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I want to try to get the lower unit repainted over the winter months this year, now that I have access to the boat.

The original paint is pretty pitted. It almost looks like salt water damage - although the boat has been a fresh water runner for as far back as I was able to trace it.

Anyway, should the lower unit just be sanded and painted, or is there a filler that should be used to smooth out the finish even more. Or, is that a bad idea?

Aside from the surface pitting it's in pretty good shape for an engine it's age. (1984)

Any suggestions?

Thanks,

Perry

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I have repainted several lower units and skegs on my Mercury outboards, using Mercury's 3 stage painting system of primer, base color and clear coat. Results have been excellent, with factory like finish and gloss. I would assume BRP has a similar 3 stage paint system for your engine. Follow instructions on cans accurately, particularly with resect to TIMING of the three stages, and don't cut corners.

Begin by wet sanding the entire area to be painted with #400. If pitted areas do not sand down, fill them with automotive spot puttiy and sand smooth. You do not have to remove the original paint. Block sand the skeg edges to make them straight, square and true as they would have come from the factory.

After complete masking work, apply the three stages per instructions on the cans.

After curing for several weeks, wet sand the finished work lightly with #1500 and then #2000 grit.
This will get rid of any orange peel surface. Then orbital buff (wool pad) with Finesse-It II, followed by an automotive clear coat scratch remover like "Kit Scratch Out". Do tight corners by hand. The resulting finish will be high gloss and look "factory".

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Maybe it is the color, maybe it is the process used at the factory, Mercury Outboards had the best finishes. (at least the older ones) Anyone else with this observation? I have never owned a Mercury outboard.

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Yamaha yamaha yamaha

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It sounds like you have some galvanic corrosion going on, check your zincs and your gound connections. Replace zincs as needed. I hear there is a body filler that is used for under water purposes but I have no experience myself in that area. Be sure to use a zinc cromate to prime aluminum prior to painting. Good luck with your repairs.

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Zincs have been obsolete as outboard engine anodes for over 20 years, at least with Mercury/Mercruiser. Now, all of the manufacturers use aluminum as their anode material. Aluminum protects twice as well in salt as zinc, and is better protection for fresh water also, but magnesium, when available aftermarket, is now the high end choice for fresh water protection.

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Galvanic corrosion never occured to me. Ive never seen it like this on a fresh water boat before. Maybe its the 80s aluminum, but I never thought of needing an anode. The engine doesnt even have on on it. Given the condition of the wiring when I bought the boat and assuming it sat in the water I can see why it happened, but I ve just never seen it before in fresh water. Consider my eyes opened. I think an anode is now on the list.

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Took a look and "yup" no anode on the engine. It must have been in the water a lot. I've never seen a fresh water outboard surface corrode like this.

So, on a slightly different note: how difficult is it to pull the lower unit off this engine? Evinrude 90 V4. I'm considering it, but I don't want to open a can of worms either.

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Not too hard, You should get a repair manual for the motor usually available from your local marine shop or sometimes automotive shop or even the library, I had a 1980 100 horse Johnson and pulled the lower end off for water pump replacement. As I remember the most difficult part was disconnecting and reconnecting the shifting level. Can easily done in an hour or so. There are precautions about what position the shift lever is to be in for the removal and installation of the lower end. I hope this helps.

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Thanks for the advice.

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Probably a good time to replace the water pump if it has been more than a few years.

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Galvanic corrosion can happen anywhere.

If you are going to keep and dig into this engine, take time to try to find a real shop manual for it.
Generic manuals are good if that is all available.

Either will pay for themselves.

Good Luck

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Larry's (Finnegan) advice is sound, however, depending on the severity of the pitting, I'd consider going with a more aggressive sandpaper for the first pass - I use 80 grit to really get good bite and remove the flaky material. Then 100, 180, and 220. Then I use a self etching primer (Zinc Chromate is best, if you can source it locally). Then a filler primer if needed, which you can sand using 400 grit paper. Then put down the base/color coat as Larry suggests and WAIT!!! The Waiting is the hardest part, but it is also one of the most important. Let that base coat cure, cure cure. Use only oil-based OEM paint and let it cure for several weeks. I recently restored a 6 hp Johnson outboard and had to wait 5 weeks before it really cured well enough for final finish work and decals. The result was completely worthwhile.

I'm currently working on restoring the exterior paint on a pair of 1978 80 HP Mercs for my 1977 21 Outrage project. It is slow going, but the resulting finish will be worth it!