Problem

[Rob-M]

I'm doing a pair of V8 rocker/cam covers and came across this problem.



It actually looks to me like water marks for some reason (it's the best pic I could get of the fault). The area is very shiny with 1st stage polishing but looks like a cheaply made mirror with the faults shining through from behind. I've sanded twice and every time I hit it with a mop it comes out like this. Basically I'm asking if I need to keep sanding until this disappears or is it an inherrant fault in the material. BTW they are Rover covers 3.5L (Buick designed engine I think, but probably UK made from a long long time ago)

Cheers
Rob

[CarWiz]

I can't see anything in the picture but many cast aluminum parts are pressure formed from powder or pellets. This could be one example. If it is, I think you're SOL as far as getting it polished. You can try sanding it down but you may uncover voids or inclusions. Borrow a camera and get better pictures.