aluminum/brass reaction?

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aluminum/brass reaction? mark 04-05-2006
Posted by mark on April 5, 2006, 2:20 pm
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 I would like to tap a barbed fitting into the aluminum gearcase of my
outboard motor. I cannot find stainless barbed fittings and I assume brass
and aluminum touching under salt water is a no- no. If I tap the aluminum to
take a stainless 1/4" bushing and then thread in a 1/8" barbed brass fitting
will there still be corrosion problems. There are several zinc anodes on the
motor and aluminum hull.



Posted by Ken Davey on April 5, 2006, 3:00 pm
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 mark wrote:
> I would like to tap a barbed fitting into the aluminum gearcase of my
> outboard motor. I cannot find stainless barbed fittings and I assume
> brass and aluminum touching under salt water is a no- no. If I tap
> the aluminum to take a stainless 1/4" bushing and then thread in a
> 1/8" barbed brass fitting will there still be corrosion problems.
> There are several zinc anodes on the motor and aluminum hull.


Umm - first question - why?
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Posted by Ned Simmons on April 5, 2006, 3:05 pm
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mark@islandtelecom.com says...
> I would like to tap a barbed fitting into the aluminum gearcase of my
> outboard motor. I cannot find stainless barbed fittings and I assume brass
> and aluminum touching under salt water is a no- no. If I tap the aluminum to
> take a stainless 1/4" bushing and then thread in a 1/8" barbed brass fitting
> will there still be corrosion problems. There are several zinc anodes on the
> motor and aluminum hull.
>

You're correct that brass will be worse than stainless, but SS barbs are
available. See McMaster pp.240 & 245 for examples. A tough plastic would
be safest from corrosion - McM has a lot of plastic barbs and
compression fittings as well.

Ned Simmons

Posted by Don Foreman on April 5, 2006, 5:07 pm
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wrote:

>I would like to tap a barbed fitting into the aluminum gearcase of my
>outboard motor. I cannot find stainless barbed fittings and I assume brass
>and aluminum touching under salt water is a no- no. If I tap the aluminum to
>take a stainless 1/4" bushing and then thread in a 1/8" barbed brass fitting
>will there still be corrosion problems. There are several zinc anodes on the
>motor and aluminum hull.

Stainless and aluminum are also not good together. The zinc anodes
won't help much if they're very far from the joint because the local
return path for current is much shorter (hence lower resistance) than
the path from the Zn anode.

A strong plastic fitting would be best. It would be best to make
your own, using a relatively small thru-hole to get plenty of wall
thickness. That could be a bushing or adaptor; then the barb (more
moment on long barb) could be made of brass.

I would make an aluminum barbed fitting and then hard- anodize it.
Anodizing will keep the threads from galling, and presents an
electrically non-conductive surface. Probably more screwing around
than you want to do.
>

Posted by az_100 on April 6, 2006, 4:44 am
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I have fitted a brass barbed fitting to my outboard's leg. It is higher
up though, where the exhaust relief port is located. My outboard is in
a semi closed well and this port would fill the well with smoke and
starve the motor of air.
The barb has a hose fitted which leads the fumes out the transom via
another ( plastic) barb.
There are no corrosion problems after about 6 years use, mainly because
the barb gets well oiled from the two stroke exhaust.
Klaus


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