Hayter 48 keeps cutting out

Unless the crankshaft is made of chocolate I'd think it would take more than a whack with a mallet to bend it though. I'd be more inclined to wonder if the crankshaft really is bent. If the blades were bent you'd get a similar effect if the bend resulted in the mass not being balanced around the centre.

 

What I do is remove the blade, balance it on a round bar (a round pencil will do) and see if it sits steady (unlikely even with a good blade) then file a bit off the end of the heavy half until it is near as balanced as you can get it.