Morris Minor Owners Club

The engine I am rebuilding had a cast iron water pump. This has a sort of circlip betweem main body and flange for mounting pulley on and it also has a plug with a screwdriver slot in it just in front of this circlip. The impeller only sticks out of the back by 1/8". I also have a Unipart alloy one. The main problem with this one is that the impeller sticks out of the back by 1/2". I have had to grind some of the casting flash from the impeller to make this fit without catching the block internals.
Question is would the Unipart punp move more water round the engine? I also have 2 different size pulleys 3 7/8" and 4 3/4" Would fitting the larger one have any benefit?

It depends on the design of the blades. The smaller pulley would make the pump spin faster, which would increase the water flow but also sap more power.

Ian - it's normal to have to reduce the impeller on the 'new' pumps when using on old blocks. Some don't notice - and then wonder why the pump is not going round! The larger pulley was fitted to later Mini engines to cut noise and reduce power consumption. It's a common 'mod' on these Mini engines when modified to change back to the earlier smaller pulley to spin the fan faster - and so stop overheating. I would say - fit the larger pulley certainly for winter - if we get a blazing hot summer (some chance) then you can refit the smaller pulley just for that day!

What, a full day??

If v lucky!