Lower Unit Swap: 67 Starcraft alpha 1 120hp upper: pre alpha 90hp lower

[Rod Burton]

Can I swap my lower unit out from under an alpha 1 upper: to go to a 90 hp pre alpha "lower". I have a 120 mercruiser engine. Just need a new lower. I can sen pics

 

[Bt Doctur]

if the lowers are the same and the driveshaft splines the same, then yes

 

[Rod Burton]

No Title

At a glance, They look the same but I have not taken the pre alpha lower apart yet to check the spine. What about the gear ratios?

 

[achris]

What you're calling 'pre-alpha' is infact a very old 'O' drive. (there is no such thing as a pre-alpha drive. 33 different drives fit the description as 'before the Alpha One').
It may bolt up, but the shift system is incompatible. I have looked on my Merc part drawings, and also a variety of websites. Nobody is showing breakdown drawings or listing parts for the old 'O' drives any longer. The overall ratio of the 'O' drive for the 90 was 2:1. Close to the 1.98:1 of the Alpha One, but I have no idea how the ratios are split between the housings. What I mean, is that the Alpha upper is 1.65:1 and it's lower is 1.64:1, giving the total ratio of 1.98:1. Without knowing what the tooth count in the 'O' drive lower is, no idea what the final ratio will be.

Chris.......

 

[Rod Burton]

After taking the 90hp apart, they do not match. I think I can still use the prop of the 90hp. No loss. I did get the thing for 30$.