Impeller problem

[Robert Fischer]

I have had to replace my impeller 2 times in the last month. I have a Universal M18 with an Oberdorfer 202M water pump. The water pump shaft is a 3/4 circle with a flat on one side which acts as a keyway. The impellers are spinning off this keyway, where the whole impeller insert is now rounded, so the shaft spins but not the impeller. This must be indicative of a larger problem with the raw water system. Please advise if posible. Thank you.

 

[Gordon Torresen]

Oberdorfer pump

I feel that your problem is confined to the pump. It would be most simple if you happened to get the wrong impeller or an aftermarket impeller without enough meat in the hub.  Take a close look at the edges of the flat on the shaft. They should be well defined. Having had two impellers spin out could have damaged the shaft.When a new impeller is installed, the outer surface should be just flush with the outer face of the pump. If it sticks out, you have the wrong impeller. I believe there is an impeller that is close in fit but it is about .040" wider. This makes that when you tighten the cover screws you are putting a bind on the impeller making it harder for the shaft to turn it. It is easy to spot if you are looking for it. Another important thing is the proper gasket. If you happened to put the cover on with silicone, instead of the gasket, you would get the same result. I hope to hear about what you find.