Bravo 3 Transom Assembly
 

What's the general consensus on the transom assembly seal when it comes to needing sealant? I've seen comments from dry or needing a coat of grease to needing 4200. I know 4200 wouldn't hurt, but is it really necessary? The transom is in excellent condition and flat. The assembly is new Mercruiser.

Buddy had one done a couple years ago. Factory put original in dry and it was still good with no signs of leaking after 15 years. New assembly/gasket was put back on same way. Like your boat his transom was nice and flat.

The only thing that has me wondering is the material the gaskets are made of. The one I removed seems to be rubber where the new one is foam. I coated it with grease, but now I'm second guessing before I put the motor back in whether I should use 4200 sealant.

Put it on dry

Grease is not good and can cause the seal to break down depending on what the gasket is made of.

I already applied a little grease and installed the assembly. The gasket is foam like a cars trunk gasket.

I installed dry in 2018 and no leaks since.

Remove, clean with dawn dish soap

Agree it appears to be like a truck gasket, but I also installed new and dry some years back

Never put a thing on one. Grease/gas/oil breaks down rubber.

Agreed grease is a bad choice. What is the benefit?

I did mine a few years ago, and added a very thin film of silicone to the edges of the assembly (not on the seal itself).

What about marine lithium grease? It's not the same as regular petroleum wheel bearing grease. Just trying to figure out if it's really necessary to pull it back off. Thanks.

Edit: I think I answered my own question. It's still petroleum based so I guess I'm pulling it off. Thanks for all the responses guys.
Last thing... fwiw, the new seals aren't really rubber, but a foam like seal it seems like.

3M Marine sealant 101
A long lasting waterproof seal without any unwanted bonding strength when you have to disassemble things later , unlike other sealants.
NO silicons to interfere with future paint work or glass repairs.
I've used it on all my I/O transom assemblies and strongly recommend it for any outboard mounting holes through the transom as well.
I use it for bedding deck and through hull hardware also.

Thanks allot for the suggestion. I'm assuming you're talking 4200 right? Looks like that's a pretty common product that guys like to use.

If I had meant 4200 I would have said 4200 .. :lolhit:

Check out the 3m web page 3m 101 sealant .

At the risk of sounding like a broken record there are many other types of sealants available than just 5200 and 4200

Chill buddy. I missed the 101 part. When I googled it all that came up was 4200 and 5200. I'll take another look. Thanks.

Edit: 101 is no longer available.

Check out the Boatlife range of sealants .They make 2 polysulfide type sealants equivalent to the 3M 101 . One is siliconized and the other isn't .
Incidentally , I think it's a good idea to do an additional seal on the transom plate . I'm sure any mechanics who have been around long enough have stories of many factory gaskets that have failed after time causing many a rotted transom .

I'll probably go with the Life-Calk only because I did put grease on the seal initially. I'll clean it with a little Dawn first.

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Looks good man!!! Was gonna suggest some penetrating epoxy on the cut out...but too late!!! Throw the engine in and outdrive on and go boating!!!!

Thanks. Not too late yet though. I'm pulling it back out to put the sealer on. Haven't done it yet. Five minutes worth of work to pull it. I might pick up some paint too. We'll see. The paint is in pretty good condition still.
It'll be a little bit before I put the motor in. I dropped the block off at the machine shop to have a couple things done.

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While its out sand some of the bottom paint away. Bottom paint should not contact the transom assembly, and most leave 1 inch space.

I think you'll be pleased in the long run .
One of the nice things about the lifecaulk is that it's very easy to trim away the excess . I often use a wooden chopstick (like the ones that takeout Chinese food come with) and sharpen the tip up a bit .

There isn't any bottom paint near the sealing surface. It was painted with the old assembly installed so it won't touch the new assembly.

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