TOPIC: 2 blade prop on a 950SS

I just picked up an 80 hp 1969 merc to use the lower unit off of. I am going to use it on my 66 950 SS. The 80 Hp came with a 19 pitch 2 blade prop. should I run it?

depends on boat size and the gear ratio. is the ratio the same as the 950?

The 950-6 had 2:1 gears from the factory.

A '69 800-4 had 2.3:1 gear ratio.

The 950 will spin that 2.3:1 gearbox with verve! It'll like it a lot!

The effective pitch of that 19" prop and 2.3:1 gears is around the same as if the 950 with 2:1 gears were swinging a 17" pitch prop.

It'll probably push Ol' Blue OK, if not drop down to a 17" pitch 3-blade and it'll likely be perfect. Just depends on how heavy Ol' Blue is and what prop is being used currently.

Nice thing is, the 2.3:1 gearbox lets the motor rev up easier and you get a wider selection of props to choose from, since you can use a higher-pitched prop than you could with the stock 2:1 gears.

One caveat, if the donor lower unit's driveshaft doesn't have an O-ring groove up by the splines, you'll have to grind-in a groove to retain the O-ring which seals the crank/driveshaft splines. Later models used a stainless carrier pressed into the end of the crankshaft, inside this carrier resides the O-ring. Such that the driveshaft is smooth and seals on the O-ring up in the crank.

The 950 doesn't have that seal assy on the end of the crank, it relies on the driveshaft O-ring to seal on the i.d. of the crank.

If you put the a later-model lower unit without an O-ring groove into an older motor which requires one, water will get into the splines and rot/rust out.

My good buddy Dr. Frankenmerc (Thom) recently did a lot of work to a guy's old 650 with a newer lower unit, and I was standing on the dock watching, when they tried to take off and the crank splines went.

An ugly sound to say the least! No seal on the crank and no O-ring on the shaft lead to Zero Splines in the crankshaft!!! And another motor for the old G3!

HTH & let us know how it runs........ed

Ed, I am always amazed by the level of knowledge some of you guys have. Thank you for the additional info. I bought the 80HP for the soul purpose of changing up that gear ratio from 2:1 to 2.3:1, in hopes that it will make a difference in how Old Blue gets out of the hole, as well as top speed. right now I am running a 19 pitch 3 blade prop, and at the altitude that I am running at on a regular basis (7800) she is slugish out of the hole, and if I have more than a couple of people on board, I have to have everyone stand as far forward as I can get them to come up on plane.....

Smitty,
Be sure and check the lower shift shaft length and style of reverse lock cams on it. If they are the same length and visibly the same reverse lock parts - no biggie, but if not, it calls for more than a little finessing to make the 950ss reverse lock cams fit down into the 800's housing.
If the shift shaft in the 800 is too long, you can cut it off to match the 950ss length, but if the 800 is the shorter of the two, ask for instructions on how to R&R the shift shaft without a total tear down.
doc Frankenmerc

Well........This is all for not at this point!!!!! the 800 that I bought supposedly had a great lower unit that had a somewhat fresh overhaul done on it....well lets just say that I learned a lesson on buying used from someone that I do not know!!! I started tearing down the 800 tonight and found that the lower unit is stuck in gear and will not come out, and I can tell by looking at it that it has never been overhauled, in fact it looks like the water pump is still the original!! At least I go 2 prop out of the deal, and hopefully there are enough interchangeable usable parts to make it worth the $100 that I paid for this motor...

might be just gone over cam and can be forced backby turning the shaft can be a bear to do if lucky.

OR,...
If you can rotate the driveshaft clockwise and the propshaft rotates counter-clockwise,...See if you can rotate the shift shaft counter-clockwise about 1/2 a revolution and magically find Forward gear. Then a very short & careful counter-clockwise rotation to the next 'bump' you feel and find that the propshaft rotates both ways silently (Neutral)
Then,...When you attempt to continue turning the shift shaft counter-clockwise - - manually rotate the prop shaft with one hand - rotating it clockwise as you attempt the counter-clockwise rotation of the shift shaft a smidge to Reverse.
Please let us know if this resolves it - or if you are still on the hunt for a long shaft 2.31:1, which I just happen to have,...Or I am more than willing to investigate and potentially repair the 2.31 you already have.
Doc F

Dr Fankenmerk,
Where are you located? I am in Utah, and I am curious as to what you might want for a good lower unit with the 2.3:1 ratio. I will play with the one that I have a little more tonight when I get home from work, but it would be good to have a back up plan.....

Smitty,
I'm located in Shelton, WA 98584.
I have both long shaft & short shaft 2.31:1 units & will do the required modifications to make the reverse lock work properly under a 950ss.
Please feel free to contact me via e-mail at:
frankenmerc at comcast dot net or call me at:
3sixty, two eighty, 8two,1seven during appropriate hours PDT.
I would be willing to investigate and correct the problems in your 2.31 or simply set you up with a nice one from my 'stash'.
Please feel free to question my honesty & commitment to old Mercs with anyone on the forum - or elsewhere.
Thom

I can fully vouch for the Good Doctor!

BTW I'm thinkin' the reverse lock on the '66 950 is already the "modern" design with plastic shift lock cam slid over the shift shaft & fitting down in the recess.

Wasn't '64 the last year of the brass interlocked cams??

Pretty sure they made the L/U change-over the same year ('65) they went to rubber-isolated inner cowling brackets & telltale thru a hose rather than thru a hole in the lower cowl/exhaust adapter.

Just a thought........ed

And,...Based on the parts break-down,...Once again I must bow to my Mercury Yoda, ed_mc, who has taught me so very much about these awesome creatures.
Thanks Ed,...That should resolve that issue for Smitty and make the exchange MUCH easier.
Thom

Dr_Frankenmerc wrote:

Smitty,
I'm located in Shelton, WA 98584.
I have both long shaft & short shaft 2.31:1 units & will do the required modifications to make the reverse lock work properly under a 950ss.
Please feel free to contact me via e-mail at:
frankenmerc at comcast dot net or call me at:
3sixty, two eighty, 8two,1seven during appropriate hours PDT.
I would be willing to investigate and correct the problems in your 2.31 or simply set you up with a nice one from my 'stash'.
Please feel free to question my honesty & commitment to old Mercs with anyone on the forum - or elsewhere.
Thom

I can 100% vouch for Dr Frankenmerc! He is a top notch character, a Merc Guru, and an all around A+ guy! He has done work for me, and helped me tremendously in my Mercury addiction.