Good question, having never dismantled a YB I don't know the right way.
However the arrow on the top of the piston points to the front (radiator end) of the engine. And the small moon shape cutout on the bottom of the piston on one side is to the rear.

In bikes I normall see the arrow as pointing to the front, so I am assuming they are in correctly till you guys tell me otherwise

Regards
Gavan