Treating Engine Surface Corrosion

Foswick

Foswick

.
Apr 25, 2024
305
Fuji 32 Bellingham
I have a low-hours Universal M-35B engine. The previous owner let a leak around the raw water pump go too long, and some surface corrosion developed around the area. It is not bad, but should not go unaddressed for too long. Engine compartment access isn't great, but fortunately, the corrosion is all on/near the front.

After cleaning and brushing off loose paint, what is the best way to treat the affected areas?
 
C

colemj

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Jul 13, 2004
448
Dolphin Catamaran Dolphin 460 Mystic, CT
If it's the cast iron block, then wire brush it, treat with phosphoric acid, and spray paint it.

Mark
 
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Stu Jackson

Stu Jackson

.
Feb 26, 2004
22,975
Catalina 34 224 Maple Bay, BC, Canada
If it is the aluminum gear housing cover, brush it and use appropriate aluminum primer and paint. Never use a steel brush. Also check and clean the engine mount, especially the rubber part; it may need replacing
 
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Rich Stidger

Rich Stidger

.
Feb 10, 2004
4,095
Hunter 40.5 Warwick, RI
I have had a similar situation with my engine. The raw water pump leaked and caused surface rusting. I wire-brushed it (brush material unknown) and then treated it with the POR-15 process. That is a de-greaser, cleaner/etcher, and the POR-15 coating. Then I painted with matching engine paint. 15 years later it still looks perfect. POR-15 is available from automotive painting supply stores. You only need a small amount.
 
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dLj

dLj

.
Mar 23, 2017
4,191
Belliure 41 Back in the Chesapeake
Rich Stidger said:
I have had a similar situation with my engine. The raw water pump leaked and caused surface rusting. I wire-brushed it (brush material unknown) and then treated it with the POR-15 process. That is a de-greaser, cleaner/etcher, and the POR-15 coating. Then I painted with matching engine paint. 15 years later it still looks perfect. POR-15 is available from automotive painting supply stores. You only need a small amount.
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This is a great system for ferrous based substrates, but if you have an aluminum substrate, I would not use it. The de-greaser is a potassium hydroxide based cleaner and I would not recommend that on aluminum.

dj
 
Foswick

Foswick

.
Apr 25, 2024
305
Fuji 32 Bellingham
It is cast iron. Do aluminum block marine diesels even exist?

The best picture I have, on-hand, is this low-res image from the sales listing last spring. I have since cleaned up the pulleys to prevent belt erosion. And, that rust on the far left looks deeper and more involved than it actually is. And, it looks like maybe there is some electrolysis making the paint bubble up in some areas. I haven't ruled that out, but the location of those areas makes me inclined to discount that diagnosis. (In general, this photo makes it look much worse than it actually is, but it is not negligible.

I think I'm going out to the boat for a few days this week and will be taking a deeper look at this.

The challenge I have is that most of the rust is settled into hard-to-reach spaces.

1744747630964.png
 
BigEasy

BigEasy

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Jun 21, 2004
2,761
Beneteau 343 Slidell, LA
That’s going to be difficult cleaning & brush all of the scale & if it isn’t pepped well, the paint will be compromised. Could you remove the rubber goods & tape, followed by hydroblasting/soda blasting, brushing & sanding remaining scale. Prime & paint.
 
Foswick

Foswick

.
Apr 25, 2024
305
Fuji 32 Bellingham
BigEasy said:
That’s going to be difficult cleaning & brush all of the scale & if it isn’t pepped well, the paint will be compromised. Could you remove the rubber goods & tape, followed by hydroblasting/soda blasting, brushing & sanding remaining scale. Prime & paint.
Click to expand
Well, I am resigned to the fact that the only way to do this properly would be to remove the engine. Access is just not great. And, I am not planning on removing the engine anytime soon. The Hobbs only shows about 500 hours, which I don't quite believe, but I do think it has fewer than 1000 hours and runs great.

So, unfortunately, I am just going for "good enough for a few years". Eventually, something will require me to pull the engine and I'll do a thorough restoration at that time.
 
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BigEasy

BigEasy

.
Jun 21, 2004
2,761
Beneteau 343 Slidell, LA
Foswick said:
Well, I am resigned to the fact that the only way to do this properly would be to remove the engine. Access is just not great. And, I am not planning on removing the engine anytime soon.
Click to expand
Agree! Too much involved to remove engine for paint'
 
C

colemj

.
Jul 13, 2004
448
Dolphin Catamaran Dolphin 460 Mystic, CT
Foswick said:
It is cast iron. Do aluminum block marine diesels even exist?
Click to expand
Yes. But the reason you were getting different answers without a picture is because many engines contain a mixture of aluminum and iron parts, and none of us knew where the corrosion was you wanted to solve.

That doesn't look bad at all to me.

Nothing special about Westerbeke paint except the price. Just get something close and you won't know the difference.

Mark
 
capta

capta

.
Jun 4, 2009
4,905
Pearson 530 Admiralty Bay, Bequia SVG
Foswick said:
It is cast iron. Do aluminum block marine diesels even exist?

The best picture I have, on-hand, is this low-res image from the sales listing last spring. I have since cleaned up the pulleys to prevent belt erosion. And, that rust on the far left looks deeper and more involved than it actually is. And, it looks like maybe there is some electrolysis making the paint bubble up in some areas. I haven't ruled that out, but the location of those areas makes me inclined to discount that diagnosis. (In general, this photo makes it look much worse than it actually is, but it is not negligible.

I think I'm going out to the boat for a few days this week and will be taking a deeper look at this.

The challenge I have is that most of the rust is settled into hard-to-reach spaces.
Click to expand
If you feel the need to get at that rust, you will probably need dental tools, tiny wire brushes, and small screwdrivers. After scratching, brushing and scraping off as much loose paint and loose rust as possible, saturate the area with Ospho, or phosphoric acid. Dry the area, spray with an engine primer and an engine (high temp paint) paint. If no more water is allowed to pool in there, your work should last years.
 
marcham

marcham

.
Jun 17, 2022
191
Hunter 380 Comox BC
Foswick said:
Well, I am resigned to the fact that the only way to do this properly would be to remove the engine. Access is just not great. And, I am not planning on removing the engine anytime soon. The Hobbs only shows about 500 hours, which I don't quite believe, but I do think it has fewer than 1000 hours and runs great.

So, unfortunately, I am just going for "good enough for a few years". Eventually, something will require me to pull the engine and I'll do a thorough restoration at that time.
Click to expand
That's what I was going to say.... I did an in-situe strip and repaint of my yanmar, but I only had a bit of rust below the heat exchanger..... took me two weeks. My back took a month to recover. Pull it, do it right. It's going to get worst very quickly and leaks will be tricky to identify.

Any corrosion underneath? On the oil pan? Oil pans for Universals can be tricky to find depending on the model...

Pulling a motor takes about 2 hrs.... easy peasy. Put it back in (install new mounts) then ask a mechanic to realign it.
 
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