Just bought a boat that i knew the engine needed rebuilding. 1974 merc 85hp. Got it rebuilt and started it without lower unit on, sounds good, slap on lower unit and has the same knocking noise i thought was in the powerhead. Guy i bought the boat from says it is a new rebuilt lower unit, and it does look like its been done over. Took the lower unit off again and tried to spin the drive shaft by hand in nuetral seems to be locked up. Was hoping to go fishing this weekend but looks like im gonna get some lower unit training.<br /> What should i be looking for when i dig into this thing? im hoping someone will tell me its an easy fix 