Flywhee key replaced but engine still wom't turn over

HI,

I took off my flywheel and sure enough the key was sheared. So I replaced it today, but the engine still will not turn over. It's a 12 year old 18.5 HP mower.
Did I not line something else up?
Help would be appreciated.

Thanks.

:welcome:

because we only have your words to work with it is important that we are all speaking the same language about the same thing.
So firstly we need the engine make & model number and the mower model ( off the tag under the seat ).

Next,
crank = turn
fire = sparks or goes bang
start - runs for a few seconds
run - starts and continues to run.

Shumanfoo said:

HI,

I took off my flywheel and sure enough the key was sheared. So I replaced it today, but the engine still will not turn over. It's a 12 year old 18.5 HP mower.
Did I not line something else up?
Help would be appreciated.

Thanks.

Click to expand...

Did you mess with the coil? Is it set right? Checked all your safety switches? Plugs?

Shumanfoo said:

HI,

I took off my flywheel and sure enough the key was sheared. So I replaced it today, but the engine still will not turn over. It's a 12 year old 18.5 HP mower.
Did I not line something else up?
Help would be appreciated.

Thanks.

Click to expand...

This probably does not apply to your motor but I think it is still worth mentioning. One time I had a Huffy Riding mower with a 8hp motor.(?) The blade attached directly to the motor. It had a chain gear PTO on it that drove a gear box with a forward and reverse lever. The gearbox sat out on the deck it's own, fully self contained and impressive looking for sure. It looked like heavy duty industrial equipment. That mower would cut anything, small trees included. It was like riding a little bush hog. Anyway one time I broke the shear pin and after replacing it, it would not start.

I talked to a man in a mower shop and he said "Was there a thick washer on the flywheel" and I said "Yes" and he said "Did you put it back on" and I said "I think I did, maybe. I think there were two washers. I know I put one on and the nut is tight." and he told me to go home and find that big washer and put it on, and the motor will start. So that's what I did, and he was right.

I still do not see what difference that washer made. I had a washer on the flywheel and the nut was tight so I do not see how that worked. But the repairman told me "Without that washer the motor will not start" and he was sure about that being the problem, which apparently it was.

My experience has always been with a motor that size is that something else caused the flywheel key to sheer. Usually something broke inside the engine its self. 17 - 18 hp briggs with overhead cam is more and likely the connecting rod broke. I have had a couple of them where the upper part of the balancing system will freeze to the crankshaft from lack of oil. Usually an engine that sets for very long periods of time. One in particular was a man that had 2 riders and only used the one for a backup. Sometimes sat a few seasons without being used or started. Thats the one that froze up. But like above hard to say with yours. Lacking a lot of information. But bottom line is keys dont just sheer because there old. They are for alignment. The taper of the shaft and proper torque hold the flywheel in place.

Another purpose of the flywheel key is to prevent the inertia of the flywheel from twisting the end of the crankshaft off if it comes to a sudden stop caused by hitting a large root or such with the blade etc. A sudden main bearing seizure or other major failure could also cause it. A former friend sheared the flywheel key on my Troy Built Cultivator Plus on a root many years ago. He's a "former" because I had to go pickup my tiller and he failed to mentioned that it suddenly quit running when it caught the root. Took me a while to find the sheared key culprit.

Shumanfoo said:

HI,

I took off my flywheel and sure enough the key was sheared. So I replaced it today, but the engine still will not turn over. It's a 12 year old 18.5 HP mower.
Did I not line something else up?
Help would be appreciated.

Thanks.

Click to expand...

Remove the spark plus and stick something in the spark plug hole, like a pencil. Then rotate the engine (by hand). If you can feel the piston pushing the pencil out, then your rod should be fine.
If you can turn the engine over (with the key) and hold your finger over the spark plug hole, air should suck hard, and then blow your finger (or thumb) off the hole.

Air, gas, spark and compression, at the right time, is what has to happen.