Alpha One Bearing Carrier Question

[76SeaRay]

I disassembled my used Alpha One Gen One lower unit (I don't have a serial number for it) and after looking at the bearing carrier it looks like I should replace it. My question is about the key way I found. The lower unit housing has a key way on the top and the bottom where the carrier slides in. The old carrier has a key on one side so I assume this key and key way is intended to keep the carrier from spinning with the rotation of the prop shaft. As near as I can tell, the part number for the bearing carrier is 818763A10. The new replacement bearing carriers I am finding under this part number do not have the key way. My old carrier used a large ring nut and large ring with locking tabs to keep the nut from coming off. So, I don't see a way to keep the replacement carrier from spinning without using the key and key way. Can anybody shed some light on this?

Thanks....

 

[jakedaawg]

Bearing carriers are a dime a dozen at most shops...if you walked into my shop I'd send you to the pile and you could pick a decent one out. I'm sure most shops would be similiar.

 

[76SeaRay]

I don't have any shops in my area like you describe. Anyway, is a bearing housing that does not have a key way ok to use and how is it different from the housing that uses a key way.. My Mercruiser manual #6 calls for the key..

 

[76SeaRay]

I am having a hard time finding the right carrier. I have looked at a lot of pictures for the 818763A10 which is what most parts diagrams says is correct for 1984 to 1990. Some have a key way slot and some don't. Apparently there was a 1983 design, a 1984 design, and a 1985 to 1990 or 1994 design. My drive has the carrier pictured above, has an "A" stamped in the end of the prop shaft, and does not have a pin at the top of the drive shaft.

So, is this correct?

73020A14 Early Alpha One Gen One
818763A10 with key way (Conversion Kit to Extra Zinc round prop shaft Early Alpha One)
818763A10 no Key Way with Extra Zinc Late Alpha One Gen One and Gen Two

They all seem to have the same casting number 73020 which is what my old one has...

 

[76SeaRay]

Well, I finally found a serial number on the upper unit for the drive after removing the labels and paint. Based upon the PPT site that you can look up parts by drive serial number, I found that my drive is a:

MERCRUISER

1985

MC1

01508015

R/MR ALPHA ONE STERNDRIVE

The bearing carrier called out in the parts diagram is the 73020A14. Looking at a picture of that one, it has the key way slot. So, looks like mystery solved and at least now I have the drive serial number. I ordered a 73020A14 and, due to a corrosion hole through the side of the housing, I ordered a new lower unit housing 1623-8951A37.

 

[76SeaRay]

Back to this question. I did receive the bearing carrier and new housing but had to return the housing since it was for an R drive and not an MR drive. I bought another new Quicksilver housing (1623-8951A27) that is correct of an MR drive. The new housing came with a new bearing carrier, a new upper pinion bearing, package of o-rings and a small note sheet.

The note says:

"IMPORTANT: Use new bearing carrier and new tab washer when using this gear housing as a replacement for a Right Hand (RH) Rotation MR or Alpha One. New gear housing and bearing carrier do not have a key and keyway.
When using this gear housing as a replacement for a Left Hand (LH) Rotation Alpha One, DO NOT USE NEW BEARING CARRIER. The new tab washer may be used."

I pulled this sterndrive from a single engine 19ft runabout so I would believe it is a Standard Rotation and the parts all seem to check out as standard rotation. Now, is Standard Rotation RH or LH in the context of the Quicksilver note that came with the housing??

My original drive (s/n 6908762) had a carrier with a key. I have a brand new carrier with a key and now this additional brand new carrier without the key. Contrary to the note above, the new housing does have a key slot on the bottom. So I just need to figure out which one to install. Implied but not stated in the note is that the LH rotation requires the keyed carrier. Does this now explain why some have a key and others don't. That is, on a LH rotation, the key is required to make sure the carrier can't unscrew the carrier retainer ring with rotation of the propshaft (assuming LH rotation is counterclockwise looking from the stern towards the front of the boat)??

 

[76SeaRay]

Still not sure which carrier to use but in trying to get my head around the gears and rotation, I created the following chart. Please look this over and let me know if I have it correct or not (I may be totally out to lunch)? I can easily modify it to make any corrections/additions. Thought it might help others... If it is verified correct for forward gear, I can add rotation to the chart for reverse gear. Thanks....

 

[76SeaRay]

After hours of searching I was able to find that the bearing carrier with the key way is used on a standard rotation and the one without the key way is used on a counter rotation set up.

 

[Rick Stephens]

At least you're not going where no man has gone before. However, it is a place I've never been. What a mess of dated information to trudge through.

 

[76SeaRay]

Definitely learning a lot by doing the whole drive myself as a complete restoration. It’s all the little things and watching them closely. Like, I just pressed the new bearing, thrust washer and reverse gear into the bearing carrier. The oring went on fine but looking at it on there it looks like the ring is too small in diameter to seal properly to the case. Another small detail to sort out.