Noise from lower unit after impleller change Yamaha 150 4 Stroke

[w2much]

Motor is in perfect condition just a couple of years old. Decided it was time for a new impeller. Project went easy enough. When restarting the motor noticed a knocking sound while running slowly in forward and reverse. The sound was not present in neutral nor was it present at a higher RPM. Seems to be coming from the area of the water pump. Motor was run on flushing ears to test the water pump.

 

[robert graham]

That stainless steel collar that slides own on top of pump housing is designed to take out any up and down movement of the drive shaft during operation....you need to pull up on the drive shaft while taping the collar down to effectively remove the up and down slack which can cause a knocking sound like you describe.....not all models have this collar due to certain lower unit gear designs but if yours has one then maybe drop the lower unit and snug it down....