Topic: Surface Condition Base Gasket – Antique Outboard Motor Club,Inc

This topic has 9 replies, 8 voices, and was last updated 1 month ago by aquasonic.

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October 16, 2024 at 5:50 pm #291568
Buster
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US Member
I’ve completed the water pump installation on my 1955 Johnson CD-12. My question is about the required cleanliness of the base gasket surfaces. The old gasket came off in chunks with lots of gasket remaining. I’ve used a combination of gentle scraping, bronze bush, and Scotch-Brite. The surfaces are pretty clean but not spotless. Do I need to have both surfaces clean to a bare metal appearance or is some remnant of old gasket (or sealer) acceptable? I’ve got a new OEM gasket to install, which I’ll coat with OMC Triple Guard grease.

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Sputter
October 16, 2024 at 7:11 pm #291571
Gary H.
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It looks pretty clean but it could be cleaned more thoroughly in my opinion. I would first use some mineral spirits or denatured alcohol with the scotch brite pad and clean it a little more noting not to sand it and create low spots. Then I will usually take a single edge razor blade at this point and back drag it across the surface several times to clean it up. If you have an area that still has some gasket left on it, use the razor blade very gently in a forward direction to clean it off and then back drag it again. The goal is to not create any deep scratches or gouges. Finish by wiping clean with either of the solvents on a clean rag. This is my process and I am sure others will other options for you. Best of luck on your repair.
October 16, 2024 at 7:15 pm #291572
labrador-guy
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Buster I use a razor blade scraper to clean both surfaces when I remove a power head. You don’t want that gasket to leak water that comes up from the impeller. A clean flat surfaces are always the best thing.

dale
October 17, 2024 at 12:02 pm #291588
The Boat House
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Paint stripper (Aircraft – Klean Strip – Super Strip – ect.) can help in removing gasket material without damaging the sealing surface. Tubs
October 19, 2024 at 6:39 am #291618
aquasonic
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The Boat House wrote:

Paint stripper (Aircraft – Klean Strip – Super Strip – ect.) can help in removing gasket material without damaging the sealing surface. Tubs

Paint stripper works for the most stubborn remains of the old gasket. For the mechanical removal a plastic razor blade scraper followed by a brass brush with WD-40. All remains of the old gasket and sealant need to be removed. Staining is normal and ok.

I also use OMC Triple Guard grease on the base gasket and mating surfaces. This works as long as the surfaces are smooth and clean. The next time you pull the powerhead for servicing, it will separate nice and easy plus you can reuse what has become a very expensive gasket for the 1954 and 1955 OMC motors.

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Sputter
October 19, 2024 at 9:45 am #291625
Sputter
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US Member
Would you use the same technique for a head gasket?

I had some stubborn bits of gasket that just wouldn’t budge. I put 1200 grit wet/dry sandpaper on a glass plate and did some gentle figure 8s.

It worked well for the head, but I don’t want to risk grit on the block.

I’ve tried the plastic razor blades and the brass brush, but there are spots where I can feel a small amount of old gasket with my fingernail.

1956 Johnson 15 Hp, FD-10
1958 Johnson 5.5 Hp, CD-15
October 19, 2024 at 10:14 am #291626
The Boat House
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It can take some time as the paint stripper needs to be absorbed by the remaining gasket material so it can reach, and soften, the bond at the surface. Repeated applications may be necessary to “help in removing gasket material “. It’s not very effective in dissolving carbon. Depending on the material & the location, it may not work 100%, but my experience is it’s been worth the effort. Tubs
October 19, 2024 at 10:28 am #291627
crosbyman
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Canada Member - 2 Years
I have used those small square paint scrapper blades used for cleaning up windows aftera paint job. At the proper angle they seem to pick up anything your fingernail will. same for a well sharpened wood chisel held at a small angle to prevent any gouging.

any gouges can be levelled with some JB weld high temp. steel epoxy.

Joining AOMCI has priviledges 🙂
October 20, 2024 at 7:11 am #291640
outboardnut
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US Member
this is what I use-
Dremel EZ471SA EZ Lock Detail Abrasive Brush
https://www.dremel.com/us/en/p/ez471sa-2615e471aa?srsltid=AfmBOoodjeRN_vLR9J31WvLgo5C57uoSd79V3fkABQuUa1vTNnW5-ROB
October 20, 2024 at 12:25 pm #291644
aquasonic
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US Member
outboardnut wrote:

this is what I use-
Dremel EZ471SA EZ Lock Detail Abrasive Brush
https://www.dremel.com/us/en/p/ez471sa-2615e471aa?srsltid=AfmBOoodjeRN_vLR9J31WvLgo5C57uoSd79V3fkABQuUa1vTNnW5-ROB

I have a Dremel and this looks worth trying. Thank you outboardnut.
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