Why is my fresh paint wrinkling on a 1955 locomotive I'm restoring?

The wrinkling you are seeing is a classic adhesion failure. Sanding down loose spots and painting over the rest is a risky move with old enamel, even if it looks solid. New paint requires a stable, clean substrate to bond to. Old automotive or industrial enamel, even when it’s not flaking, has a surface chemistry that actively resists modern primers and paints. If you don't strip back to bare metal or apply a full-coat chemical etchant or etching primer over the entire body, the paint will eventually pull away from those compromised sections, likely following the same pattern you’re seeing now. I’d advise taking the entire thing back to bare metal if you can manage it. If you absolutely cannot strip it, you must use a specialty bonding primer designed for severe adhesion failure and previous non-porous coatings. That primer will give the new paint something to grab onto, wich is far better than trusting a patched surface.

As for the tape on the windows and headlights, don't just yank it. The adhesive is designed to be stubborn. The trick is heat. Use a standard hairdryer or a low-setting heat gun to gently warm the tape and the edges surrounding it. This softens the glue without affecting the glass or the fresh paint. Once the adhesive is pliable, you can lift it slowly or use a piece of mineral spirits or a dedicated vinyl remover on a cloth to soften the remaining residue. Avoid using sharp blades right up against the glass or the painted panels, as that'll damage the edges. Just warming and softening the material is usally enought to release the old edges cleanly.

That wrinkly stuff happened on my old truck hood once when I painted latex over something I shouldn't have. Looked like alligator skin, no fixing it, had to scrape the whole thing off with a scraper and start over. Learned my lesson the hard way about painting over unknown old finishes.

wierd question but how do you even strip something that big? Like sanding a car hood is one thing but a whole locomotive body sounds enormous. Is there some kind of machine for that or is it just hours of grinding away by hand? Also curious how long the booth rental lasts, sounds like you're on a clock.

Worth checking wheather the old coat is lacquer before you commit to anything, since a lacquer base will wrinkle like that even if the enamel on top of it seemed dead solid, because the solvents in the new coats re-soften the layers underneath no matter how many years they've been sitting there. Rub a rag with a little lacquer thinner on a hidden spot and see if it transfers color. Also, since you're in a rented booth, are you paying by the day or the job? That changes the strip-versus-seal math alot if you're on the clock.

For whoever asked how you strip somthing that size, you don't sand it, you blast it. Back in the shop days we'd send anything big thru the sandblast rig, and these days there are mobile blasting outfits that'll come to you with soda or dustless setups. Cheaper than a month of hand sanding and you get every last bit off the lower panels where the wrinkling started. One thing though, on a 55 the old paint very likely has lead in it. Grab a test swab before you go at it, and if it tests hot keep it wet and wear a real respirator, not a paper mask.

Painter here, been doing heavy equipment for 19 years. One thing I'd add is that the wrinkling showing up where the coats went on heavy is a big clue. Thinned-out paint over old enamel usually just dulls, but a thick wet coat will swell the old finish no matter what's under it. On my jobs I keep rolled coats under 2 mils dry each pass. Two weeks on tape is nothing, it'll come off fine with the heat trick.