug and place finger over hole to test for compression if none u broke more than likely the crank

I have a 12hp birggs riding mower, hit a stump, damaged shaft key, removed flywheel, replaced sheared key and I still have no compression. What do I do now?

There is a key on the flywheel. This key will shear if the blade(s) come into contact with a fixed object such as a tree stump. Check to see if this key is still intact. If it is, you probably have a broken piston rod. Hope this helps.

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.