Our lawnmower is being vexatious. It doesn’t easily start and tends to kickback, pulling the starting cord violently from your hand. That’s not good.
According to the internets the likely cause involves a Woodruff key. You what? A Woodruff key. It’s a little metal peg that joins a shaft to something that rotates with it. It also serves as a sacrificial weak point. There’s one here just below the shaft.
That particular one attaches the flywheel to the crankshaft. The most likely issue is that sometime in the past our mower’s blade hit something hard which caused to it come to a sudden halt. The flywheel however has considerable momentum (that’s what they’re for) and it tried to keep going which caused the Woodruff key to distort and the flywheel to advance a little with respect to the crank. That’s not good, because it’s not only a flywheel. It has magnets along its edge which provide electricity for the plug. The position of these magnets with respect to the crank is crucial because therein lies the ignition timing. Advance the flywheel and the spark is produced earlier. Advance it sufficiently and the plug will fire before TDC and push the piston back from whence it came taking the cord and your hand with it.
Anyway,we’ve got an old and dead mower which has an intact key and the same B & S engine. Might do as a donor then so I started the removal process.
First, we need to take off the nut that holds flywheel to crank. There’s a special B & S tool for this as you need to hold the flywheel stationary while you loosen the nut. No, I don’t have one. The workaround is to clamp a vice grip on to the edge of the wheel which will then allow it to turn only until it comes up against the side of the block. The You Tube videos I watched were all by Americans who said things like “y’all need a seven sixteenths of a hogshead socket to get this off”. Mercifully export models are rational and a 24mm socket did the job.
Next I need to get the flywheel off the crank. B & S also do a tool for this and they helpfully cast “use wheel puller” on the wheel to encourage you to deploy it. I don’t have one, but it would screw into the two holes and haul the wheel up. That is, it would if the holes were threaded but they’re not so I’d need to tap them to whatever obscure size B & S use. No, I don’t have that tool either.
Enter these.
A large hammer and a crowbar. A large hammer is often called for if all else fails, or even before. The idea is you either hammer the flywheel up or jam the bar under it and hammer the crank down. Both of these are bad because you can crack the flywheel and a cracked wheel spinning at several thousand rpm just in front of you rarely ends well. In the event both techniques failed and the wheel remains firmly in place.
We’ve ordered a new and surprisingly cheap mower.