Engine: To paint or not to paint aluminum and bronze parts
I've just removed what seems like several pounds of paint from some engine parts which turned out to be cast aluminum (crank pulley, exhaust manifold, etc) or bronze. I'm tempted to leave them free of paint as they look very nice but it appears that the "normal" thing to do is to paint the entire engine the with the same paint. Would it be a mistake to leave these parts bare? I.e. would I be risking corrosion or other problems?
I don't think there's a certain answer. Aluminum alloys especially vary in their reaction to salt air. Many will develop a white oxide coat (which stays soft and continues to wear) in just a few weeks of salt air. Others are unaffected. Who knows which ones you have?
But then again some makers, particularly "Westerbleak", paint everything in sight including all the rubber parts and fittings which the rubber companies say should never be painted. Because it looks pretty and is easier than masking, I suppose.
Since you've got them all clean...shine 'em up, apply some wax or polish or other product, and see how it goes after a week, a month, six months. If they stay looking acceptable, by all means leave them that way. If they start to get ugly or show white powdery residue, it will be time to prime them (aluminum needs special primers) and paint them.
But of course any "iron" parts will rust, if there's no oil film, no paint, no nothing to protect them. Or at least, form a light coating of rust. Even on a car, the bolts under the engine compartment are protected well enough by an oil film, but they'll bloom with rust within a few days if they've been steam cleaned and the film knocked off.
Things like the exhaust manifold require special high-temperature paint, and usually you have to run the engine so it heats up and bakes on after being applied. Makes a bit of a stink while doing that, too.
Thank you ... very helpful!!
Great post from HS, as usual...
I think the biggest thing with engines is to keep them clean - frequent wipe-downs with an oily rag will help, getting onto any leaks in quick time will prevent a lot of corrosive events there - esp motor mounts which, when rusted, will be difficult or impossible to adjust when you most need to.
Now that you're at the 'clean' stage, it will be easier to keep it there than it was to get it back to that state.
btw our club will be at Snug on the 26th.. what boat are you on? Maybe we'll say Hey....
Thanks for the reply. Our boat is Ariel, a 1970 30' C&C Redwing in slip C19 (were moving to D40 ~May 1st to avoid the dog crap!). What club/boat are you?
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