I searched for impeller on the message board but the search came up blank. I'm a new owner, old boat (1984) with a universal M-18 inboard with Oberdorfer pump. I ordered an impeller from Torresen and while it has the same number of radial arms:
1. it is about 3/16 inch smaller in diameter and the arms barely contact the side walls of the pump housing. 2. arm thicknesses are 1/2 to 2/3 as thick as thick as the old one I'm removing 3. Overall thickness (or depth) of the impeller seems larger than the old one. Regarding items 1 and 2...Torresen has told me that, as the impeller is used, it will swell in size such that the arms will engage the side walls of the pump housing. Regarding 3...In terms of attaching the retaining ring, I will have to pull the shaft out slightly (I'm guessing maybe .02 to .03 inches) to install the retaining ring into the shaft groove. Neither of these answers seems "right" to my thinking. Has anyone else replaced the impeller on an Oberdorfer pump and encountered these problems. I suspect the part I purchased is incorrect, but Torresen is certain it is the correct one. Thanks, Ed
