Craftsman Mower Flywheel Key: Intact

The mower tried to eat a protruding root, emitted a horrible crash, and ran poorly until I shut it off, after which it refused to restart. Hoping against hope that the flywheel’s aluminum key had sheared, I pulled the cover, removed the starter, and found:

Mower flywheel key
Mower flywheel key

Alas, the key is in fine shape. I made the two diagonal scratches to confirm it really is aluminum.

After letting the mower sit for a day, it started and ran briefly, blatted a giant backfire that probably startled the neighborhood (because I had the exhaust aimed into the garage, which served as a wonderful resonator), died a sudden death, then made clanking sounds whenever I pulled the rope. Something is definitely broken inside, but I suspect diagnosing & fixing it will require more time and money than is justified.

I no longer form deep emotional attachments to lawn mowers, so I ordered a similar one online and the local Sears had it ready for pickup in an hour.

If I had to pull the flywheel, I’d tap the two obvious holes (one behind the shaft in the picture) and gimmick up a puller with two matching screws around a central bolt that does the heavy lifting; I can’t justify the Special Service Tool I’m sure it requires.

The old mower lasted an hour at the foot of the driveway with a “FREE – Engine probably severely broken” sign affixed to its handle; both parties got a great deal on that transaction!

9 thoughts on “Craftsman Mower Flywheel Key: Intact

  1. Just like circuitry that’s designed to sacrifice expensive semiconductors to protect the fuses.

    1. Works pretty nearly every time, too!

      Just looking at that key, though, I flat-out don’t understand how the flywheel could apply enough shear force to break the key without twisting the shaft beyond repair. Which is apparently exactly what happened…

      I wanted to autopsy the engine, but that looked more complicated than just popping the top to peek inside; I wasn’t going to build a flywheel puller just for that.

      1. Yeah, even my curiosity has its limits. Luckily, I have the remains of an old steering wheel puller that works fine as a flywheel puller. I’ve lost the weird multi-threaded bolts it came with, but to use it, I just have to find a couple of bolts with whatever threading there is on what I want to pull. As we both know, things tend to cold-weld themselves in place, so even a puller doesn’t guarantee things will go smoothly or easily. I did pick up some Kroil last time, it is as good as I remember.

        1. Kroil is good stuff, as is PB’laster (or however that’s punctuated).

          Maybe if I’d spritzed that flywheel, it would have just lifted off. Ya never know!

    2. The Lucas Electrics (Prince of Darkness) design philosophy. 30A fuse on the headlight circuit, and a 10A switch. The sheet metal cable clamps were also a nice touch… Had to replace some wire and the switch, but the fuse shrugged it off.

  2. Tapping two holes and using a puller works well but that is “the hard way.” This is the easy way…

    Remove the large nut which holds the flywheel in place, and also the large washer. Screw the large nut back onto the threaded tip of the crank, just enough to make its top surface flush with the tip of the crank. This is done to protect the threads.

    Put a large pry bar (or tire iron) under the flywheel and pry upward gently (maybe ten pounds of lift). Using a 3-pound hammer, strike the tip of the crank downward with considerable force. The flywheel pops off after 3 hits (sometimes after only one hit).

    Fast, easy, effective, no special tools, satisfaction guaranteed!

    1. Would that be rough on the ball bearings supporting the shaft?

      Or am I just a worrywart?

  3. Without the pry bar lifting the flywheel, the force of the hammer blows would be taken by the bearings.

    There is a small amount of vertical “play” in the crankshaft of the engine. The pry bar moves the crank to the highest position of this normal travel. The hammer blow suddenly moves the crank to the lowest position of the travel. Inertia (and not the pry bar) keeps the flywheel from moving whilst the crank moves 0.001 inch, breaking that tenacious taper fit. Ideally, the bearings feel little or no shock.

    There once was a K-D tool (now discontinued) called a Bingo Puller which worked in this manner. I have one and have used it many times. It is a hardened steel sleeve which fits over the crank nose to protect the threads from a mis-aimed hammer blow.

    1. Sounds good to me!

      When this mower seems ready to hop off the wheel of incarnation, I’ll give it a whack just to see what happens… [grin]

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