Mercruiser pre alpha(?) upper/lower interchangeability

[mbjeeper]

I recently bought a '79 Sea Ray with A Mercruiser 470, and within a short time the upper ring & pinion destroyed itself. The lower unit looks OK, so I am going to try to find a used or reconditioned upper, as I don't have the tools to set up the gears myself. Also, the sterndrive is not the one the boat came with, I was told by the prior owner.
My questions are about interchangeability. My upper gear tooth count was 24/24, which should make it a 1.65 ratio.My unit has the lifting eye cast on the top cover, which I am reading is a pre-alpha drive. It looks as though there were 2 pre alpha drives, an R and an MR. How can I determine which I have?
Also, as I look for a replacement upper unit, what will fit?
I have seen suggestions that anything 1983 or older will bolt onto my lower and gimbal housing, but of course I want to be sure. The only things that appear to be bad in my unit are the gears themselves, so i could still use my joints and shafts if I need them. It looks as though there was a difference in shaft length on some units. Are there any interchangeability issues that I need to know about?
Will later model upper units work?
I would like to get this boat back in the drink before it gets too cold this fall.Any help appreciated.
Thanks,
Greg
mbjeeper@aol.com

 

[Bt Doctur]

Re: Mercruiser pre alpha(?) upper/lower interchangeability

the 1.65 was used on inline 6`s ,i think the ratio for the 470 was 1.85.

 

[Haut Medoc]

Re: Mercruiser pre alpha(?) upper/lower interchangeability

I'm pretty sure Bt Docktur is right....
What part of Jersey, btw, BD?
Anyway, why don't you post up that serial # located on the engine by the heat exchanger or go to the Merc. site with the # & find out for sure.....
Also, if you shattered the gears as you say, then you probably have debris in the lower, (they are connected)..
The lower should be disassembled, cleaned & resealed at the very least....
I would hate to see you replace the upper & then have garbage from the old lower trash 'em both, JMHO.....
Ebay has aftermarket drives by SEI for A around $1300, not sure about shipping to UK, though......JK

 

[Bt Doctur]

Re: Mercruiser pre alpha(?) upper/lower interchangeability

near exit 9 NJTP

 

[Haut Medoc]

Re: Mercruiser pre alpha(?) upper/lower interchangeability

Raritan River, eh?