How do i fix Alpha One Gen 1 lower unit leak?

[RDJuhl]

Hi,
I purchased a 1989 Larson used boat (3.0 engine) which is powered by a Mercruiser Alpha One Lower Unit.
Lower Unit Serial Number 0C787706 (I believe this is a Alpha One Generation 1 unit)

We have had a small lower unit leak from the weep hole since we purchased it. I took the lower unit to a repair shop who pressure tested the lower unit. He identified the leak as below the water pump. It took him several attempts to seal it...trying a combination of old and new water pumps and gaskets. He finally told me it was fixed, and held pressure. I paid him $100 for this repair.

About a month later, I was prepping the boat for a launch, and ran it on muffs in the driveway. Lower unit oil was "oozing" out of the weep hole. I never did get the boat in the water this year...as I was afraid of doing some damage.

Time is now permitting me to winterize the boat...and hopefully, take care of this issue once and for all. I have received a Sierra Seal Kit 18-2652. I did pressure test myself today. It appears the base of the water pump is leaking again.

Attached are a few pics showing the lower unit, water pump, etc.

Question...why would the water pump not seal? What can I do differently from what the repair shop did?
Thanks for any advice!

 

[Rick Stephens]

How beat up is the shaft? Did the water pump base get replaced along with the seal? You may have to clean up the shaft, and replacing the pump base with the seal is a no brainer. It also has an o-ring around the outer part of the seal housing that can get pinched and damaged.

 

[RDJuhl]

The shaft looks to be in good shape. I think the mechanic who did the work had tried a new pump...and that did not hold either. Guess I will locate a new pump and base in the AM and hope that fixes it.

 

[thumpar]

Are you pressure testing as a complete unit or halves?

 

[RDJuhl]

I pressure tested the whole unit before splitting tha halves. I could not get a reading. After splitting, I haave a large air leak under the water pump.

 

[thumpar]

Since you tested it as a unit I would test the halves and spray soapy water on it. You can plug the oil passage.

 

[Bt Doctur]

you will have to remove the pump base to inspect the housing for corrosion. might even have the wrong gasket in there or the wrong pump base. post a pic of the base you removed. That is a R/ MR type not a MC1 type

 

[RDJuhl]

you will have to remove the pump base to inspect the housing for corrosion. might even have the wrong gasket in there or the wrong pump base. post a pic of the base you removed. That is a R/ MR type not a MC1 type

You are correct....my old pump base is the wrong one. I took the old pump base to the local parts house...and the part did not match up to the serial number of the lower unit. He finally found the right part...and after assembly, no leaks what so-ever. I tested the lower unit separately, then tested again after putting the two haves together.

You indicate this is a R/MR type rather than a MC 1 type. The serial number on the drive starts with 0C....can you elaborate on the difference?


The attached photo shows the old base compared to the correct part.
The "shoulder" of the old base was very narrow...preventing a seal around the edge. The mechanic who worked on this a few months ago seemed to like using a lot of gasket sealer instead of using the correct part.

Thanks for your help!

I think I now have the boat ready for spring!!!

 

[Rick Stephens]

You are correct....my old pump base is the wrong one. I

Bt Doc nails another one. Righteous resolution.

 

[Bt Doctur]

Every now and then I get a few right. Ever see a 6 cylinder trigger wheel in place of a V8 one?
Had one yesterday that was very strange. dual tanks with a single feed and barely made it to the marina
. Running out of gas symptom .
We removed the anti-syphon and what came running out looked like cement slurry. Thinking the ethanol is dissolving the alum tanks . Has the same look as the residue left in a carb that had water in it.

 

[Bt Doctur]

The MC1 and the R use the same pump base because the driveshaft uses a preload pin,. the MR uses the base in the new pic because the driveshaft does not have a preload pin.