Paint for motor mounts

R

Rjm st.petersburg

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Jan 5, 2021
159
Hunter 41 DS Saint Petersburg
I had a lag screw shear off where the shoulder meets the thread in my motor mount. I have not been able to extract it out of the stringer. So this is my plan B. I welded an additional piece of metal onto my new motor mount and plan on driving a new lag screw into the stringer and abandoning what's left of the old one, sealing it in an epoxy tomb. I am replacing all 4 mounts and using new lag screws. Yanmar 4jh4e, 2005 in a 41 Hunter DS.
What paint would be best to protect this bare steel as well as the rest of the metal part of the new motor mount?
Robin
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,150
Hunter 310 West Vancouver, B.C.
Excellent solution.

The only thing I might add at this point is that the stringer at this point is solid wood to accept he lag bolt. The new lag bolt is very close to the original lag bolt hole and I would be concerned about splitting the wood seeing as they will likely occupy he same section of wood grain between summer and winter growth. The only solution that comes to mind right now is to make the extension much longer. This shouldn't affect the ability to do an alignment as you do not want to twist the mount, just move it from side to side.

As far as paint goes, rough up the metal with ≈240 grit emery paper and primer and paint with epoxy paint if you want to go bat-:poop: crazy for corrosion prevention. If it were me, I'd use Rustoleum spray can products. But far more important than the paint, is to ensure there are no sea water leaks above the engine supports. I got caught with this problem about 10 years after I bought the boat new where I had a corrosion problem which was not in plain view. I replaced the one mount just out an abundance of caution and it seemed like an interesting project over the winter.

1678462571935.png
 
dLj

dLj

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Mar 23, 2017
4,214
Belliure 41 Back in the Chesapeake
Is that motor mount an OEM or after market part?

Neither the bolt nor the mount appear to be corrosion resistant materials.

If that's a carbon steel plate, i would buy cold galvanizing spray paint and paint with that first. I run multiple coats. Then paint with a good epoxy.

Just a FYI, I would not want that motor mount in my boat if indeed that's plain carbon steel.

dj
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,150
Hunter 310 West Vancouver, B.C.
dLj said:
Just a FYI, I would not want that motor mount in my boat if indeed that's plain carbon steel.
Click to expand
They're ALL carbon steel. The same as most other mechanical fitting on the exterior of your engine. Bolts, brackets, mountings, pulleys ? All carbon steel. Run a magnet over your engine some time looking for anything that is NOT magnetic. No need for any other material as they're not intended to be in water. Just watch out for sea water leaks around motor mounts.
 
R

Rjm st.petersburg

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Jan 5, 2021
159
Hunter 41 DS Saint Petersburg
They are Yanmar OEM mounts. They are very proud of these mounts. I was thinking of an epoxy paint, or cold galvanize spray. I didn't think the epoxy paint would adhere to the cold galvanize which is why I posted here. I have 150 mounts on port, and 200 on starboard. I was planning on a brass brushing then paint everything I could except the rubber and adjustment bolts. At this point the cost of paint is inconsequential.
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,744
Hunter 430 Waveland, MS
C

Calif. Ted

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Jun 8, 2004
2,926
Catalina 320 Dana Point
I use Rustoleum gloss black and primer, I've only tried the cold galvanizing spray on an anchor and it didn't work at all well there.engine.jpg
 
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R

Rjm st.petersburg

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Jan 5, 2021
159
Hunter 41 DS Saint Petersburg
No brass fittings, I was going to use a brass BRUSH in place of Emory cloth. This is not going to be submerged as an anchor would. If the epoxy paint will adhere to the cold galvanize, wouldn't that be the way to go?
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,150
Hunter 310 West Vancouver, B.C.
Rjm st.petersburg said:
If the epoxy paint will adhere to the cold galvanize, wouldn't that be the way to go?
Click to expand
Cold galvanizing is the weak ling in the chain. The epoxy will separate from the sprayed on zinc. Epoxy relies on a tight grip to the base metal.

This is one of my three Yanmar 24 year old motor mounts in a picture taken recently:

1678467869260.png


Zero corrosion on all mounts.
Keeping it dry = 0 corrosion
 
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R

Rjm st.petersburg

.
Jan 5, 2021
159
Hunter 41 DS Saint Petersburg
I've owned the boat 2 years. There was minimal maintenance history, so I guessed these have never been changed since new in 2005. The old mounts only had a little surface rust as depicted in Ralph's photo. However the rubber seemed very hard. I am guessing that is what caused the lag bolt to shear off. I could see corrosion at the break on the shoulder of the lag with the exception of just a small amount that was apparently holding it together. So this has been compromised for awhile and finally gave it's last breath.
Sounds like I should skip the cold galvanize and go with the epoxy paint. They will stay dry, no problem with that. As long as I am treating the bare metal with paint, I was thinking of painting the rest of the metal surfaces on all of the new mounts.
Robin
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,744
Hunter 430 Waveland, MS
Rjm st.petersburg said:
I'm also planning on using aluminum to replace the plastic star board shims.
Click to expand
Listen to @Ralph Johnstone about corrosion [and me].

Aluminum will work ok.

You should avoid mixing metals on your boat, but when you can't do that, use this to coat the metal interface.

V4A9298-LOW.jpg

No water on metal = zero corrosion.

Epoxy paints are not a cure.
Jim...
 
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dLj

dLj

.
Mar 23, 2017
4,214
Belliure 41 Back in the Chesapeake
Ralph Johnstone said:
They're ALL carbon steel. The same as most other mechanical fitting on the exterior of your engine. Bolts, brackets, mountings, pulleys ? All carbon steel. Run a magnet over your engine some time looking for anything that is NOT magnetic. No need for any other material as they're not intended to be in water. Just watch out for sea water leaks around motor mounts.
Click to expand
Ha, i hadn't realized that.

Back when we were making our own motor mounts we never used plain carbon steel.... But custom and off the shelf aren't comparable....

Looking at my current motor mounts they sure are carbon steel... I'm adding in a new maintenance step...

dj
 
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