850 Lower Unit Fit 1000 6 Cyl.?

[77sprite]

I tore apart my '77 850 to find a broken crank, so now I need an engine. Will a '69 1000 6 cyl. Thunderbolt fit my '77 850 4 cyl. Thunderbolt #4594650 lower unit? I won't be using the lower unit from the 1000 b/c it's cracked. Thanks!

 

[emckelvy]

Re: 850 Lower Unit Fit 1000 6 Cyl.?

The 4-cyl lower unit will bolt right up, and the I-6 will like the 85hp L/U's 2.3:1 gear ratio. Depending upon your existing prop you may have to change the pitch to account for the difference in gearing and the extra torque/hp of the Six.

The old motor likely has an O-ring groove at the end of the driveshaft, this seals the crank splines so they don't rust away/freeze the driveshaft to the crankshaft. If the newer lower unit doesn't have this O-ring groove, you'll need to grind one into the shaft in the same place. I've used a grinding or cutoff wheel chucked into an electric drill motor in the past, this'll do a serviceable job.

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

 

[77sprite]

Re: 850 Lower Unit Fit 1000 6 Cyl.?

That's great news. Any links to threads covering this procedure to modify the shaft for the o-ring groove?

 

[emckelvy]

Re: 850 Lower Unit Fit 1000 6 Cyl.?

Pretty much as described. There's a groove in one driveshaft; make the other look the same!

The groove doesn't have to be perfect, just needs to be in the same general location as the other one. Probably the best way to measure is from the 'flange' of the gearcase, up to the O-ring groove. Then transfer those measurements over to the other driveshaft.

If I recall on the last one I did, a cutoff wheel (not a grinding wheel) was skinny enough to make a groove of the correct width. Then, you just need to grind it evenly all around the shaft and make sure it's deep enough to hold the O-ring. Use the fitment of the old groove as a guide.

Anyhow, that's about all there is to it. HTH..........ed

 

[Faztbullet]

Re: 850 Lower Unit Fit 1000 6 Cyl.?

My inline on my houseboat did not like the 2.3 ratio last year so went back to the 2.1..1969 950SS with NEW factory powerhead