Re: Lower Unit Cross Reference
Any V6 gearcase from 1979 on will work. The 78's & older have a barrel shape piece screwed on the top of the shift shaft. The 79's & newer are a one piece shaft that has a slight bend at the top of the shift shaft. A V6 60* gearcase shift shaft will have a different bend but you can unscrew it and use the shift shaft from your 1990 gearcase.
A V6 gearcase has a fine thread for the prop nut. A V4 gearcase has a coarse thread.
A V6 gearcase has a 4 5/8" bullet. A V4 has a 4 1/4" bullet. A V8 gearcase has a 5 1/8" bullet.
A V4 gearcase will bolt up and is usable. You'll most likely have to change props because of the gear ratio difference. If you do that be sure to use the best full synthetic gear lube available.
A V8 case will bolt up & work but again, you'll have a different gear ratio.
There is a V4 gearcase that is the size of a V6 and uses a V6 propshaft. That gearcase has a 12/27 (2.25) gear ratio. The standard V6 has a 14/26 (1.86) ratio. Than means you have to turn the driveshaft 26 times to get 14 turns from the propshaft. We can elaborate on that later if you like.
Newer V6 gearcases use a 2 piece driveshaft. The driveshaft will seem real "loose", especially with the water pump off. It's supposed to be that way.
My suggestion would be to order one from someone like right here at iboats or Superior Marine (800-338-9281) and get the right gearcase from the start.
