[MBS1030]

I have an 850 mercury with a bad lower. I also have a 650 with a bad head. I've disassembled both lowers and noticed some differences. The 850 drive shaft has pin at the top and the 650 doesn't. The water pump for the 650 has a smaller diameter base than the 850. The gears are also different. Can I make it work? Which gears should I use. The prop shaft clutch assemblies are different also. One more thing, the drive shafts accept the bearings differently. The 850 uses a race and bearing. Thanks for any help.

[ledgefinder]

I think you'll find that the one without the pin is too long, that is the driveshaft is too long. If not, & if everything else bolts up, you may be good to go. The pin is a spring-loaded preload for the driveshaft bearings in the lower unit (under the waterpump). The lower unit without the pin is the older design, and has the right bearing setup to not need the preload. In my vast experience (tried it once), the non-pin one was too long.Ignore the gearing, if you can get around it with a different prop.

[MBS1030]

Thanks for the help. I'm going to take the shaft with the pin to a machine shop and turn it down to accept the old style bearing and unit.