Lawn Mower Doesn't Start


I have a 15 HP Craftsman riding lawn mower that uses a Briggs and Stratton engine. Anytime I put the key in and start it, all I get is a clicking sound. The flywheel doesn't turn at all and after a couple of clicks, smoke starts coming out of the engine compartment. So I talked to a guy at the Sears repair place, and he told me to change the starter, solenoid, and flywheel key. So I buy all three and put them in. (Note: The old flywheel key was in perfect condition) I give the engine full throttle and turn the key. The engine suddenly comes to life and sounds as if it had a lot more power than before. I turn the engine off and go inside.
The next day, I try to crank up the engine, and it won't start. The starter motor is turning the flywheel like is supposed to, but its just not cranking up. So I change the spark plug with a brand new one and try to crank it up again. It does nothing. I then open up the flywheel and see that the key is sheared completely in half!!! I change the key, close everything up, and restart the engine. It cranks up fine and runs perfectly. But I turn it off. Let it cool down, and crank it up again, and it won't start again. The flywheel key is again sheared in half!
So everytime I change the key, it works fine. But then the second time I crank the engine up, the key shears. What do I do? I don't think the crankshaft is bad because the original key that I pulled from the mower the first time was fine.
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The key is not meant to take the load of spinning the flywheel, it is only there to make correct alignment. Clean the inside of the flywheel taper and the outside of the spindle lightly with fine sandpaper or some such. You can even add a bit of talc, rosin, or soap stone to the taper to help it seat. Make sure you have the correct flywheel key. Make sure you set the flywheel back on the spindle with it's nut so the taper can take the load. You should reset the magneto while you have the shroud off. A business card works about right.
___________________________ Keep the whole world singing. . . . DanG

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DanG wrote:

The key is meant to take the load till something happens and the load becomes dangerous to the motor. It is supposed to break then. It is not there "only to make the correct alignment". If that were true they wouldn't make the key out of soft material. something is causing the key to be stresses in some way and you need to find out what they is. I'd run the thing for a minute and Carefully inspect the key. Ken
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I put a new key in and watched the engine run for a few minutes. I even engaged the cutting blades and drove it around a little. I didn't hear the key being sheared when I turned it off or saw any stress during the running of the mower. I think the key is being sheared when I crank it up the second time after installing the key. So I think the problem lies there, but I don't know what it is.
snipped-for-privacy@yahoo.com wrote:

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On 17 Dec 2006 11:04:04 -0800, snipped-for-privacy@gmail.com wrote:

The key *partially" shears on the first crank/run and fails on the second? Make certain the key is not moved when the flywheel is *properly seated*. You have the right key?

-- Oren
"Well, it doesn't happen all the time, but when it happens, it happens constantly."
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I've seen this on a number of occasions. In those cases the flywheel was not seating properly. If its not seated firmly on the tapered shaft, the weight of the flywheel it self attempting to keep spinning while the engine comes to a stop, will shear off the key. The taper of the shaft is what holds the load. When you are replacing the flywheel, pay particular attention to the position of the key. It is very easy to push the key down and out of the grove. If this happens the flywheel will not seat on the tapered shaft.

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I have one question. Do I put the flywheel onto the crank shaft and then push the key into the slot between the wheel and the shaft? Or do I put the key into the slot in the shaft and place the flywheel over it? Right now, I just visually align the slot in the flywheel with the slot in the shaft, set the wheel down, and then gently tap the key all the way down the slot with a small screwdriver. Could this be the problem?
Also, when I tap the key into the slot, I push it all the way down. Do I push it all the way or make the top of the key level with the top of the flywheel or the top of the crank shaft?
John Lawrence wrote:

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I set the key in the slot on the shaft, allowing it to be above the top of the shaft to help position the flywheel. Place the flywheel on the key/shaft and push or tap the key down to level with the top of the flywheel if it doesn't go to that point on it's own. It is not critical that it is flush with the top of the flywheel, but it does not need to be any deeper, certainly NOT driven to the bottom of the slot.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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On 17 Dec 2006 10:26:56 -0800, snipped-for-privacy@gmail.com wrote:

The key may be slipping a bit when you place the flywheel on. I've seen this happen. A tiny dab of bearing grease helped hold it in place enough to replace the flywheel. No more shears after that. YMMV.
-- Oren
"Well, it doesn't happen all the time, but when it happens, it happens constantly."
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This is exactly why they make hammers.
If you were in the factory you would press the flywheel on, but you are not in the factory so you use a hammer to drive the flywheel onto the shaft.
If it bottoms out before it tightens up, then you have a worn shaft/flywheel surface and you need to ship it up until it so tight that you can't pull it off without a puller.
You can buy shims at auto parts stores.
On 17 Dec 2006 10:26:56 -0800, snipped-for-privacy@gmail.com wrote:

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DONT "drive" the flywheel with a hammer. Apart from the chance of obvious damage to the flywheel itself. A hit with a hammer can alter the strength of the magnetic pick up. Factory workers do not press the flywheel on. That's why the shaft and inside of the flywheel are both tapered. The flywheel should just push to the seating position. Dont tap the key any lower than the top surface of the flywheel.
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wrong wrong wrong.
On Mon, 18 Dec 2006 15:29:53 GMT, "John Lawrence"

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Well maybe I am wrong, however I'm only speaking from my own experience. I have been repairing small engines for longer that I care to remember and I have never once, had to resort to a hammer, to replace a flywheel. Maybe I've been lucky. Also I've never had one not seat.
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Well maybe I am wrong, however I'm only speaking from my own experience. I have been repairing small engines for longer that I care to remember and I have never once, had to resort to a hammer, to replace a flywheel. Maybe I've been lucky. Also I've never had one not seat. ___________________________________________________________
I have two lawn mower / small engine shops. If I ever catch an employee using a hammer on a fly wheel, he is gone - fired.
You are RIGHT !!!!!!
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I've used a knocker to remove flywheels, but never to replace them. Am I still fired?
--

Christopher A. Young
You can\'t shout down a troll.
  Click to see the full signature.
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Still fired I'm afraid. Use a puller. An experienced Tech. can use a pry on onsite sides of the flywheel and with the end of the crank protected. tap that end. Flywheel pops off.

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Well, everyone, thanks for your help. I had tried to place the flywheel over the key onto the crankshaft (using grease to hold the key to the groove), and the same thing happened. It started, ran, then sheared. I have ordered five more keys and will try doing it a few more times. If you have any more suggestions, let me know. If not, I will try my $10 of keys, and then buy a new tractor.
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I missed part of this thread, but having worked as a mechanic for a few years I can tell you that if you have the correct key and it is installed correctly, and it shears, then something is wrong. Very wrong. Quit wasting keys - take the thing apart and find out what is wrong.
Is it shearing straight across? Or is it not getting installed straight?

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Might not be tightening the flywheel nut down enough. Might be the piston stops, but the flywheel keeps going.
--

Christopher A. Young
You can\'t shout down a troll.
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