MC-1 transom + cork gasket, to seal or not to seal?

[ttownthomas]

I have finally gotten to a re-assembly point after removing the rotted core and replacing with Coosa on my 1972 Bertram 25 with Mercruiser 165 L6's.

I have rebuilt transom assemblies and I am getting ready to re-install them. The rebuilder that sold me the transom assemblies included tubes of 3M 5200 along with the appropriate cork gaskets BUT I have read here that the cork should go on dry or with just a dab of gasket adhesive.

The transom is freshly painted and awfully clean, flat and smooth.

My instinct is to use 4200 or nothing but is there any "new" conventional wisdom? Most of the threads on this topic I found were at least 10 years old.

 

[ttownthomas]

I Found a picture of the transom too:

 

[Bondo]

Ayuh,.... Sealant shouldn't be needed, but if it allows ya to sleep better at night, go ahead, 'n seal it,....

 

[ttownthomas]

Yeah, not sure I should use any sealant if its torqued right....But if I do is there a downside to using 4200?

 

[Scott06]

Yeah, not sure I should use any sealant if its torqued right....But if I do is there a downside to using 4200?

You may have trouble getting the housing off if you ever need to

 

[kenny nunez]

Sealant may cause the gasket to split. You could go around the perimeter of the transom plates after they are torqued down.
Nice fiberglass job I must say.

 

[ttownthomas]

Sealant may cause the gasket to split. You could go around the perimeter of the transom plates after they are torqued down.
Nice fiberglass job I must say.

OK, No sealant. The boat will not be stored in the water anyway.

Thanks for the fiberglass comment!

 

[ttownthomas]

So, it looks like the transom bolts/nuts only get torqued to 20-25 pounds...?

 

[ttownthomas]

So, it looks like the transom bolts/nuts only get torqued to 20-25 pounds...?

One more question: Do I seal the bolt holes? Or leave them dry too?

 

[kenny nunez]

If the insides of the mounting holes are not sealed you could put a ring of sealer around the studs where they protrude inside the transom before bolting the inner mounting plate in place.
That will keep moisture out of the holes from the inside.

 

[markhodges78]

One more question: Do I seal the bolt holes? Or leave them dry too?

No need to use sealer as the transom seal seals water from getting to the bolt holes as well. If water does make it thru the transom seal then it would come in the giant hole in the transom and not the bolt holes..

 

[nola mike]

One more question: Do I seal the bolt holes? Or leave them dry too?

I filled with 4200 before installing the bolts. Looked like a vulnerable area. My bolts were severely corroded with some surrounding transom rot. I cleaned the transom area, filled with resin/PB, redrilled first. In retrospect just the 4200 probably would have been enough to fill the void, as you're dealing with a relatively low clamping force over a large surface area.

 

[nola mike]

No need to use sealer as the transom seal seals water from getting to the bolt holes as well. If water does make it thru the transom seal then it would come in the giant hole in the transom and not the bolt holes..

Disagree. Water can definitely enter through the bolt holes. Same as any transom penetration. See my above comment.

 

[markhodges78]

Disagree. Water can definitely enter through the bolt holes. Same as any transom penetration. See my above comment.

How? If water is getting into the area of the transom mount bolts then that means it's getting past the seal on the transom mount does it not ?

 

[markhodges78]

Are the bolts not on the inside of the sealing area

 

[nola mike]

Are the bolts not on the inside of the sealing area
View attachment 371056

Thinking the intrusion is from the outside in. There's a little rubber washer iirc

 

[Bondo]

Are the bolts not on the inside of the sealing area
View attachment 371056

Ayuh,...... They are,.....

 

[markhodges78]

Ayuh,...... They are,.....

That's the way I took it as well. So one would say no sealer needed on the mounting bolts correct? Am I wrong in thinking that if water can make it to the mounting bolts that there's a penetration for water to enter much larger then the bolt holes

 

[nola mike]

Not sure why you guys don't think that water can get to these bolts. They are exposed to water and sealed with a rubber oring. My bolts were severely corroded, and water had rotted the area around the bolts.

 

[markhodges78]

Not sure why you guys don't think that water can get to these bolts. They are exposed to water and sealed with a rubber oring. My bolts were severely corroded, and water had rotted the area around the bolts.
View attachment 371102

Ok I can see using sealer on the bottom 2 bolts for extra measures but if you expect the o-ring seals to leak then you should also expect the transom seal to leak