Electrolysis plate on i/o drive replacement question

[DCS30]

Hi all. We have a 1978 Starcraft i/o with a 1977 OMC drive. Currently, the boat is going through brutal electrolysis, and I've been working on trying to narrow down the culprits, and am now turning my attention back to the plate on the drive. Plate that's on there is original, and honestly doesn't LOOK bad at all, but I'm wondering if it's out of "juice", so to speak, and maybe isn't doing the job properly. I can't seem to find another magnesium one, but my local marina is saying aluminum would be a decent replacement for freshwater. Can someone explain that one to me? An aluminum plate on a drive is going to distract from the aluminum hull? And has anyone replaced a magnesium plate on their drive with an aluminum?

Thanks.

 

[dingbat]

I can't seem to find another magnesium one, but my local marina is saying aluminum would be a decent replacement for freshwater. Can someone explain that one to me? An aluminum plate on a drive is going to distract from the aluminum hull?

Well, pure aluminum is extremely soft and pliable. Think soda/pop cans.

To make aluminum stronger, they alloy it with a numbers of different elements to for specific uses.
Chemistry Data :
This is the composition of 5050 aluminum alloy

Aluminum		Balance​
Chromium		0.1 max​
Copper		0.2 max​
Iron		0.7 max​
Magnesium		1.1 - 1.8​
Manganese		0.1 max​
Remainder Each		0.05 max​
Remainder Total		0.15 max​
Silicon		0.4 max​
Zinc		0.25 max​

As you can see below the addition of iridium raises the activity to that above aluminum.

I suspect that your an anode (plate) and hardware connections are pretty well oxidized after 45+ years. You could remove and try to make "shiny" again, but you would be better off to replace and move on.

 

[1960 Starflite]

On our lake I have to run magnesium anodes on my Merc IO. Aluminum does nothing and elements eat up lower unit. Be careful ordering online. I ordered magnesium from an East coast vender, they sent aluminum.

 

[Bondo]

Hi all. We have a 1978 Starcraft i/o with a 1977 OMC drive. Currently, the boat is going through brutal electrolysis, and I've been working on trying to narrow down the culprits, and am now turning my attention back to the plate on the drive. Plate that's on there is original, and honestly doesn't LOOK bad at all, but I'm wondering if it's out of "juice", so to speak, and maybe isn't doing the job properly. I can't seem to find another magnesium one, but my local marina is saying aluminum would be a decent replacement for freshwater. Can someone explain that one to me? An aluminum plate on a drive is going to distract from the aluminum hull? And has anyone replaced a magnesium plate on their drive with an aluminum?

Thanks.

Ayuh,...... Hit it with a wire brush on an angle grinder,....

Shiny metal is active metal,....

 

[DCS30]

Ayuh,...... Hit it with a wire brush on an angle grinder,....

Shiny metal is active metal,....

tried it already. no change.

 

[DCS30]

Well, pure aluminum is extremely soft and pliable. Think soda/pop cans.

To make aluminum stronger, they alloy it with a numbers of different elements to for specific uses.
Chemistry Data :
This is the composition of 5050 aluminum alloy

Aluminum		Balance​
Chromium		0.1 max​
Copper		0.2 max​
Iron		0.7 max​
Magnesium		1.1 - 1.8​
Manganese		0.1 max​
Remainder Each		0.05 max​
Remainder Total		0.15 max​
Silicon		0.4 max​
Zinc		0.25 max​

As you can see below the addition of iridium raises the activity to that above aluminum.

I suspect that your an anode (plate) and hardware connections are pretty well oxidized after 45+ years. You could remove and try to make "shiny" again, but you would be better off to replace and move on.

i agree...the problem is finding a magnesium plate. aluminum is for "mixed", which scares me, hence the question. i'm a just a little leery haha

just to follow-up, you're saying that the aluminum plate that i would order would not be pure aluminum, correct?

 

[DCS30]

On our lake I have to run magnesium anodes on my Merc IO. Aluminum does nothing and elements eat up lower unit. Be careful ordering online. I ordered magnesium from an East coast vender, they sent aluminum.

did you end up finding a magnesium plate?

 

[1960 Starflite]

did you end up finding a magnesium plate?

I did. I looked up the specific gravity of magnesium, zinc and aluminum. Transfered postal weight scale to garage workbench. Figured the mass off what was shipped to discover they sent aluminum not magnesium. Once in hand, you can feel (weight) the difference. It was a rectangle plate for hull mounting, I modified it to fit.

 

[DCS30]

i decided to REALLY give it a good grind down, and holy hell, was there a lot of build up on it. it deceived me because it just turns dark grey, whereas the plates on the outboard get all lumpy. this thing is now shining to the point it will blind you in the sunlight. since i can't seem to find a magnesium plate in my area, i may roll the dice on the old, cleaned up one.