# WTB, I/O Alpha one lower gearcase/unit; but do they interchange?



## BIGRIGZ

My dad needs to find a Mercruiser Alpha One outdrive lower gearcase (ie lower unit). It'sfor a project boat he bought.

Does anyone know if the I/O lower units are interchangeable with other _outboard _lower units etc.

He really only needs the lower unit but, I'm thinking it may be wise for him to find a whole outdrive in case he ends up needing it.

He hasa 1984 19 1/2' Searay with a 260HP 5.7L Chevy 350cid it is a Alpha One outdrive ratio = 1.98 "R" (it looks to be CCW rotation).

Any tips on a salvage yard or contacts is much appreciated, I'm looking on Ebay and Craigslist regularly.

Thanks, Ken


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## sosmarine

The "R" after the ratio just stands for Ratio, not CCW. If it is single motor then the O/D is standard rotation. I have an Alpha Gen II that came of a 3.0 Litre so the ratio is wrong but the gears can be changed.


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## BIGRIGZ

I clarified with my dad: the prop turns clockwise. He got the CCW marking off of the valve cover for the engine, I'm not sure what it means?

http://www.sterndrive.info/sterndriveparts/identify_my_outdrive.html










according to this website the model we have is used from 1984-1992.



Do you thinkyou know of a lower unit that would work for us?

thanks, Ken


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## BIGRIGZ

SOS, we were thinking that we could put his gears into a different lower unit housing when we found one if it wasn't the right gear ratio etc. BUT, that's where we really don't know what lower unit housings might be interchangeable...


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## Tuna Man

> *BIGRIGZ (1/7/2008)*SOS, we were thinking that we could put his gears into a different lower unit housing when we found one if it wasn't the right gear ratio etc. BUT, that's where we really don't know what lower unit housings might be interchangeable...


All Alpha I's Lower Unit (not the Pre Alpha with the lift ring/or the pre-load nipple on top of the shaft) are interchangeable. The difference in the gear ratio will be in the Upper Unit. Alpha I Gen II not interchangeable. Meaning a Alpha I upper unit and a Alpha I Gen II lower unit,put together.

All single engine I/O's are CW. You will find out that in a 2 engine set-up one will be CW and the other MIGHT be either a CW or a CCW

What puzzles me is that you say it is a 1.98:1 ratio. When the 350cui/260hp came factory with a 1.50:1 with a optional 1.32.1. The lower gear ratios of 1.65:1..1.84:1..and the 1.98:1 , I thought were for the 4 and 6 cylinder, and smaller V-8engines.:banghead I do stand to be corrected.

CCW off the valve cover could be that the valve covers are aftermarket.

Your Alpha-I shift shaft...1984-1992










The Pre Alpha shift shaft...not yours. 1972-1983










Note the Pre-Load pin on the shaft (top right of photo)


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## Tuna Man

After a little research I found this chart.... The 1.98:1 came with the 2.5 and 3.0 both being 4 cylinder,from 1986 to 1992










So that leads me to say that I think you have the wrong Outdrive ratio for what engine you say you have. Someone might of swaped the outdrive not knowing/careing the difference.


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## sosmarine

I missed the year of your unit. My Gen II will not work for you. I can get you a remanufactured lower unit.

As for the gear ratio you have now, it could have been rebuilt with a different ratio than what is stamped from the factory.


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## Tuna Man

> *sosmarine (1/8/2008)*I missed the year of your unit. My Gen II will not work for you. I can get you a remanufactured lower unit.
> 
> As for the gear ratio you have now, it could have been rebuilt with a different ratio than what is stamped from the factory.


Thanks for backing me up on this one. I thought I had it right and knew that if I needed to be corrected that it would come out and I'd eat some crow. As for the gear ratio, do you think that a 1.98:1 would even work on that boat with the 350ci/260hp?








okeokeoke Sometimes we get tunnel vision.


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## BIGRIGZ

I had my dad check the ratio of his outdrive by turning the input shaft and counting the ratio to prop turns. It is in fact a 1.50:1 not 1.98:1 Someone must have put the (1.50:1) gears in a different(1.98:1) housing. 

I have another outdrive that I came up with but, I'm not sure what it is...

I'm pretty sure it is a Pre-Alpha because of the preload pin on the drive shaft that Tunaman posted a picture about.

Although, the top cap on the upper gearcase looks more like an Alpha one. 

I have read some information on other online forums that there was an Alpha one unit which used the preload pin.

Can anyone verify this info using these pics?


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## Tuna Man

Did you save the link to those pages you looked at. I would like to read them.

Top picture is your lower unit. Bottom is mine. I know this is a alignment pin.

Your first picture to me looks like a AlphaI, as far as the cap goes. I don't know if the caps are interchangeable or not.

Your second picture shows a (what I can make out) a pre-load shaft.

Your third, forth, and fifth pictures show your lower unit and what appears a alignment pin on the opposite side of mine.

I'm still trying to figure out what you are trying to do with the outdrive.:banghead:banghead


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## BIGRIGZ

Here is a pic of the broken lower unit. It's off of his '84, supposed to be an Alpha One. I'm kinda confused now cuz of the locator pin on the port side of his lower unit and the fact that he has the NON-preload shift shaft...

Anywhoo, It looks like his housing is the same as the one I have off of an '83so, I expect he'll be able to put his guts into this lower unit case that I have?


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## SonShine Fishing

I have a 1984 SeaRay with 260 Horse Mercruiser. I have been through just about everything on the boat. He has an R drive which is a early version of the alpha 1 gen 1. Next was MR then plain Alpha one. The R outdrive has a preload pin in the top of the driveshaft going into the lower unit. It is a spring loaded pin sticking up above the splines on the end of the shaft. This spring loaded pin sets the preload on the upper bearing in the lower unit. All later outdrives have the preload set with shims. I am pretty sure any alpha one gen one lower unit will work and the gear ratio is determined by the gears in the upper unit.


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