I have replaced seveal identical pump motors over the years so I am pretty familiar with it. In replacing a 3/4 HP motor on a Hayward Super pump, when I screwed on the impeller and tightened it by hand it resulted in the motor shaft turning with high resistance, unlike previous replacemets I and made. The only difference this time was that I used a salt-water seal. I backed off on the impeller until the shaft turned with little resistance and completed the assembly. (I replaced the housing gasket properly with no problem). When I turned on the power the motor hummed but did not rotate. It occurred to me that backing off on the impeller tightening increased the length of the assembly, so I loosened by a small amount the bolts holding the assembly to the housiing. The motor immediately spun regularly but the he housing gasket leaked. If I retightened the housing bolds, the leak stopped but the motor did not rotate. When I took it apart it appears the the nose of the impeller is pushing against the end of the diffuser.
What is the silution for this.? I believe it must be related to the salt water seal. If the nose of the impeller was even 1/16 inch shorter I would have no problem.