Lower unit

[78 280zcar]

Hi, I was wondering if anybody knew if a lower unit from a merc 1969 500 50hp will fit a 1969 Merc 800 serial # 2665599. I was also wondering how you tell if you have a shortshaft or a longshaft do you measure the driveshaft because mine is 17" is mine a short shaft or a long shaft. Thanks

 

[rickdb1boat]

Re: Lower unit

Not sure about the compatability of the lower units, but I bet they would interchange. Other will confirm. As for the shaft length, it's either a 15" or 20" measured like this:<br /><br />

 

[WillyBWright]

Re: Lower unit

35Hp thru 50Hp gearcases are compatable. 650 and up gearcases are compatable (inline 4s and 6s). 60Hp thru 70Hp triples have compatable gearcases.<br /><br />So the answer is that a 500 gearcase won't fit an 850. Also, the compatability list above does not address gear ratios.<br /><br />The "shaft length" has nothing to do with shaft length. Well, it does, but it actually refers to the transom height. Generally 15", 20", 25", even 30". Your models would be either 15" or 20" like RB posted.