Made a quick (and very dirty) edit to show things easier, tried to stay as close to the original as I possibly could-
1. Original
2. Reverted back to lines
3. Edited the lines. Machines are (mostly) angular, and that's a good way to get the design across, as well as being much easier to work with because of the grid. Original was very off balance, fixed that, made parts fit together a little more practically, that would be a good time to use reference.
4. Made a new palette. One of the most important parts of pixelling metal is contrast, so I got that in the values of course, and shifting the hue a bit (you can see the second grey shade is blue and the fourth is yellow), which also makes it a bit more visually appealing than a straight grey scale.
5. Details and shading. I did a really, really fast job with this so it's far from perfect, but you can see how the angular lines really helped. Went with two light sources because of how strangely it's shaped, and partly out of laziness, but anyway, don't just use your colors to shade regions, use them as accents and to bring out certain areas.
It's 2 AM so I'll leave it at this, and to be honest, take most of what I say with a grain of salt, I'm much less experienced than most of the people up here.
And like I said before, don't be afraid to start back from the lines like I did. It'll do you a lot more good than editing the structure you already have.
EDIT: ...I've really made 111 posts here? ...Really? It feels like I've made maybe 50 at the most.