MemphisMooney Posted March 2, 2014 Report Posted March 2, 2014 Hello everyone, I've got a 66 M20C on which we are replacing the alternator. Upon opening the battery box, I noticed severe corrosion on the box lid. All of the corrosion was behind a plastic cover that's riveted to the metal and sprayed or coated with some kind of black material. I took the top home covered it with baking soda and water and watched it fizz for a solid thirty minutes. Believe all the corrosion is now gone, but the black coating is shot which I believe protected the lid from getting corrosion between the plastic panel riveted to the aluminum. Anyone know what this black stuff is? Photos were AFTER baking soda and nylon brush treatment.
N201MKTurbo Posted March 2, 2014 Report Posted March 2, 2014 I strip it. Paint it with zinc chromate. Then paint it with black rustolium. I'm not sure what Mooney used originally but I'm sure there are better paints now.
N201MKTurbo Posted March 2, 2014 Report Posted March 2, 2014 Aircraft spruce sells Randolph acid proof battery box paint.
flyboy Posted March 2, 2014 Report Posted March 2, 2014 Could it be wingwalk? The stuff that they put on the area of the right wing that you walk on.
KSMooniac Posted March 2, 2014 Report Posted March 2, 2014 POR 15 would be a decent choice too. Sent from my ADR6425LVW using Tapatalk
47U Posted March 2, 2014 Report Posted March 2, 2014 And when it's time for your next battery, glass mat vs flooded is the way to go. Concorde makes a good one. The bottom tray in my battery box was corroded through... Luckily Dan at Lasar had a box bottom in stock. It was pricey at just shy of $200, but cheaper than the whole box at more than $700. I've had not a speck of corrosion in the three years since I put in the Concorde.
MemphisMooney Posted March 2, 2014 Author Report Posted March 2, 2014 Thanks everyone for the responses! I'm guessing it is the Randolph paint based on the description on Aircraft Spruce website - it looks like an asphalt coating.
MB65E Posted March 2, 2014 Report Posted March 2, 2014 The acid proof paint is thinner than asphalt. It works well, takes a while to dry. Overall great stuff. -Matt
Mooneymite Posted March 2, 2014 Report Posted March 2, 2014 Iwas told the black stuff in the battery box was fuel tank sealer. (?) Makes sense that it's breaking down about the same time we have fuel tank leaks, but I have no assurance that this is anything but someone's guess. I bet Bill Wheat knows!
carusoam Posted March 2, 2014 Report Posted March 2, 2014 The acid is gone but the corrosion damage remains.... The plastic insert keeps the battery from bumping the top of the aluminum box. Sealed battery technology works wonders... Make sure there are no altitude limitations on the sealed battery if you go that way. (there used to be). Best regards, -a-
HRM Posted March 3, 2014 Report Posted March 3, 2014 Aircraft spruce sells Randolph acid proof battery box paint. That's what the black stuff is. Put on multiple coats.
MemphisMooney Posted March 3, 2014 Author Report Posted March 3, 2014 Thanks again everyone. Any advice on stripping the old paint from the plastic? Should I just flake off what's loose and paint over the old (not my preference)? I've got some Randolph on order.
MB65E Posted March 3, 2014 Report Posted March 3, 2014 I wouldn't worry about the paint on the plastic. If it is still there it will probably be there for a lot longer. Just scuff it up with some 250 grit or so. I'd be more concerned with the corrosion under the plastic pieces. If there was a way to remove it then strip and treat the lid that would be the best bet. I've seen way worse. You could get away with scuffing the entire thing, priming then putting the acid paint on the lid. Just depends on how excited you are. -Matt
MemphisMooney Posted March 3, 2014 Author Report Posted March 3, 2014 Thanks Matt. The plastic is riveted to the lid, so it's possible to remove if I want to re-rivet. Still thinking on that. The plastic is actually bowed out from the corrosion that was behind it so I'm guessing worse case is that I spray primer and acid paint behind it. Since there was corrosion I'm inclined to do it right and remove the plastic to fully treat the metal behind it. Pay now or pay later right?
MB65E Posted March 3, 2014 Report Posted March 3, 2014 Go for it! The red scotch bright wheels work well for removing corrosion. Autozone, Wally, or napa, have the little 3m buzz wheel kits that work in any drill. Business Aircraft Consumables offer replacements for other larger jobs.
PLN_FXR Posted March 21, 2014 Report Posted March 21, 2014 Thanks Matt. The plastic is riveted to the lid, so it's possible to remove if I want to re-rivet. Still thinking on that. The plastic is actually bowed out from the corrosion that was behind it so I'm guessing worse case is that I spray primer and acid paint behind it. Since there was corrosion I'm inclined to do it right and remove the plastic to fully treat the metal behind it. Pay now or pay later right? Remove the plastic insulator, or your lid will continue to corrode under it. You'll want to paint the lid with bituminous paint (such as the "acid proof paint" mentioned in previous threads ... as if ANY paint is truly acid proof) prior to reinstalling the plastic insulator. Down the road, verify this area is checked during each Annual Inspection and properly maintained - feel free to verify it is kept clean and dry yourself, especially after charging the battery in the box or after any issue with overcharging or undercharging in flight. Another previous posting mentioned POR-15 ... this is great stuff and almost indestructible
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