Which sort of primer?

[mat777]

Hi everyone, I'm thinkinf og repaiting a metal bike frame and dont want it powerdercoated for a) cost and b) having to remove all the cranks etc. I will spraypaint it bit by bit but want to know which primer to use. I fancied using etch primer to get a really good key, but have been told that unless I strip back to bare metal (I wont be) then it can react with existing paint? I would prefer to use etch because there are a lot of weld beads and fancy shapes that will be impossible to key-sand properly so if I have a self-keying primer then its a lot less work for me!

[Big Al.]

IIRC Etch primer is only used on raw ally. I would use just a good quality cellulose grey primer.