Will Galvonic Corrosion be an issue? brass into aluminum (Volvo SX Gimbal bearing)

[Craig W]

Considering some challenges that came to light on another thread (I've cross linked for anyone searching http://forums.iboats.com/showthread....86#post3099486 ) I'm lead to Another Question that maybe Don S, Bondo, other guru's, any metallurgists amongst the forumship might be able to help with...

Since my "extension tube" pulled out which can/might lead to a leak if I put the old one back in, and I'm not inclined to replace it with a new VP tube (which potentially may also leak) I'm considering a retrofit/modification to the design. My intensions are to thread the Gimbal bearing housing similar to that in the FAQ, and then create a metal tube with an 1/8"NPT thread on the end to thread into the gimbal housing and then tap the opposite end for the zerk. Replacing the press fit plastic tube with a threaded metal tube instead of just putting the zerk inside the housing per the FAQ. As the housing is aluminum, will a dissimilar metal create a galvanic issue? If I use brass (which I have on hand) or stainless (which I'd have to buy) work? Both of them are more noble than aluminum and therefore the aluminum would be sacraficial, should galvanic corrosion take place... would the zinc anode on the outdrive protect from the tube's connection? Or is it to far "removed" to protect from this direct a connection? Should I consider sourcing and using an aluminum tube? Considering the zerk fittings are coated steel, would they not create a problem on their own just connecting to aluminum? Is that why Volvo might have opted to use this stupid plastic tube pressed into aluminum, to remove any possible bonding? Am I over thinking this? Any insight, thoughts?

[Don S]

There are already several stainless studs and bolts in the transom shield and outdrive, I doubt that a small piece of tubing will cause any problems. But I would look very closely to make sure the increased size of the pipe will actually fit in the area of the transom shield where the hole is.
One thing, once the zirk was installed in the drive as in the link, a straight tube on a grease gun got to it very easily by just turning the drive to port for some extra room.

[Craig W]

Thanks for the reply Don.

Reading the gimbal bearing/zerk FAQ I hadn't realized that the fitting would be so easily accessible. I just turned the drive hard to port and... Well, I will be going with the KISS theory! (abandoning my above idea and just tapping out the housing for a zerk!) no need to re-invent a remedy that will function so well.

...maybe you could add a comment into the FAQ identifiying that the fitting will be easily accessible when the drive is turned to port? just in case there's anyone else out there that (like I did) has the odd brain-fart and doesn't see the bigger picture ;-)