The impellers require careful removal with the purpose made Deltec tool, using any other method may put side pressure onto the head when pulling out the impeller and cause the shaft to snap. Please see the article in the link below.

How to remove a Deltec DSC1200/1700 impellor

When installing the impeller make sure the impeller locates correctly and the suction plate o-ring snaps into place. If the impeller isn’t quite located it could jump forward when started and rub the front plate.