Silicone on lower unit of an outboard

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djw2112

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Hi, i am replacing the waterpump of my outboard (1988 merc 115). Before replacing the lower unit back onto the engine it is common practice to place a bead of marine silicone between the water pump housing and the exhaust port.

Should i let the silicone dry first before replacing the lower unit? I have seen it done both ways (dry and wet) but i am concerned about which way is correct. It makes sense to let it dry first, but most videos i watch they leave it wet.

Does anyone know the best method?

Thanks
 

Tom

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Jan 13, 2005
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50,367
Hi, i am replacing the waterpump of my outboard (1988 merc 115). Before replacing the lower unit back onto the engine it is common practice to place a bead of marine silicone between the water pump housing and the exhaust port.

Should i let the silicone dry first before replacing the lower unit? I have seen it done both ways (dry and wet) but i am concerned about which way is correct. It makes sense to let it dry first, but most videos i watch they leave it wet.

Does anyone know the best method?

Thanks
Some manufacturers say their product can be applied underwater, so I wouldn't worry about cure time on those. Others, such as the well known 3M 5200, specifically state a minimum cure time before going back in the water (48 hours in the case of 5200). I'd follow the manufacturer's instructions.
 

djw2112

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Thanks Tom :) But i may not have done very well in explaining what i was asking, sorry about that :)

Im wondering if i put the lower back while the silicone is squishy or after it is fully dried. It wont be going in the water till next season 4 mos away. Some people assemble the lower while the silicone is still soft, some people assemble the lower after that bead has fully dried.

So one way the silicone is soft and takes the shape of the apposing side and then dries when you bolt it together, and the other way the silicone has dried already and that bead will keep its shape thick shape and just press against the apposing side.

I hope i explained that better. :)
 

Tom

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Im wondering if i put the lower back while the silicone is squishy or after it is fully dried. It wont be going in the water till next season 4 mos away. :)
Sorry, I misread &/or misunderstood what you were asking. I'd be inclined to put it together while the silicone is squishy, but I suspect others might have a different opinion. Apologies if that doesn't help :(
 

SpencerPJ

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Midwest
I'll second Tom, but I let it to setup slightly then assemble. I wouldn't let it cure fully then assemble.
 

Boat Bum

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Ask your question here for answers from professionals. They are a nice group of helpful folks.

 

djw2112

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East Texas
Thanks for the tips and the link :) I am a member of another boat forum but i rarely get answers, and when i do its a month or so late. I will register on that forum.
 

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