Reed Electric

Vertical Vertigo: Hollo-Shaft Horrors

Why a little known change causes headaches.

Vertical Hollo-Shaft Motors in the 150Hp and above built on the 444 Frame size have "an issue".
Gone are the easy days when you could merely count on matching the frame size, horsepower, and speed to replace your pump drive motor.

We've come to learn (the hard way), that the premiere Vertical Hollo-Shaft manufacturer - US Motors, has made a serious change in a dimension critical to the pump head shaft (shaft that connects the motor to the pump impeller(s)).

Referring to the dimension drawing examples below, pay attention to the "CD" dimension differences between the "OLD 444 frame" and the "NEW H444 frame".

Click HERE for OLD 444 frame
Click HERE for NEW H444 frame

As you can see, there now is a dimensional difference which effects the pump head shaft. In the examples to the right, the NEW 444 frame is 2.28 inches longer in the area where the head shaft locknut threads would normally have been protruding to screw the locknut onto. Sometimes the CD dimension is shorter on the NEW style motor replacement.

Possible solutions are:

1) machine the coupling down to allow the headshaft to have enough threads exposed for the headshaft locknut
2) place a spacer plate between the pump base and the motor base
3) add washers on the locknut to allow enough threads to protrude for impeller adjustment
4) machine a new headshaft
5) machine down the locknut to get more adjustment

Just be aware and plan for the differences that the new Vertical Hollo-Shaft designs will cause when you go to adjust your impeller/pump bowl clearances via the head shaft locknut when replacing 150Hp and above.

If you need help with this issue, please call us at (800) 808-1870 or email This email address is being protected from spambots. You need JavaScript enabled to view it.

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Reed Electric - LA
5503 S. Boyle Avenue, Los Angeles, CA 90058
Ph: 323-587-2284 / Fax: 323-587-2142

Reed Electric - Reno
5375 Louie Lane, Reno, NV 89511
Phone: 775-824-7333 / Fax: 775-824-7344