Saving Old Seagulls

I'm restoring a Seagull, which I believe is a 40. The engine number is SJM9648. Is there a way to test the water pump without opening the lower unit (or running the engine)? If I blow air through the copper water tube, there is no resistance. What is the impeller made of? Is it centrifugal or displacement-type?

My problem is that one of the two screws securing the lower unit is frozen, and I'd rather not resort to force if the pump actually is operational.

impellors rarely ever need replacing.
They don't pump at very low revs.
My 1942 102 has the original impellor as well as the points in the ignition which rarely need touching.

Thanks, Chris. I'm glad I don't have to open the housing.

Jay

Hello jay - the pump is centrifugal principle - the impellor is plastic - early ones were metal.
They run with quite a lot of clearance in the pump chamber, which is why you don't sense any resistance with an airline, and why Seagulls don't pump water at low revs., but do allow the motor to be run dry without any fear of the impellor getting fried.
Only thing you need to do at the bottom end is just to drain the gearboc to meake sure there is no water there, and refill with oil.

Rick