Want to (can I) use 2K Urethane over 1K paint

I looked at 19 pages on this forum and didn't see a direct answer to this question. Hopefully, someone else could use this info, too.

Before I owned it, my 1955 Ford 860 was painted (some 15 years ago) with the red-orange paint. Most likely enamel, and they missed many spots. So now I have the front-end axles off for a repair, and I want to get fresh paint on the axle parts as well as the whole rest of the tractor.

So a typical scenario...I go down the budget road and sprayed just the front end parts with Rustoleum Metal-Etch primer, then VanSickle's red-orange to match the existing paint, then VanSickle's clear. Looks great now, but then I read about the durability and the longevity of a 1K product. So after it dried a few days, I was able to dig a fingernail into the paint; NOT going to work for me. Plus I really don't like the red-orange and want a true red. Yes, it's becoming more of a restoration project at this point. So now I changed my mind and want to invest in a 2K product, probably Polyurethane. But, where do I go from here?

Is there a way I can "seal" the rattle-can paint I just put on the front-end axles and proceed with a 2K paint, or do I need to sandblast it back off to bare metal? Please be specific if there are certain products and brands of products that would work better for this application.

Then there's the question about painting over the old paint on the rest of the tractor (probably enamel, maybe with hardner); It's been in a garage for 12 years, and it still faded. I may have seen some info about that on another post, but it would be nice to have some answers here, too.

Thanks for help and the information!!!

The only place you need to use primer is where you get down to bare metal. It's kind of a crap shoot whether you can put a urethane clear over the top of rattle can paint. If you read the instructions on the clear it will probably say to shoot one coat and let it dry a couple minutes and shoot a second coat. This is probably too much for rattle can paint and will eat into it and lift it. Be sure to try it on some small pieces first and see if you can get away with it. You might need to put one coat on and let it dry several days and then scuff sand it before you put a second coat on. Probably your biggest issue is you might need a sixty degree minimum to use the clear. Be sure to carefully read the instructions on the data sheet on the clear and ask questions to the supplier if you are unsure.

The clear you are showing is lacquer, not urethane, no way I would put that over enamel.

My apologies, David, for not making myself clear. Right or wrong, the clear lacquer has already been sprayed on the red-orange enamel. I'm wanting a 2K urethane, and although I didn't mention it in the original post, I'm seeing where a 1K Urethane is working well for some folks. So my original post is asking about what options I have, or what I need to do to the parts I've already painted, as well as painting on top of the old enamel on the rest of the tractor. Thanks for looking.

A urethane won't adhere very well to lacquer. If you have gotten away with putting lacquer over enamel I would continue with that. Just don't rush it. Lacquer works by melting into previous coats so you could still lift the enamel if the solvents soak into it. Let each coat of lacquer dry for days.