I plan on pulling my engines, etc, for a bilge redo. I plan to paint my blocks, trannies, etc. Just curious, when you paint a engine block that is already painted, how do you go about prepping?? Im guessing a good degreaser, then maybe a final wash with dish detergent?? Any thoughts on this?

I used prepsol for final cleaning. Then rattle canned the block.

for most metal prep - especially aluminum but also cast, etc... I like por15's "marine clean" product after a thorough degreasing. It's an etching cleaner and if you paint shortly thereafter will make a difference in how well the new paint adheres. I paint pretty much all engine parts with 2 art single stage urethane these days and use dupont nason line more than anything else. I shot a couple coats of their etch primer on individual parts and pieces as they're ready (you can get teh primer in a rattle can) and then after I have a lot of or all the pats in primer, shot it all in single stage urethane at once. It's really hard to beat the gloss and durability of these products - MUCH better than a rattle can job. Note that I'm a backyard hack - not a pro and do all this kind of thing using a $10 harbor freight touch up gunt and a small cheap air compressor.... do it outside on a calm day and wear a respirator mask with a fresh set of particulate / organic vapor cartridges. YOu'll be pleased with how it comes out - MUCH better looking than a rattle can job... imho

You can probably have the stuff "blasted" pretty cheap, that would take off ALL the scale, rust, old paint, etc [can do it yourself with a wire wheel, just takes longer and its DIRTY!] I dont know if you boat in fresh or salt water, but, instead of painting, powdercoating is an option?

If you are looking for something, cheap and durable and it doesn't necessarily have to be "pretty" the best stuff I have found is "bedliner" the stuff you can buy to do pick up boxes. Last year we restored a buddy of mine's Chevelle and did the frame in it, it looks good and is pretty much INDESTRUCTABLE, cleans up nice with a powerwasher too, I actually did my car trailer frame with it too, works well

Michael

I generally use a wire brush and degreaser to give it a good cleaning. If I'm really being anal about the final outcome I'll use a 90* die grinder and sand/scotch bright it. After that I use Dupont paint prep (I was told that brake cleaner does the same thing and its cheaper). I have a local auto paint store that will put any paint in an aerosol can for me. I think that the pre-mixed auto paint is 10X's better than the crap they put in the can on the shelf. I probably pay a little more doing it that way but to me the couple of dollars that I would save dragging out the air compressor, etc. to paint one motor isn't worth it.

as an aside / addition. the best quality 3m automotive rubberized undercoating in the rattle can is awesome to do the oil pan / botom of the engine with and will resist water and rust far better than any paint...