Alclad is laquer base and so plastic doesn't like it.
I painted an engine in their steel colour and for some reason it just wouldn't cure at all. Even after waiting a week I could still leave a fingerprint in the paint.
I gave up with Alclad. If it can melt an expensive kit even after priming and then refuse to dry and cure then there's something wrong.
My adventures with both Xtreme metal and Vallejo Metal Color has, after a learning curve, been very sucessful as you can see above. They may take slightly longer to cure completley, but not being hot products they won't damage the kit and for me give Alclad a run for it's money.
You can use both together and side by side and because both have overlapping colours that have different shades etc then you have very much a broad shade range as well as altering the shade by using different primer colours.
For instance, try doing exhaust pipes with a red primer and then put Vallejo burnt Iron over the top of that. I didn't do that on the engine above, but to add a variance I did the air intake pipes with duraluminium which up against the stainless steel cylinder blocks draws the eye and keeps it moving over the engine.
I do go through quite a lot of plastic spoons testing metal colours with different coloured primers underneath and the variations can be very interesting and informative and can lead to different usages on engines and aircraft. You're not limited to a black gloss undercoat!
Alclad is an expensive product and it has had a chance with me. I'll stick to something that I can spray directly onto unprimed plastic if I need to with no worries that it will not reduce it to a lump of unusable styrene.
Sorry, chaps, but there you are.