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Is it an Alpha One?

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mike77cj

Regular Contributor
I'm a Volvo guy, but helping a friend do PM on his Mercruiser. He has a 1980 Alpha drive. Is this an Alpha One, or pre-Alpha One? When ordering the new raw water pump it asks. Does anyone have the part # by chance, as well?

Thanks!
 
mike77cj said:
  1. I'm a Volvo guy,
  2. but helping a friend do PM on his Mercruiser. He has a 1980 Alpha drive. Is this an Alpha One, or pre-Alpha One? When ordering the new raw water pump it asks. Does anyone have the part # by chance, as well?
Thanks!
Click to expand...

  1. Me too, Mike.... but keep that under your hat when posting in the Mercruiser section! :D
  2. I'm thinking that in 1980, this would be Pre-Alpha.... Even if Alpha, I believe that the sea water pumps were same until the next generation....... but the Merc guys can confirm.
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1980 you should be using the m r 1 alpha gen 1 kit, i would replace the whole thing with the newer housing and wear plates, they run 31 to 89 dollars for the whole kit and 12 to 24 for just an impeller kit
 
Based on the year alone, for the drives I looked at, the impeller kits all had the same part number: 46-96148A8.
 
The way to tell if it is a pre alpha 1 Gen I

I, R drives had the preload pin on the top of the vertical shaft. This used a different base design and a different impellor housing design.

When the MR came out ( and I am not 100% sure there was not a "transition period" ) But the MR came with the non preload pin vertical shaft this is when the base and housing for the water pump changed. It stayed the same until the alpha I gen II came out. It is also the same as in the large outboards.....
 
No matter what the drive year is, Go to your Mercruiser dealer and make sure you use a Mercruiser water pump. DO NOT USE A SIERRA PUMP! The hub will spin in the impeller of the sierra pump.
 
Dock, dont know if you did the mesco show, but they are aware of the past problem and claim to have rectified it.By the way had 2 merc impellers do the same thing.
 
I haven't tried a Sierra Pump for a merc since two summers ago. I know they pay labor and fees when there parts fail but I would rather use the OE Merc pumps. I have never had one fail at least not yet.
 
Thank you for all the input guys! I took the drive apart last night, it appears the vertical shaft has a preload pin, so I ordered the kit accordingly. The serial number was 5681986, I believe.

Could someone educate me on the order of the Merc drive, ie. "R" then Alpha etc.? Perhaps give a quick description of key features for each as well?

Thanks!
 
1 & I, R drives ( maybe others as well but before my time) PRELOAD PIN IN VERTICAL SHAFT. 19XX -1983

MR = pre alpha I gen I, basically the same as an alpha I gen I, vertical shaft has a oring groove like previous but no preload pin. 1984-1985-86ish

Alpha I gen I same as MR but NO oring groove on vertical shaft, no preload pin. 1985/6 ish to 1990

Alpha I gen II (new/current design..................1991 and newer.......

Now remeber we are talking 20-30 years and a lot can happen to these drives.......... so there can be some mix up on parts replacement on "like" drives.

These are just references............
 
Does anyone know if I could swap my 1989 alpha 1 gen 1 that was on a Chevy 305 to a a outdrive off of a 1983 mercruiser 470?
 
Last edited:
this post is over 7 years old and you should start your own post so it dosent get lost or buried
If the gears ratio is 1.84 it will work
 
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