i have a 4hp 1969 evinrude wanting to replace the impeller .have taken the 4 bolts loose at the middle of lower unit but it only drops about 1/2 inch open.i have looked at some parts diagrams on line and appears to be no clip or pin holding the driveshaft at top or bottem am i missing somthing ?it is direct drive and just appears to be splined at top and bottom. THANKS for any help