Primer small parts ? (pits & gears)?

Acrylics don't adhere as well as enamel or laquer so if the parts are going to be masked I usually prime them. Likewise if I have to assemble them and do some seam cleanup I'll frequenly shoot a thin coat of primer on them just to make sure I got the seams cleaned up properly.

i usually will prime my tires cos they rub against the base/floor/shelf, but for the pit and the gear i just mist on a tiny bit to help with coverage on later coats. in fact i have just painted on top of a lightly primed 1/72 X-wing cockpit. so yeah, its up to you, if you dont feel like priming today, dont bother too much. but if you want to make sure, go ahead its not futile.