Re: 68 650 4cyl water pump installation
The key is the new-improved design. If there is a 'flat' machined into the driveshaft for the impeller key, the flat side of the key is meant to ride there.
On older motors there is no flat, just a groove that the pin rides in. I expect they include both pin and key so they can cover more models with one kit.
I'm thinking you will have the flat and if you take a careful look, you'll likely see where the pin left wear marks in the flat. Since the key has a lot more surface area, it'll last much longer and be far less prone to wearing out and causing the impeller to slip. I've had that happen before (very badly worn driveshaft) and it's no fun hearing the Death Throes of your Beloved Merc as it goes thermonuclear!!!
Be sure to clean any rust/scale off the O.D. of the driveshaft where the impeller goes. The impeller must be free to move up & down without binding on the driveshaft, so it'll self-align. Otherwise, either the top or bottom of the impeller will wear excessively.
Check the stainless pump plate for wear, renew if it's worn or scored. Renew gaskets on both sides of the pump plate for best results.
BTW it doesn't matter which side is up on the impeller; when new the blades haven't taken a 'set'. Put a dab of waterproof marine grease (boat bearing grease works great for this) on the flat of the driveshaft and this'll hold the key nicely in place when you set the impeller down. Be sure to coat the impeller blades with a dab of liquid dish soap or grease so they aren't running dry the first time you start the motor.
Lower the upper pump cover down to the impeller. While turning the driveshaft clockwise (as seen from top), press the cover down onto the impeller. You'll get some initial resistance, just keep going and the blades will curl up and into the pump body. Seat the pump body firmly onto the water pump base and snug down the securing nuts/bolt. When you're done, turn the driveshaft to make sure you didn't accidentally 'pinch' one of the blades between pump body and base. You'll feel the resistance of the driven impeller, if it turns very freely it's likely the key fell out.
Well, that's probably more than you asked for but hopefully you'll find the info useful! HTH........ed
