They will often make a clicking sound as the crank goes over top dead center and any clearances are "taken up" and reversed. It is probably ok, but hey, they are so easy to take apart I recommend doing so to be sure all is well. Having had reversed the rotation should make no difference nor harm.

When swapping pistons, be sure that you verify that the ring can't get caught in the exhaust port. There is usually an arrow on the piston that should point towards the exhaust port. I might still have my 16cc piston and cylinder here if you ever need a spare.

AV8TOR