I would
not use garnet grit for blasting
anything made of aluminium. It's too angular and sharp for the purpose, and tends to embed into the surface. Fine for harder metals, e.g. steel and cast iron, though.
Soda media is preferred for aluminium, or polymer [plastic] as a second choice. Glass beads are a distant third, for the reasons given above. Edit: got my threads mixed up; to quote what I said elsewhere: "I'd consider soda blasting for the crankcase, too. The problem with glass beads is that they get stuck in all sorts of nooks and crannies, especially tapped holes. And they're buggers to get out of there! If you aren't extremely thorough in cleaning them out, it only takes a couple of them to get into a bearing or such, to wreck it."
Although the local aero engine rebuilder down this way does use glass beads, there's a lot of post-blast time in meticulously cleaning out all of the blind cavities and tapped holes, in even a 4-cylinder Lycoming or Continental crankcase. I've watched it being done.
They also had a set of Lycoming IO-720 cases in the racks there [720 cubic inch, flat 8 layout], and I shuddered to think about doing this cleanout job on those.
Hey Gadge!
Can you tell me or does someone on the forum know if it is OK to use plain epoxy etch primer on an aluminium engine and then use enamel over the top. I already have a can of Hichem Super Etch Primer (grey) and went out and bought Dupli-Color Engine Enamel (Chevrolet Orange DE1620).
Dunno about the temperature limit of that primer; I doubt it's up to the job on an air-cooled engine crankcase though. VHT do make a
High-Temp primer, and I'd use that, or an equivalent.
