Zinc paint ok on Yahama lower unit part??

R

Roy & Dixie

New member
My recently purchased 1999 22 CD cruiser has a 1999 80hp Yahama engine. The motor for the trim/tilt hydraulic pump had began to rust and a previous owner sprayed the steel motor with a grey paint, which seems to have made a bad situation worse. The added paint trapped water under the paint, causing the motor housing to develop a thick layer of rust scale, to the point of flaking off in chunks. I did not notice this until I was cleaning the boat after purchase. I have scraped and sanded the rusted areas down to solid metal and coated the steel motor with Ospho (phosphoric acid). I watched the area where that motor is bolted to the Yahama and see that the Ospho had no adverse effect on any other metal surfaces. The rusted areas of the hydraulic motor are now coated with iron oxide, as promised by Ospho. I need to paint with a good paint to protect the motor against any further damage. Would other areas of the Yahama lower unit be affected by the use of zinc paint as a primer? I have heard aluminum would be affected. A new pump motor would cost $770 dollars, I was told, so I need to save and protect what I have. I will be boating locally on Fla inland rivers which are fresh water, but I do plan to do extensive ICW coastal cruising between the Fla Keys and the Chesapeake in the near frture.
 
I always understood zinc chromate to be the primer one was supposed to use on aluminum. I believe it helps tie the paint to the metal. It kind of makes sense that it would be okay, since zinc is less noble than aluminum.

I used some to prime the inside edges of the holes when I drilled for the Permatrim on my Yamaha. I had a hard time finding it in the paint department, until I found it in the "marine" area and made by Moeller. It's typically yellow.

I wonder if people who said it was a no-no were thinking of copper (like in bottom paint)? That's not a good paint to use on aluminum (more noble).

Be interested to hear what others say.

Sunbeam
 
Before the phosphoric acid treatment, you have to get all of the loose and built up rust scale off. Generally phosphoric acid works will with light rusted areas. If the scale is thick, and water gets under it again, it will just corrode.

If you want the best paint for this application-it is going to be "Rust Bar" by International. There are a number of different formulae, but it is available in black for steel. This is what is used in commercial applications where there may be immersion.
 
I used a 2 part epoxy primer (Sikkens) on my sterndrive followed with a gloss black rust paint. It looked good but I'm not sure how well it stood up as it was on my old Campion hard top which I traded in.

Regards, Rob
 
I've saved T/T units that are severely rusted by coating thickly with lanolin grease-it's extended the life of some that would have never made it otherwise-just slather it on thickly. It sticks well even in hot salt water.
Roger
 
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