oil pump block-off plate?

[stevet]

Is the purpose of the oil pump block-off plate just to keep water/moisture out or is it necessary to maintain gas seal in crankcase?

[crosshaven]

You will find that the blanking plate is purely to keep water and other foreign bodies out of the stator / flywheen assembly.

A piece of Duck tape would probably do if you were stuck.

Michael Kenny
Cork, Ireland