So i am new to boats, And i have some mechanic experience. I have learned that it is not enough. I have a 1984 merc blackmax 150hp. I rebuilt the unit, got it pumping water, and installed my new prop. Well when i went to shift it into foreward amd reverse. I heard a harrible grinding as it shifted. So we pull the drain plug and i get horrible milky gear oil, and on top of that metal chunks, not shavings. So im assuming o juat blew the gearcase. What i am saying is make sure you know your stuff before rebuilding, or take it to someone who does spemt 2 weeks working on this lower unit and now its all for not :,(