I can't see your video since firefox and flashplayer are currently not cooperating with each other. However, up to about 1 or 1.5 mm end float is typical of vertical Hondas I have worked on. So far it has not caused a knock. If it is actually "a few mm", it sounds as if something is wrong. End float becomes a serious problem if it is large enough to cause one side of the connecting rod to touch the side of the big-end journal.
You should inspect the Power Take-Off (engine output shaft) with the blade plate mounting boss removed, and see if you have something wound around the shaft at the lower main bearing. Also see if the center bolt holding the blade boss on the PTO is loose or a spacer is missing, allowing the boss to slide axially on the shaft.
The engine certainly shouldn't knock, but at this point I can't guess what has gone wrong.
Last edited by grumpy; 03/01/14 08:06 PM. Reason: Add detail
