GLASS BEADING INSIDE OF VALVE COVERS AND OIL PANS

Mattax said

FWIW the exterior of these were soda blasted before repainting. Dont think I have any photos of it raw or before.
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I would call soda blasting acceptable for the inside. When it makes contact, it turns to dust and that can be washed out easily. Unless you have a way to totally submerse it though, I'm not sure I'd use glass bead or anything heavier.