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Powerhead back on... sealer???

Grumpy Bear

Grumpy Bear

Regular Contributor
About to put the rebuilt powerhead back on the main housing on my 74' 50hp Thunderbolt 500. There is a gasket between the powerhead and exhaust extension plate assembly as well as a gasket between that plate and the top of the lower unit. Should there be any sealant on these gaskets or go on dry? Thus far, the only goop I've added is the metal-to-metal of the crank cover to the cylinder block (Permatex aerial gasket maker). The rest of the gaskets have gone on dry on well-cleaned surfaces.
 
Goop is not needed, and it's a bear to clean off when the next person (you?) tries to get it off.

Many people put anti-seize on the gasket to prevent this; others go with silicone ONLY--no gasket. Both approaches work fine.

Jeff
 
fastjeff said:
Goop is not needed, and it's a bear to clean off when the next person (you?) tries to get it off.

Many people put anti-seize on the gasket to prevent this; others go with silicone ONLY--no gasket. Both approaches work fine.

Jeff
Click to expand...

Thanks, Jeff. Now I just need to figure out how to remove the throttle/shift cables from the exhaust extension plate (and get them back on right!). Any tips on doing that?
 
Think of it this way: For decades now every auto engine on earth is assembled with silicone instead of gaskets (head gaskets excepted).

Jeff
 
I prefer the clear--it doesn't look so bad when it oozes out.

Jeff

PS: There ARE cases when both are needed: the cylinder head water jacket, for example. Just lately I had one that refused to stop leaking around the plugs until I double gasketed it in that area alone, along with silicone.
 
fastjeff said:
I prefer the clear--it doesn't look so bad when it oozes out.

Jeff

PS: There ARE cases when both are needed: the cylinder head water jacket, for example. Just lately I had one that refused to stop leaking around the plugs until I double gasketed it in that area alone, along with silicone.
Click to expand...

I've got some Permatex RTV Red. Maybe a thin coat on each side of the gaskets wouldn't hurt.... When I was removing the gasket from the mating surface of the lower unit housing and the underside of the exhaust extension plate, there was something Mercury coated it with -- looked yellowish-green and felt like epoxy of some kind.
 
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If exhaust plate and powerhead surfaces are clean put it together dry,the only place Mercury call for use of silicon is on the lower units(bigger models). If you use the newer Merc gaskets they are greenish and are silicon impregnated and seal with heat. If your just dying to use some make sure its a very thin coat...If I was going to use something it would be the "peanut butter" gasket sealer over silicon.
 
faztbullet said:
If exhaust plate and powerhead surfaces are clean put it together dry,the only place Mercury call for use of silicon is on the lower units(bigger models). If you use the newer Merc gaskets they are greenish and are silicon impregnated and seal with heat. If your just dying to use some make sure its a very thin coat...If I was going to use something it would be the "peanut butter" gasket sealer over silicon.
Click to expand...

Not "dying" to use silicone, jeez. Just wanting to minimize the possibility of leaking. One gasket (under the exhaust plate extension) is black. That's the one that seemed to have something coated on the meeting surface under it. The gasket on the top of the exhaust plate is green as you describe. Also noticed the surface on the top side of the exhaust plate where water comes up and into the cooling system has a little ridge running around the middle of that part of the surface. I assume that's to ensure a better seal on the gasket?? Just curious.
 
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Just wanting to minimize the possibility of leaking
Click to expand...
If its clean and dry it wont leak, make sure the pull the bolts down in a cross pattern.....and I have never had one leak doing this.

6....7
1....2
3....4
8....5
 
faztbullet said:
If its clean and dry it wont leak, make sure the pull the bolts down in a cross pattern.....and I have never had one leak doing this.

6....7
1....2
3....4
8....5
Click to expand...

Good words. I did indeed tighten in the inside-to-outside and cross pattern (and torqued to spec) on everything on the powerhead. Just to clarify, I was specifically talking about putting the powerhead back on motor. The first pic below was where I took the black gasket off under the exhaust extension plate. It had some kind of epoxy or coating on the aluminum (or steel?) meeting surface. That's the one I was asking about putting some kind of sealer with the black gasket. The second picture is the exhaust extension plate. The red is circling the part that meets up with where the water goes up into the powerhead to cool. I was just wondering why the surface has a little ridge through the middle of it. (This gasket is a green one, by the way).

gasket1.jpgridge.jpg
 
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