How do I identify a lower unit? FOLLOW UP. Got info.

[Bearcamp]

Ok the prop is brass and the only numbers I can find are AMC 381. The unit bolts to the mid section with 6 mounting bolts and 1 down from the mid section at the rear. Total of 7. The lower case separates with 9 screws and it's a 14 spline driveshaft. Also the drain for the unit gear oil is on the very bottom not like on the side of alot of them. It shifts and seems to work ok. I'm just trying to make some room and get rid of some stuff.

 

[Paul Moir]

Re: How do I identify a lower unit? FOLLOW UP. Got info.

All that matches the gearcase WillyBWright describes (50s 25hp / 30hp / 35hp, 60s 28hp / 33hp / 40hp). I just checked one from my 28hp and it has 14 splines, etc. To confirm, those gearcases should have a 1/8" drain hole on their starboard side just above the gearbox 'torpedo', and a long metal plate just above the cav plate on the port side held in place by two screws. The vent screw is on the port, and the drain screw is on the bottom front of the 'torpedo'.<br /><br />There were some minor internal differences among those gearcases, but I belive they were matched with small changes in driveshaft height. If you plan to sell it, provide a careful measurement from the lower unit seam to the top of the driveshaft.<br /><br />If your case still has the water pump attached, how many pickup tubes fit into it?<br /><br />PS - found this:<br />Michigan Wheel part AMC381<br />Dia. 10 3/4 x 11.5 pitch<br />- for 25hp-40hp pin drive OMC gearcases.<br />I don't know how accurate that info is, but if it's true than it suggests it might be from one of the lower HPs (25-30) or a higher HP used on a heavy boat.