83 Pre-Alpha Anode installation - Magnesium

[BuzzM]

I am installing magnesium ( freshwater ) anode to my 83 prealpha outdrive. I noticed that aluminum acorn anodes that go on the to lower bolts had gaskets. The new magnesium ones did not come with gaskets.
I am putting a new block anode ( the one that goes over the trim fluid manifold tucked under the unit ). The old was was corroded to almost nothing, but there seemed to be a hardened material under it, either old rubber gasket or JB weld.
I think that it is better to have NO gasket so there is continuity,. Am I right?
Learning as I go, $$$.

 

[Don S]

Re: 83 Pre-Alpha Anode installation - Magnesium

I think that it is better to have NO gasket so there is continuity,. Am I right?
.

Wrong, thought. There is a thick gasket in there to stop possible leaks. Get one from your Merc dealer. The bolts makes the continuity. The part number is 27-99506 1
you also need to get the rubber gaskets for the bullets. They don't come with the anodes.

 

[BuzzM]

Re: 83 Pre-Alpha Anode installation - Magnesium

Thanks for the help. This noble metals, galvanic corrosion, etc. is a mystery to me, even though I've read a dozen articles. This raises another question, why don't I need a gasket for the new magnesium trim tab. As a matter of fact, I wire brushed the cavity to make sure I had good contact.
I appreciate the assist.

 

[Don S]

Re: 83 Pre-Alpha Anode installation - Magnesium

This raises another question, why don't I need a gasket for the new magnesium trim tab..

Who said you don't need it? Like I said before the bolts are for continuity. The gasket prevents leaks.
The anodes DO NOT come with the gasket, you need one.
Here's a link to section 7 of the Merc manual. Look at page 7A-3. (that's page 5 of Adobe Acrobat reader) and read it.
Look at the rest of that section also. It's all about corrosion prevention.

http://www.boatfix.com/merc/Servmanl/6/6A7R3.PDF

 

[BuzzM]

Re: 83 Pre-Alpha Anode installation - Magnesium

Pg 7 under anodic trim tab says that ( 3 ) scrap trim tab mating surface on gear housing down to bare metal. It says to be effective, the new trim tab must make good electrical contact with the gear housing. Thanks for the
link.

 

[Don S]

Re: 83 Pre-Alpha Anode installation - Magnesium

Pg 7 under anodic trim tab says that ( 3 ) scrap trim tab mating surface on gear housing down to bare metal.

Pay attention. We weren't talking about the trim tab anode, we were talking about the one over the trim hose manifold. The one with the gasket and rubber plug. Remember? ? ? ? ? ? ?
Go to page 7A-3 of that link and read it. Then move on to page 7A-4 discribing the anode we were discussing earlier.
Now, if you want to talk about the trim tab anode, that's fine, but don't use what is described for installing the trimtab anode as what is used for the one over the trim hoses.

 

[BuzzM]

Re: 83 Pre-Alpha Anode installation - Magnesium

Got it. Thanks.