dtbushpilot - 3-24-2013 at 08:18 PM
I'm finally getting around to doing the stuff that I've been putting off to get my boat back in the water for fishing season. I noticed some of the
paint on the outdrive was coming off and upon further examination found there to be some significant corrosion going on. I'm not really losing any
material to speak of but I need to get it cleaned up and re-epoxied.
There is a lot more involvement than what is shown in these pictures. I have scrapped away the paint but now need to find something to neutralize
and/or remove the white powder. I can scrape at it and sand it off but it is still in the pores of the aluminum.
I want to do the best that I can with it without taking it apart so I need something to clean it with that won't damage the rubber boots and hydraulic
lines.
Any suggestions?
sorry for the poor photo quality, taken too close with my cell phone.
[Edited on 3-25-2013 by dtbushpilot]
[Edited on 3-25-2013 by dtbushpilot]
Terry28 - 3-24-2013 at 08:55 PM
You might try muratic acid..I know it's misspelled...but it the also used in swimming pools...nasty stuff but very effective. Consider a 50% solution
first, then full strength if that fails.
Bomberro - 3-25-2013 at 06:52 AM
I/O's sometimes take a lot of work to maintain in Baja's high salt sea. You might want to check the anode between the prop and housing, make sure its
making good contact with the aluminum, the anode on the bottom of the transom shield needs to be checked also, sometimes paint or other things may
block the current flow into the zinc. Sometimes the bottom paint does not have the one inch space around the transom shield and thus conducts a
current flow to the outdrive. Last time our bottom paint was redone they painted right up to the shield, took better part of a day to scrub and sand
it away with lacquer thinner. Good luck and good fishing.
larryC - 3-25-2013 at 08:15 AM
Ditto what Bomberro said. And you might want to think about adding another anode to the hull and bonding it to the engine and outdrive.
Larry
PS Not sure what to do about the existing corrosion but the muriatic acid idea is probably good and then some zinc chromate primer and last a good
paint for aluminum.
Pompano - 3-25-2013 at 08:30 AM
Good answers to an age-old problem...saltwater v.s boat.
Using the m/acid is a good way to tackle a problem that has progressed to the nasty stage. (Let's hope you don't have to resort to blasting. If so,
try to use walnut chips.)
You know all about proper maintenance, periodic scrubbing, etc. Here's something to make those zinc problems easier to solve. I've had both direct
drive and I/O's and this is a great tool for checking zincs, corrosion, etc.
http://www.boatzincs.com/corrosion-reference-electrode-specs...
Good luck and Good Boating.
BOAT = Break Out Another Thousand. 
edited to add my old shaft drive diesel...a love affair topside, but a war underneath!
[Edited on 3-25-2013 by Pompano]
dtbushpilot - 3-25-2013 at 10:35 AM
I'm beginning to think that it has to be an electrolysis issue, the section that the exhaust bellows attaches to (under the fork in the lower picture)
is also involved from where the bellows attaches about 1/4 of the way back. The fork doesn't have a zinc nor does it have a grounding wire but the
lower section has a zinc. Both zincs are heavily corroded and I will be replacing them.
Thanks all for the advice......dt
DavidE - 3-25-2013 at 11:03 AM
dtbushpilot X 2
Zincs, zincs, and more zincs!
A truly awful suggestion.... 
"Copper pennies" are copper plated zinc discs. And a roll of 50 of them is plenty cheap. Just sayin'