After putting a couple of drops of thin sewing machine oil on every few days for several weeks the flywheel nut unscrewed to reveal a sheared key. Hooray ! The keyway in the shaft is unharmed but the alloy flywheel keyway has been gouged wider a bit. I had some 4 mm keystock in the shed but the original key looks a tad bigger. Interestingly the original has a stamped B & S logo.
Being Saturday arvo and I'm out in the bush can't just wander down to a mower shop for a new B & S key so thinking might just use a bit of what's inhouse and some threadlock, but wondering if there's anything else I should be looking for when a motor hits something hard enough to shear a key. As mentioned everything else seems OK.
