How do I fix a shear-pin on my B&S mower engine?

sounds like you hit something hard and sheared the Shear pin under the Flywheel. Now your Timing is off

Shear pin. Check that you haven't broken a shear pin.

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.

Either the blade is badly out of balance/bent or it has hit something hard enough to bend the crankshaft which I have seen happen quite a few times. It could also have sheared the flywheel key causing the engine to be out of time but usually when that happens they won't even start and run.

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

The flywheel key has sheared or partially sheared which throws off the spark timing. Removing the flywheel and replacing this key will put the timing back in place. If the crankshaft bent at all you will feel a new vibration when it starts. As long as it is not to severe and the blade is not hitting any metal it is ok to run.

The vibration is caused by a bent blade and/or a bent crankshaft. The first thing to do is to replace the blade to see if the vibration goes away. If it does not then you have a bent crankshaft. The higher rpm's is not normal but is probably caused by a timing problem caused by a sheared or partially sheared flywheel key.

yes the shear pin will throw the timing off.check it anyway it might be ok but then again you ever know.check for fire coil should be at 010.from frywheel it might slip check compresstion anyway with gauge then valve gap need manual for this if ohv check pushrods this could make bad compresstion if one is bent.let me know want you find out ok

Did you possibly hit something? Sounds like the flywheel key may have sheared.