Lower Unit Swap Merc 900 to Merc 850

[ptarmigan61]

I have a 1965 Merc 900 inline six with a pooched power head, and a 1977 Merc 850 with a bum lower unit I might be able to get.
Do the lower units interchange? Are the gear ratios the same?
On a realted note, what other motors does the lower off the 900 fit?
Any info would be helpful.

 

[emckelvy]

Re: Lower Unit Swap Merc 900 to Merc 850

If the 90hp has a rectangular exhaust tube, coming down the center of the exhaust tower, which engages a rubber seal in the lower unit, it's the later-style and will fit the 85 hp 4-cyl motor and Inline Sixes as well. Otherwise it won't work on any of the newer motors.

The 90hp is a 2:1 and an 85 hp 4-cyl will be 2.3:1. You'd have to reduce prop pitch by 2" to account for the difference in gears.

If the older L/U is not the exhaust-tube style, it'll only fit that year Big Four and Six and older (Full Gear Shift models only).

HTH..........ed