Help on impellers used in Mercruiser.

 Impellers for mercruiser are only of four types.  Type one is a #1 / Alpha impeller, short blades     are called a low volume high preasure type.

These impellers are used in boats from to the 1960’s  until 1992.   They fit units called the #1 A-B-C ,  which lasted til 1972, where it was called the  #1.

 The unit starting in 1985 used the same impeller and was called the ALPHA I.    

FROM 1992 THE IMPELLER  became the longer vane ALPHA II, low preasure, high volume type impeller and these are used now.

The other impellers are the larger JABSCO type,  used on the belt driven water pumps, mounted on the front of the engines.  These two new impellers are almost the same with the difference in the hub area in the middle.  The older of these were used for years and is mounted on a 5/8” shaft with one side flat for the keyway.

Late model brass pumps have a smaller 1/2” shaft and both sides cut for the double flat hub.