lower unit corrosion

[opti al]

The way my boat sits the scags and part of the lower units are always in the salt water. recently when I pulled the boat out I noticed alot of corrosion and pitting, some areas quite deep.Is there a way to repair this. Also what would have caused this. the motors are 2000 Merc 150 optimax.

 

[rodbolt]

Re: lower unit corrosion

hello<br /> carefully sand ,prime with zinc chromate and repaint with phantom black. make sure no regular copper based bottom paint is on the units. if there is use a chemical stripper and get it off. copper and aluminium form a battery in the presence of an electrolyte. the gear case loses electrons and thus the pitting. after repainting you can paint the aluminium parts with a special spray paint to reduce fouling. if the units cannot be trimmed fully out of the water then leave them all the way down so the anodes can work. in a heavy growth or barnacle bill area you may want to put muffs over the water intakes to prevent clogging. my 120 sits totally in the water all year. and has for the past 4 years.,<br /> good luck and keep posting

 

[DJ]

Re: lower unit corrosion

opti al, <br /><br />I second rodbolt's suggestion exactly.<br /><br />If your anodes are not touching the water, they cannot protect the engine(s).

 

[opti al]

Re: lower unit corrosion

tried the zinc primer and phantom black paint already. It wore off in a few trips. any suggestions how to fix the pitting. It's a little worse than just cosmetic because the drain plug area is involved.luckily no water has penetrated yet. I priced new lower units and would rather not go that route.

 

[rodbolt]

Re: lower unit corrosion

hello<br /> if properly prepped the paint will stay for a while. even the factory paint will wear off.but the surface prep has to be very precise<br /> all the way to the acid etch. you cannot use any abrasive that contains metal. this will eliminate most wet or dry carbide grit papers. never ever wire brush aluminium and then try to paint it. the steel wire will impregnate the AL and will peel the paint back off.sounds like someone either bottom painted the unit or there is some stray shore power . you can test for stray currents with the quicksilver tester<br /> good luck and keep posting. you may also try taking the units to a good body shop and get a baked on finnish

 

[alcan]

Re: lower unit corrosion

Hi Opti<br />As the others have suggested, you need to leave your motor all the way down. Then work out a sacrafacial anode bonding system. The anodes that come with your motor may not be enough for your harbor (moorage). You may need to add more. It has been my expirence that when an area starts getting attacked, such as your L/U, it will continue even after more zincs are added. Your pitting can be repaired. You can have it welded up, or use a filler. This filler will be a marine bondo putty type stuff. Again as previosly suggested, prep work is the key here. If a good job is done, it should cure the problem and last a long time.

 

[DJ]

Re: lower unit corrosion

opti al,<br /><br />Also try washing the units with a 50/50 soulution of vinagar and water before applying the zinc chromate. That will nuetralize and clean everything.<br /><br />Motors down.

 

[vidar]

Re: lower unit corrosion

Hi! the only thing that will cemicly bnd w aluminium is etchprimer for alu....but you can also use epoxyprimer if properly prepped and used over whole the l/u..min 4 layers...used that oon my suzy..just grinded it completly clean first...had some corrosion and pitting after a seson in saltwater.. this season completly clean...