A guy at work is replacing his water pump impeller. He says that the fins on the impeller have to be bent or curved in the direction it moves to make it work right. I think that it should be put in just as it comes out of the package. Who is right???
Thanks.
Bob Van Gundy
Marine Designs,Inc.
Custom Aluminum Fabrication
803-727-4069
All of the ones I’ve replaced, although never on that engine, had to be bent in order for the impeller to seat, or fit, in the pump housing. They also must be bent in the proper direction to work right.
NOTE: I’m just a shade tree mechanic!!
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Yes, they won’t fit in the housing unless you bend them. I always turn the shaft by hand as I push the housing down over the impeller, this makes sure they bend in the right direction.
Capt. Larry Teuton
Cracker Built Custom Boats
Marine Surveying & Repair
Thanks, I stand corrected.
Bob Van Gundy
Marine Designs,Inc.
Custom Aluminum Fabrication
803-727-4069
Happy, I don’t think you needed to be corrected. The impellor arms should be straight when new. It is their pushing back toward straight that pulls/sucks water into the water pump. If they are bent when they are relaxed, they will not pump. So, you are correct. Coming out of the package, they should be straight and flexible, but, stiff.
When installed, they will necessarily be bent to fit into the water pump housing. The arms should be bent so that they sweep behind or trail the spin of the drive shaft. If put in with the arms pointing in the direction of spin, they will shortly flip back the other way. Most manuals I’ve read say it is bad to do that to them as it forces the arms to bend excessively when they flip around contributing to early failure.
2¢ from under another shade tree. 
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26’ Palmer Scott
Thanks PalmerScott. That makes me feel a little less stupid.
Bob Van Gundy
Marine Designs,Inc.
Custom Aluminum Fabrication
803-727-4069
palmer is correct
straight when out of the package, curved to fit in the housing
if you look closely at the housing, the hole is offset
that offset changes the pressure and makes teh water flow