I would strongly discourage you to try to try to media blast your engine in the frame, regardless of method, as you probably will blast on places you didn’t intend to.
But lets look at the basics.
There are a number of different blasting methods.
Dry blasting
Is when you blast with dry media as aluminum silicate, sand or glass that is accelerated and driven by compressed air.
This is a very effective way to remove oxidation, paint and so on, on stuff that is not very sensitive. Think ships, bridges, trailers, car frames, steel rims (bike frames if you use small grained sand and low pressure.) as the blasting media is very aggressive (spiky) and will remove material from whatever you are blasting.
Residual media: Dry blasting will leave residual blasting media and there for require very thorough cleaning after blasting or you will find blasting media in places where you don’t want it.
Finish: Dry blasting leaves a rough finish suitable for painting.
Vapor blasting,
Aqua honing or wet blasting is when the blasting media is mixed up with water to form a slurry, that is then accelerated and driven by compressed air. The media is usually small spherical glass beads, and this is a excellent method when you want to blast sensitive stuff like engine parts to remove oxidation, carbon deposits, burnt in oil or paint. This as the water dampens the glass beads when they hit the material you are blasting. There for you can blast high tolerance parts like pistons, internal engine parts without removing material from what ever you are blasting. Furthermore you get nice polished surface compared to dry blasting that leaves a rugged surface. But Vapor blasting is not aggressive enough to remove 2k paint or powder coating, that has to be chemically striped first. Then it’s not always the best way to go if you want to blast steel parts as the water will make your parts flash rust if not the adequate precautions are taken.
Residual media: Vapor honing will not leave blasting media imbedded in the material you are blasting as can happen when dry blasting, but still requires thorough cleaning after blasting to make sure that all residual media is removed as You don’t want to find those beads in your engine.
Finish: Nice polished looking finish, but it is dependent on the material you are blasting.
Soda blasting
Soda blasting is even more gentle than Vapor blasting, in soda blasting the blasting media is bicarbonate crystals that can be blasted dry or wet, if wet it requires the slurry to be saturated with bicarbonate to a level where the water will no longer dissolve the bicarbonate.
This can be used for really sensitive stuff, but being so gentle it’s hard to remove burnt in deposits.
Residual media: You can easily rinse of the remaining media with water.
Finish: Being so gentle it’s hard to get an even finish ant the surface you are left with is often patchy.
Dry ice.
Dry ice is even gentler than soda and is probably the only method I would use on a engine that is still in the frame. Here the dry ice pellets are blasted dry and when they hit the material you are blasting they sublimate and turns in to gas instantly by a very rapid expansion that helps method to remove oxide and grit. This method is often used on electrical components like electrical motors to remove grease and dirt and on wood to remove mold from mold infected roofs and basements.
Residual media: it leaves no residual media as it turns to gas.
Finish: all dependent on what you blast.
Me and my buddy runs a professional Vapor blasting business and discourage customers that wants assembled engines blasted as those glass beads finds there ways regardless of how careful you mask. We have done a few assembled engines but we always tell the customer of the risk.
So all in all, if you want to freshen up your engine in the frame there are no free lunch.
Degrease thoroughly, then arm yourself with tooth-and bottle brushes, rags, aluminum polishing compound, elbow grease and beer.
/anders