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  1. #1

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    JDgreen's Avatar
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    Bent/broken flywheel key?

    I have an '01 vintage Craftsman 6.75 hp self propelled, tried to start it two years ago and the starter rope broke, since I hade newer mowers I set it aside. Wanted to get it running this fall to bag leaves, after replacing the rope I tried to start it. It acted like the engine was trying to backfire, the rope would pull back IN toward the engine at times, it would push vapor out of the exhause but never even fired. Fuel is getting to plug, plug is working well.... It's a Briggs engine.

    Did a Google search and found several references to the same model of mower, supposedly if you hit a rock of something the flywheel key will bend or break to save the engine from damage, and with the key damaged the timing will be off far enough the engine will not start and will kick back when pull starting.

    What I find odd is, I did hit a rock hard enough a few years back that iot ruined the blade, but when I replaced the blade with a new one, the engine started right up and ran fine then. Wonder why the flywheel key problem would surface two years later?
    "I didn't plan to do anything today, but by noon I was almost half done...."

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  3. #2
    eeguns's Avatar
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    Re: Bent/broken flywheel key?

    That does seem odd that it worked fine after changing the blade. Nevertheless, the symptoms you have now do indicate the flywheel key is bent/sheared off. It's easy enough to check. Maybe when you're fixing it, the reason will present itself.
    If you do find something, I'd be curious to know what it is.
    Erik G

  4. #3

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    Re: Bent/broken flywheel key?

    Quote Originally Posted by eeguns View Post
    That does seem odd that it worked fine after changing the blade. Nevertheless, the symptoms you have now do indicate the flywheel key is bent/sheared off. It's easy enough to check. Maybe when you're fixing it, the reason will present itself.
    If you do find something, I'd be curious to know what it is.
    Will not know until spring...about 3 months away...gives me time to research the problem and get parts if needed.
    "I didn't plan to do anything today, but by noon I was almost half done...."

  5. #4

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    Re: Bent/broken flywheel key?

    The problem is surely a broken flywheel key, what might of happened is when you hit something you sheared it in half but it might of still held the timing correct, over time though it is possible the timing got thrown off. It's an easy fix and if your careful you don't have to even use a flywheel puller or knocker. Just make sure that when you put the flywheel back on you gap the coil clearance to the flywheel with a business card.

  6. #5

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    Re: Bent/broken flywheel key?

    I might add that flywheel keys are made from softer metal so that, if put under unusual stress, the key (a cheap part), will fail -- hopefully saving the flywheel and crankshaft (much more expensive parts.)
    Rocket: That's for if you wanna blow up moons.
    Gamora: No one's blowing up moons.
    Rocket: You just wanna suck the joy out of everything.

    - from the movie Guardians of the Galaxy

  7. #6

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    Re: Bent/broken flywheel key?

    I have busted and replaced mine at least 4 times. I now keep spare keys in the garage. Probably the same mower only mine says "MTD" on the side, same rated horsepower anyway.

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