R2 water pump

I have an old Marna R2 engine, (ca 1980) and the cooling water is not flowing. There is no stoppage in the intake, and water gets to the pump OK. I can not get the pump off, but can see inside a little, and I see it is a gear pump.  It does not appear to rotate when I turn the flywheel, so perhaps there is a shear pin which has failed. Do you have any pictures / manual pages that show how to get the pump off and repaired?  If there is anything online that would be best.

The pump on your R2 engine is held by 3 screws. You see only 2 of them on the outside.  The 3rd. screw is placed on the other side of the bracket holding the pump with the head of the screw  the opposite way.  You are not the first one not to find the 3rd screw. Between the camshaft, driving the pump and the pump’s driving shaft is a piece of metal (bronze) 23 m.m. x 15 m.m. with a 10m.m.hole in the middle .This metal piece is meant to break first, if the pump is frozen. We suggest that you make one yourself. The hole is not necessary, if you don’t use the boat during the wintertime. When you find the broken metal piece,you will see how it is made.

Regards Marna Motor AS.