I had a 1954 Johnson CD-11 5.5 hp that had an almost new Sierra impeller, so when servicing the motor, I decided not to replace it. Sold the motor to an acquaintance.
The guy called me up and complained that it took him two hands to pull the motor over, so I offered to fix the problem. Just as others have stated, the Sierra pump was the problem. It was too tall and rubbing hard on the impeller plate as well as the housing.
When comparing the Sierra impeller to an OMC impeller, there was clearly more of a step-up from the brass hub to the rubber on the Sierra. I sanded the impeller on a lapping stone with 220 gr. until the rubber was nearly even with the brass hub on both top and bottom. Problem solved.
Most Sierra parts are just fine, but the impellers and points not so much.
Improvise-Adapt-Overcome
