1973 mercruiser 120/140 lower unit replacement interchange

Hello All,
I recently acquired a 1973 VIP 17' tri hull with a 120 Mercruiser (Engine S/N 3580172) (Sterndrive S/N 3645229)I/O that has been in my family for years. To my chagrin, first time out as the newest owner, i struck a submerged rock....hard. I have inspected the hull and hydraulics and all is well, but the lower casing for the outdrive is done. The tube that houses the propshaft is broken out aft of the skeg. The prop is also done. I was able to bring it back carefully under its own power. The lower unit has the rounded anti ventilation plate. I have not yet pulled it to count the splines. Where can i find a suitable replacement unit? I would prefer all new but i can rebuild if necessary. Also is there any other relevant info that i need to locate a compatible part?

Re: 1973 mercruiser 120/140 lower unit replacement interchange

Any lower unit from 1967 to 1990 is compatible with your drive. If you'd like new, have a look at SEI drives. Second hand, ebay or CL. Just be careful with second hand, sometimes they are selling problems just to be rid of them.

BTW, Welcome to iBoats.

Chris......

Re: 1973 mercruiser 120/140 lower unit replacement interchange

achris said:

Any lower unit from 1967 to 1990 is compatible with your drive. If you'd like new, have a look at SEI drives. Second hand, ebay or CL. Just be careful with second hand, sometimes they are selling problems just to be rid of them.

BTW, Welcome to iBoats.

Chris......

Click to expand...

Thank you very much. One thing i have seen online is that the pre '74 models apparently have a "short" shift throw. The site said pre 74' and post '74 are not compatible. Does that refer to internal components can not be interchanged, but the unit as a whole is compatible?

Re: 1973 mercruiser 120/140 lower unit replacement interchange

Jpcallahan said:

Thank you very much. One thing i have seen online is that the pre '74 models apparently have a "short" shift throw. The site said pre 74' and post '74 are not compatible. Does that refer to internal components can not be interchanged, but the unit as a whole is compatible?

Click to expand...

The shift plate levers are different, but the actual travel distance is the same, so the unit, as a whole, is interchangeable.

Re: 1973 mercruiser 120/140 lower unit replacement interchange

achris said:

The shift plate levers are different, but the actual travel distance is the same, so the unit, as a whole, is interchangeable.

Click to expand...

That clears that up. Many thanks for your assistance. I will post how the repairs go.
-Joe