Sears Craftsman 21″ Lawn Mower Flywheel Key Replacement & Startup!- Part IV – April 3, 2014

This is a flywheel key replacement and start up again on the Sears Craftsman Craigslist find that after cleaning the carburetor it had a engine miss. Discovered that the flywheel key was partially sheared and that corrected the miss problem! Thanks to the great comments I received on this diagnosis from these channels: Alan Marshall, Lugo Small Engines, Knighthawk86855 and Brandon Marsh. See all the other 3 part series here on resurrecting the then sad looking Sears Craftsman back to a useful life again avoiding it possibly ended up in our land fields!:
Part I The Craigslist Find:
Part II Cleaning The Carburetor:
Part III First Start and Engine Miss:



16 thoughts on “Sears Craftsman 21″ Lawn Mower Flywheel Key Replacement & Startup!- Part IV – April 3, 2014

  1. Your very welcome Cliff! Yes it's unbelievable how much abuse these Briggs engines can take & still run! Seen them ran out of oil even & still keep going.

  2. my question would be,, what caused the key to shear,, meaning if you add a new one whats to stop it from happening again  in 3 minutes?

  3. Quick correction, you said that the flywheel nut is 5/16ths but it's actually 15/16ths. Our mower has the same type of engine and I just did the flywheel key replacement yesterday. 🙂

  4. I have a craftsman/briggs&stratton mower almost just like this one. I had to replace the flywheel and key because when the flywheel sheared the key the internal pressure busted the flywheel. After installing new flywheel and new blade the mower has a bad vibration. I checked the balance of the blade; perfect. Any ideas why the vibration and what might fix it?

  5. Thanks for getting back to me . You are right. I was able to get some of the bend out.After replacing the blade it seems to be running ok now.

  6. I was looking for videos on carburetor float bowl gasket problems, (mine is old and leaking), and found this video by accident. I decided to take a look at my flywheel key since I didn't know this existed.

    Sure enough it is partially sheared. It looks more like an L shape when looking at the end and part of it is cracked. I guess hitting the metal water company shut-off valve cover a few years ago did it. They installed a new pipe and it sticks up high enough that my mower blade hit it. It ruined the blade but the mower seemed to run fine after a new blade was installed. I do have a misfire about once every second though and it is kind of hard to start. It needs primed much more than the recommended 5X. Hopefully when the new key arrives I will be able to notice the misfire is gone and it will start better. I have a new carburetor float bowl gasket coming too.

    YouTube amazes me at how much we can learn here. Thank you for creating this video!

  7. hi. I have a 6.5 HP 21" craftsman and I was mowing my lawn and it just cracked banged and popped. decided to drain everything and take the crankcase apart just last night and found the issue, just one problem, i have no idea what the part is. it's like a rod that shackles/clamps to a part of the crankshaft mid way. wondering if you could help

  8. I had to fix my seras lawn mower and I had trobules to put back the fly wheel due I forget to put the handle up, now my lawn mower is working good, thanks mountain!

  9. I know you are experienced, but I have heard that if you hit the shaft with the hammer like that, that it can damage the flywheel and put invisible cracks in it that will cause the flywheel to break at some point and severely injure the operator. You can buy a universal flywheel puller on Amazon. Just be careful.

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