Repairing lower unit surface

Hey. I am hoping for some advice with this. On my '85 Force, there is a fair amount of corrosion on my LU. For the first 20 years of it'slife it say in water for 6 months out of the year. And it's definitely shows the signs of that now.



I need to keep to a pretty tight budget, and not sure what is required to get her looking new(ish). The pits aren't too deep, but if left unchecked I fear they will eventually go completely through. So, what prodoct (bondo-esque?) can I use and then what types of paints? Does it have to marine paint or can I use regular paint? Thanks!

Re: Repairing lower unit surface

Your anode might be bad pull off the prop it's screwed on with 2 screws behind the prop.

Re: Repairing lower unit surface

jason32038 said:

Your anode might be bad pull off the prop it's screwed on with 2 screws behind the prop.

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Wow...not to seem especially ignorant, but I had no idea about that. Considering the age, I would not be surprised it that was gone. I assume it's replacable?

Of note, the motor was in this condition when I inherited it...

So, what about the surface? What should I use to smooth it over?

Re: Repairing lower unit surface

Bondo is relatively soft and with age will wear away some. I am repairing similar damage with JB epoxy. After sanding the surface smooth and to bare metal, I will spray with expensive zinc chromate primer (14 bucks a can) and --oh, I don't know--maybe appliance white enamel. Whatever white paint I have available at the time, or whatever is on sale cheaply. I usually buy close-out paints from the auto stores for around 1-2 bucks a can.

I don't have any close-ups of the lower unit itself, but this engine was painted with the primer on the aluminum parts and covered with Dupli-Color acrylic auto paint bought on close-out for 2 bucks a can. --The decals were 75 though, and the orange trim was 6 bucks a can. Chrysler letters and front plate were salvaged from junkyard autos.

The anode is a circular zinc piece behind the prop. Remove the prop and you will see it. It is held to the case with two slotted screws and yes, you can buy a new one.

Re: Repairing lower unit surface

Frank Acampora said:

Bondo is relatively soft and with age will wear away some. I am repairing similar damage with JB epoxy. After sanding the surface smooth and to bare metal, I will spray with expensive zinc chromate primer (14 bucks a can) and --oh, I don't know--maybe appliance white enamel. Whatever white paint I have available at the time, or whatever is on sale cheaply. I usually buy close-out paints from the auto stores for around 1-2 bucks a can.

I don't have any close-ups of the lower unit itself, but this engine was painted with the primer on the aluminum parts and covered with Dupli-Color acrylic auto paint bought on close-out for 2 bucks a can. --The decals were 75 though, and the orange trim was 6 bucks a can. Chrysler letters and front plate were salvaged from junkyard autos.

The anode is a circular zinc piece behind the prop. Remove the prop and you will see it. It is held to the case with two slotted screws and yes, you can buy a new one.

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Wow, that looks sharp! I was planning on repainting the cowl as well. It has the original Force decals but they are old/faded/streaked....I thought about either finding the same decals for a stock look or using the wifes "Cricut" die cutter and my computer to make my own custom Force decal. I really like the orange trim. I hadn't thought about changing the color of that piece on mine but looking at yours, i think i will. Thanks for the info!

Re: Repairing lower unit surface

Frank Acampora said:

I usually buy close-out paints from the auto stores for around 1-2 bucks a can.

I don't have any close-ups of the lower unit itself, but this engine was painted with the primer on the aluminum parts and covered with Dupli-Color acrylic auto paint bought on close-out for 2 bucks a can.

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Sorry for the double post. If you get a chance to upload a pic(s) of the lower unit I would really like to see what it looks like with the paint job. And did you brush or spray?

Re: Repairing lower unit surface

Here are a couple more photos. Two are from an earlier engine and two are from the latest. I have included a before photo of the hood.

I did not refinish below the cavitation plate because on these lowers, they did not need it. However, on the one I am in process of doing, I have routed out ALL corrosion and have started to fill. I used a wire brush with a lot of pressure to get into every crevice on the gearcase torpedo.

You should use a wire brush on the torpedo and also on upper surfaces, but on the upper surfaces, after wire brushing, use a palm sander to remove oxidised paint and fair sound paint into the wire brushed areas. Deep pits will need to be filled before priming.

While brushing can provide satisfactory results, best finishes require spraying, between coat sanding, and multiple coats of primer and finish. However, on lower metal portions, only use one coat (the first) of zinc chromate because of cost.

Re: Repairing lower unit surface

Frank Acampora said:

Here are a couple more photos. Two are from an earlier engine and two are from the latest. I have included a before photo of the hood.

I did not refinish below the cavitation plate because on these lowers, they did not need it. However, on the one I am in process of doing, I have routed out ALL corrosion and have started to fill. I used a wire brush with a lot of pressure to get into every crevice on the gearcase torpedo.

You should use a wire brush on the torpedo and also on upper surfaces, but on the upper surfaces, after wire brushing, use a palm sander to remove oxidised paint and fair sound paint into the wire brushed areas. Deep pits will need to be filled before priming.

While brushing can provide satisfactory results, best finishes require spraying, between coat sanding, and multiple coats of primer and finish. However, on lower metal portions, only use one coat (the first) of zinc chromate because of cost.

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Just curious, how many boats do you have? In the one pic I notice another in the background.

Thanks for these pics! And the info. If mine looks half as good I will be happy. So the can of pain you're getting at the auto stores on clearance, are they regular cans or spray cans? And when you spray, is it recommended to cover the intake vents on the torpedo to prevent overspray from going inside, or is that not a concern?

Re: Repairing lower unit surface

Uhhh---I have mfxx, nydf, brppd--six boats and about twenty engines--lost count on the engines. One boat in photo, one in background, two in garage, one on the side of the house, and one in the back yard. They call to me like women. I try to keep all the boats blue and white so my wife would not notice when I brought home another. Photo is of the one on the side of the house.

Spray cans. When Dupli Color discontinues a color, it goes on sale and I buy as many as I can. It doesn't matter if the colors are slightly different because the first coats will be covered and the final coat only takes two matching cans. Around here, we also have a discount store called "Ollie's" They buy close-outs and sell them cheap. I picked up two cases of primer and a six pack of Dupli-Color Burgundy--at a buck a can. Now I just need to find a use for it.

Overspray in the water intakes will not harm anything. there is plenty of room behind them for water flow and nothing to be damaged.

Re: Repairing lower unit surface

Frank Acampora said:

Uhhh---I have --six boats and about twenty engines--lost count on the engines..

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wow... do you like fix up and sell or just collect them? lol

I will start looking paint for sail. I really like the colored trim on yours. I need to decide what color would be good for mine (boat in sig)...

Thank you for all the info! This will be a fun project!

Re: Repairing lower unit surface

If you have access to a sand blaster you might want to try that.
If not, drill, wirewheel(s) or flap wheel and some elbow grease.

I wouldn't suggest plain bondo. If you nick the paint it sucks up water like crazy. Instead made by the same company, get the fibergel bondo. It's tougher and resists water a little better. But prime, add fibergell, smooth, prime, paint and/or seal.

Hard to tell, but you may not even need to fill.