TOPIC: Is the Merc 80hp short shaft 4 cyl interchangeable

HI Guys, New here and glad to be part of the awesome group!
I boat a G3 and trying to find a 100hp inline 6 as they look awesome on these boats IMO. I located a 4 clay 80 hp with PT and my questions is can I swap the short shaft 80hp with the inline 6 motor? Thanks

Here’s the motor in question, im not sure of the year as I haven’t picked the unit up yet.

Ed, it appears to be a red-band "800" 80hp which places it 1968-1971. If stock, it'll have a 2.3:1 gear ratio in the lower unit.

Now what exactly are you trying to interchange? Just plopping the short-shaft 800 on the G3 in lieu of a 100hp?

Or swapping parts between the 800 and a 1000 of indeterminate year?

If you're looking at the original-style "Merc 1000", '64 and previous, for example you couldn't take that powerhead and mount it onto the 800's short-shaft lower unit. The exhaust tuner design is totally different between the later 800 and the early 1000.

IIRC you may be able to swap parts between a 1965-1970-or-so 100hp. The mid-section bolt pattern (8 bolts IIRC) is the same, with the exception that the 800 has (2) extra, smaller bolts at the rear of the tuner, that bolt to the powerhead. But either engine's powerhead and tuner plate assy should bolt right up to the short-shaft mid-section.

There may be a few slight differences in shaft design that could require a different driveshaft seal assy at the crankshaft end; but that's an easy thing to address and we can help with that when you've got the engines apart.

If that's not quite what you had in mind, pls clarify and we should be able help............ed

If your goal is to install the 1969 800 4cyl power head onto a 1965-1969 Inline-6 DSH (drive shaft housing) which includes the 1000ss, 1100ss, 950ss, 900 of that era,...You will definitely want to use the exhaust extension plate and gasket that matches the power head you decide to use.
Be sure and compare the lengths of the power head mounting studs, if the power head is going onto a different DSH, as being discussed.
doc