I'm new to the forum, here because my Honda HRX217 lawn mower just had the blade impact a short stump along the lot line which caused it to stop immediately. This model has the blade brake/clutch. When restarting it, it vibrated a lot. Checked the dual blades, and one end of the bottom blade was bent pretty significantly. Removed both blades and restarted it. Still vibrated a lot. Didn't want to idle well either. Given it was the end of the lawn season, a drained the fuel and ran the engine until it stopped. Unlike previous years, the engine started slowing down then accelerating frequently as the fuel ran out, and a couple of times backfired. Never did that before, especially the back fire.
So here's my question - is it possible the vibration is not caused by a bent crankshaft (I did not feel any unusual drag when pulling the starter rope slowly), but the impact and instantaneous stopped caused the flywheel key to break, and given the flywheel inertia, caused the flywheel magnets (for the ignition timing pickup) to advance enough so that it would still run, but is causing pre-ignition and causing the vibration, and the backfire and poor idle speed control? Or is it likely I have both (flywheel key broken with advanced timing now, plus a slightly bent crankshaft)?
I was going to put it away for the winter, but was going to buy a new crank, oil seals, and FIPG (form-in-place-gasket) sealant with intent to change the crankshaft out, but now thinking about the very unsmooth idle and the backfire a couple of times when running the fuel out that I may have another cause not requiring a crankshaft replacement and need to replace oil seals.
Any thoughts on this?