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View Full Version : Corrosion is killing me!



Surfer
08-30-2005, 07:47 AM
Last year I sand blasted, zink crome/primer/Awl griped the entire drive, rebuilt all (new zinks) and it looked bullit proof. Last week I ran it pretty hard, and the paint on the shift linkage cover ripped off (Volvo 280), exposing about 1/8" of white corrosion that had grown under the paint. The rest of the drive is solid. Why just the linkage cover and nowhere else? Any thoughts?

Morgan's Cloud
08-30-2005, 09:29 AM
Awlgrip has a line of prep materials including primers specifically for aluminium/alloys when using their system. Did you use them (out of curiousity) ?

Maybe everything on the unit is 'grounded' except the shift linkage cover..

Just a thought .. for whatever it's worth :biggrin:

Steve

MOP
08-30-2005, 12:54 PM
I have done a lot of aluminum painting, one thing I was taught was as soon as you thouroughly clean the surface it must be immediately wiped down with MEK or Acetone and primed. Aluminum oxidizes rapidly after being abraded moisture in the air and contaminants on your hands will effect the surface. On drives I made it a habit of applying two good even coats and letting it sit for at least 3 days to insure that no festering appeared, the slightest bit will magnify ten fold under paint. Every last spec of the surface must be super clean and bright, the slightest spec of discoloration will spell trouble.

Phil

Surfer
09-01-2005, 08:13 AM
I actually did use "alluma prep" an Awl Grip product on the case, and the zinc chrome on the metal (linkage ect) as I said the majority of the drive looks great, no blisters. Just the removable case, which I guess I totally lifted from ground by insulating it. How do I make that connection without exposing metal?

Morgan's Cloud
09-01-2005, 08:38 AM
I don't know for sure if the cover plate HAS to be grounded or not .. it was just an idea.... besides, it sounds more like you are talking about regular corrosion as opposed to electrolysis.
If that's the case , like Phil said , prep is critical and you may have left a finger print or another microscopic flaw in that spot .. otherwise look for a fracture in the paint that would allow the water to creep under it . At least it's just the cover and not some PITA place on the lower unit huh ?

Steve

Surfer
09-01-2005, 02:29 PM
In regard to metals, what is the differance between Electroylisis and corrosion? The stuff under the paint on the linkage cover was a whiteish powder on top of pitted metal.

AVickers
09-01-2005, 02:50 PM
Is the boat kept in the water? Is it salty or brackish?

If so, the whole thing (water and boat metal) is like a battery and a slight electric current will flow through the system with electrons moving from metal into the water. The zinc is designed to be the sacrifical element -- easily giving its electrons up to the water in lieu of your aluminum, iron, steel or bronze parts. To be effective, an electrical connection must be maintained between all components being protected (anything in the water). The screws holding the cover on should provide this unless the paint/primer in the hole serves as an insulator. When painting the cover, tape off the bottom of the screwhole so the stainless screw will make an electrical contact with the aluminum cover. This should minimize electrolysis on the cover.

Surfer
09-01-2005, 03:15 PM
Thanks, that makes perfect sense, so I would guess my problem is electrolysis. The boat is always trailered, and covered. I do run it a couple times a week though, and always in the salt. The screw holes were definitly paint filled.