Bike frame rusting immediately, cheap frame? I've got this mountain bike, it's probably about 12 years old now, and it was sitting in the shed for years, in dry conditions. I recently decided to strip it down and I was going to respray it as it was rusted and peeling. 

The thing is, I don't know what kind of metal the frame is made of, but it seems to be a total and absolute rust magnet. The paint had totally peeled off of a lot of it, and there was rust everywhere underneath about 60% of the frame. I used paint remover to remove the rest of the paint, and the next day all these "clean" parts had rusted as well!

I went at it again with wire brushes and sandpaper, and got most of the rust off, and came back the next day and it was rusted again! It seems to be (I'm assuming) rusted inside the frame too, there's, like little (air?) holes in several parts of the frame.

So, basically I'm wondering if it's even worth the bother to clean and respray it, will it just rust again? 

Is it just some kind of cheap junk metal\frame? Should I just prime and spray it anyway, or will it just rust again in a few months, and all the paint fall off again?

The rest of the parts, while some were rusted initially, cleaned up just fine, and they've been sitting for a few weeks now with no signs of rusting again. So it's just the frame that's the problem.

Thoughts?

Edit:

Here's some photos. 

I was using paint remover to remove the paint a few weeks ago, and about 50% the paint just fell off where it was rusted underneath, and the rest of it was really stuck on there. Everything that's not rust is the leftover grey paint. I was going to start priming it at this stage, and so I went at it with a wire brush and sandpaper last week and I had just about all the rust removed.

Then I was busy for a few days, and it was sitting in the kitchen, and I came back and it was like this. The rust on it is like a layer of dust and particles, that almost rub off on your hand if you touch it.

The second image is one of the holes in the frame. It's like the manufacturers put them there on purpose, but I don't know the reason. I can hear "stuff" in there if I shake the frame, I thought it might be sand if it was sandblasted..
The fact that the frame rusted and the paint came off over 12 years is probably the fault of the paint not the steel. Even high quality strong steel alloys rust. Also, the conditions in a shed may look dry but there could be high humidity. The frame you have may not be the best, strongest steel alloy, but if you like the frame it’s worth refurbishing. 

If you strip steel down to bare metal it will react with oxygen and water in the air. You need to protect the metal with some form of oil or primer paint.

If you want the frame to look nice you’ll need to prepare the surface carefully and apply primer coats, color coats and clear coat. You can find many resources in how to do that in the internet. 

What I would do is protect the frame with WD-40 or similar while removing paint and sanding to get a good surface, then thoroughly clean with solvent and apply the first primer coat in one session. You don’t want the environment to be too humid or cold when you are doing this.



Update: I read through your question again and saw you mentioned rust on the inside and holes in the frame. You can remove rust inside with rust remover chemicals, but if the frame has holes all the way through (rather than pits) it's likely junk.