Corrosion on outboard gearbox

[baghira]

Guys...
I have a Johnson 4 stroke 70hp, and the shaft/gerabox was all corroded, the paint went off...
Last summer I sanind it all down bringing it perfectly polished, gave it itching primer, and sprayed it again with hardner paint.
A year after the gearbox is back as it was before.....

Is there something to do.....
They say that the metal once it gets corroded there is nothing to do???

[Granitu]

it is difficult to cure corroded metal baghira but there is one thing I would ask you.

when you sanded it down did you wash it with acetone and left it standing unsanded for at least a week?

I find this procedure extremeley effective on metal which shows minor signs of corrosion.

what type of hardener paint did you use? Is it approved for sea underwater use for use on metal (outboard spray)?

if the hardner you used is porus it is understandable that the metal corroded again

[EmicMalta]

A friend of mine had the same problem, but he changed the kind of paint and now it s ok

[baghira]

I did not use acetone, and I used vehicle hardener paint.
Should i have eanother try??

[Granitu]

vehicle hardner paint is too porus I think for outboards.

Depends very much on how much are you willing to spend, but if you want I can PM you were to buy appropiate coat for saltwater use. A tad expensive but they do the job diligently

you should have another try baghira

[yogi]

BOERO delta 2000 , at Nautica . they have very good paints for the marine industry , or international yacht paints

[baghira]

Please granitu

[Granitu]

see your inbox baghira should do

[joe]

bagghira befor you sprey dont use aceton to clean wash only white water 

[Granitu]

bagghira befor you sprey dont use aceton to clean wash only white water 

Why?

water creates more agents to corrosion plus it does not remove the paint additives! Acetone removes even the slightest of unreached additives

[joe]

on aluminium dont use anny acit you need to remouve the salt and it is very poorest  i hope you andestend whoth i am writing

[skip]

Silvio, BRP use PPG paints so you want to use something like:

Epoxy Primer PPG DP50LF with DP402LF Catalyst
Paint PPG DCC 90538 (evinrude white) DT885 reducer and DCX61 hardener

Sand with 400 grit And clean with acetone

After spraying epoxy primer and it drying, lightly sand and clean before spraying around 3 coats of colour. Not sure if one then needs to spray a clear lacquer or not. I believe This PPG paint is not automotive paint, but more likely from their Light industrial paint.

Info from http://www.etecownersgroup.com/post/High-End-Touchup-Paint-and-Primer-5467829

This is also a very good read and guide http://www.boatered.com/forum/topic.asp?TOPIC_ID=97217

[Granitu]

on aluminium dont use anny acit you need to remouve the salt and it is very poorest  i hope you andestend whoth i am writing

joe why not use it against salt?

A reply from a chemistry knowledgeable person over the internet

"Acetone isn't that dangerous with the exception of flammability. As a chemistry major we used the stuff to clean anything. But it is not a good high strength solvent for paint. Plus it evaporates quickly and is very thin, so it won't sit on the spot you are trying to clean.

As for drying out your hands, Acetone is great for taking wet glassware and drying it. The acetone hydrogen-bonds with the water and as it evaporates, takes the water away with it."

Its purpose is to remove water particles from the part to paint so that corrosion elements (water and salt) are eliminated. It shouldn't be used on plastics but it has no effects on metal Joe.

[baghira]

Another problem is that when I sprayed, I sanded and left everything in place, and corrosion started from the cracks that separate gearbox from the rest....
So I beleive that to do a proper job one needs to dismantle the engine...

[sirena]

i had the same problem as all of you i managed to survive the second consecutive year going to the third season, i removed all the paint and brought to bare body, i uses brunox anti corrosion, then applied an antimonium paint as primer x 3 coats(its a white can berger) and used the hampel paint diluted with thinner and sprayed all.

till now all ok mind you never ever spray the anode housing cos otherwise the anode remains intact and the tail stats to corrode.

as a matter of fact after the job was done i am changing the anode yearly basically it vanished after 3 months n the sea, therefore doing her job.....