When shifting as mentioned above, you may have to turn the driveshaft in order to help the gears line up with the shifting sleeve dogs. Always turn driveshaft clockwise looking from top. Reason? The water pump impeller fingers may get confused. I have replaced many, many impellers over the years where 1 or more fingers were facing the wrong way. This will result in inadequate water flow. I have many photos that I have taken for my customers over the years showing this condition. You can correct the fingers, if the impeller is fairly fresh it will likely not reverse fingers again, unless it is turned backwards again. Seems the quality of rubber/rubber composition has deteriorated over the years. Also engineers have reduced water pump diameters resulting in shorter fingers which are more tightly wrapped, forcing more action on the fingers as they come around to the"relaxed" side of their rotation. This coupled with poorer rubbers, ethanol contamination, and rotating the pump backwards.......is another example of today's "brilliant engineers". Newer powerhead designs have demanded higher water pressures and in some cases volumes. 10 years is often too long to ask for an impeller to last. I have the original impellers in many of my vintage OMC's. They still pump like gangbusters after 60 plus years. The impeller fingers are made of extremely high quality rubber and expertly bonded to the drive hub. The fingers are long and lazy, with a minimum of wrap or bend while passing by the pressure side of the pump chamber.
