R drive compatibility?

[s.hadley81]

Hey guys I have what I think is a mercruiser r drive that came on my boat when I bought it, the motor in the boat is the original 89 2.5l 120hp. I know it's not original to the boat but it worked fine after I resealed the upper. I got a season and a half and a lot of hours out of it before it developed a water pocket leak and when I tried to replace the water pocket gasket all 4 bolts snapped off. I had a perfectly fine alpha one(serial # ob5643790) that I picked up of Craigslist so I threw that on. So basically I have a trashed upper housing with good gears. So Do the mr and alpha use the same gearset? I know the lower will work but is it worth saving the gears and bearings out of the mr for spare parts for the alpha drive? i wish I could find a serial number on the old drive but there is nothing on it but I know it's old because under the Cap it has a kiekhafer stamp on it. It might even be an Mc-1 I'm not sure how to tell the difference between a mr and a mc-1.

 

[Starcraft5834]

trying to understand what your saying... what part of your drive is ok? upper or lower?... what's the ratio? 1.98?, once you sort that out, give SEI a call

http://www.sterndrive.cc/

 

[Bondo]

So Do the mr and alpha use the same gearset? I know the lower will work but is it worth saving the gears and bearings out of the mr for spare parts for the alpha drive?

Ayuh,..... There's a quite abit of overlap in the changes to the Alphas/ MC-1s,....

The only way to know for Sure is to dig into the parts books, 'n cross reference the part numbers,....

With the price of the aftermarket drives, gettin' a drive rebuilt ain't hardly worth the money anymore,...

 

[s.hadley81]

Thanks bondo, the alpha drive I'm running now is perfectly fine but just figured I'd pull apart the trashed Mc-1 upper and throw the gears on the shelf in case I could use them. Like you said it's probably not worth it with the cost of a aftermarket one. so I'll just keep the mc-1 lower for a spare. Thanks again

 

[Fun Times]

Alpha one(serial # ob5643790)

You have one to many numbers in this serial number but using 0B564379 says it's an MERCRUISER MC1 1.98:1.

So basically I have a trashed upper housing with good gears.

If you're able to get the rest of the bolts out, wouldn't the upper drive shaft housing still be good? With a good search sometimes you can run across a good company that might be able to extract the broken bolts. Here's an example if interested, http://cammann.com/

So Do the mr and alpha use the same gear set? I know the lower will work but is it worth saving the gears and bearings out of the mr for spare parts for the alpha drive? i wish I could find a serial number on the old drive but there is nothing on it but I know it's old because under the Cap it has a kiekhafer stamp on it. It might even be an Mc-1 I'm not sure how to tell the difference between a mr and a mc-1.

If you happen to know what engine size/model the other drive came off of might help give an indication of what gear ratio it may have been....But the best ways to know would be by counting the gears then search either online or in the manual for a gear tooth count to gear ratio chart or the other way is turn the input shaft and count the prop shaft rotation.
https://www.seilermarine.com/info/mercruiser-drive-ratio-chart.php

If it's still working, Don S put together a nice history document on the Alpha drives that might help too, How to ID an Alpha Style Outdrive, and History.
Mercruiser Alpha ID and History.pdf - 4shared.com - document sharing - download - Don S