Bravo One lower unit corrosion / paint blistering

[davidh82]

Hey CSR!! I have a bit of paint blistering on the lower unit of my bravo one drive and I was hoping to hear from you guys to see if anybody has any insight to offer. I first noticed the paint blistering when I purchased the boat a couple of months ago but just yesterday noticed that there are two areas slightly bigger than a quarter sized where the paint has come off.

My plan of action is to use a 120 grit dremel flapwheel to remove the corrosion, then use something like marine-tex to fill any pitting that is left behind after the grinding. After that I will apply two coats of zinc-chromate primer to any exposed metal. I also plan on painting over the entire lower unit since there is part of the paint that was rubbed off just behind the propeller (be careful that you don't let your dock lines fall in the water!). What I will do is take a 1000 grit paper and wet sand the rest of the lower unit, then paint it with a few coats of outdrive paint (from a spray can) and perhaps clear coat it.

Does anybody have any thoughts on the corrosion or my plan of action? I'm still trying to decide whether or not I should remove the lower unit. Since some of the corrosion is in the edge between the upper and lower units I'm a bit worried that there might be damaged areas that are not exposed. Thoughts? What seals would I need if I decided to pull just the lower? Is it difficult to remove and install the lower unit?

Thanks for reading, and I appreciate any feedback or advice offered. Below I am going to try to upload a few pictures showing the outdrive.

 

[davidh82]

I see that I have a few views on this post, so I figured that I would update in case someone has anything to offer or is facing a similar issue.

I decided to pull the lower unit to repair the corrosion instead of leaving it attached. I'm pretty glad that I made this decision since there was more paint blistering on the inside top of the gear housing. Fortunately, when I started sanding down the blisters with the 120 grit flapwheel and 150 grit sandpaper I found that the aluminum underneath was actually in very good condition. I expected to have to grind away and fill in with marinetex, instead I just had to sand down all of the blisters and paint that was lifting.

Once I finished sanding I put on a couple coats of zinc chromate. Tomorrow I will probably use a 400 or 1000 grit sandpaper on the zinc chromate to level it with the existing black paint, then I will give it a few good coats of outdrive paint.

Here is a picture of the gear housing with the paint blisters sanded away. Again, any suggestions or advice are greatly appreciated!

 

[Dave S]

Nice work.

i have had to deal with corrosion on my Bravo III drive for years since my boat since in the water year round. Your corrosion was very minor compared to what I have had to deal with. I think your prep work will give you a good solid basis for the finish coat. I have used Zinc Chromate myself and the only thing negative I have to say about it relative to my own experience, is the finish coat of black paint turns dull after the drive sits in the water for a period of time.

Keep in mind the factory paint is much better than what you can do on your own so don't remove any more of it than is necessary.

 

[davidh82]

Hey Dave, thanks for your reply and feedback. I've seen pictures of how bad the corrosion can get, especially on the bravo III and I don't envy you. Have you looked into testing your mercathode system?

This little bit of corrosion was probably something I could have let linger for a bit, but I figured it was better to fix it ASAP and avoid any damage to the aluminum. Also, I wanted the experience of removing the lower unit so that I wouldn't be intimidated by this in the future.

I have read elsewhere what you are saying about the factory paint. On 99% of the housing where the paint was not blistered I only went over the paint lightly with 1000 grit to scuff the surface and give the fresh paint something to stick to.

Here are a few pictures of the progress, I've already purchased the new seals and plan on installing the drive on Saturday after it has had some time to dry.