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I presume you are doing this yourself. It was a rough experience for me. For starters, you need a place to do it; outdoors or properly ventilated.Blasting will require a large compressor than can deliver enough CFM. The average 20-30 gallon Home Depot brand can do it, but it will slow you down.My engine was painted. I started with paint stripper, which got most paint off with multiple application/scraping/rinsing... repeat.Sounds like your engine is not painted: you are 75% done!Under the paint there were some stains from leaks that seeped under the paint, just like the picture from paulbricey.Bead blasting is one way to remove the stains. I carefully closed up every hole and avoided blasting near engine joints. Gorilla tape is your friend.I would not use beads on an open engine, unless done by a professional with proper cleaning.Then used soda blasting to get into hidden spots and between fins.I thought I was going to paint the engine again, but after I was done the aluminum was looking so good that I left it bare.I also suspect that only the factory can paint the engine well enough to survive eventual fluid spills and scratches.I used Simple Green to clean everything, especially after the paint stripper.Then I sprayed ACF-50 for corrosion protection... not sure how long that lasts.If you have some time to waste, here is my story: https://wildguzzi.com/forum/index.php?topic=102352.msg1691648#msg1691648
years back i had a Honda CL450. i assembled the cases, cylinders, heads, etc.. the entire engine less the internals, may some bits to close off holes, and then put the hole thing in a tumbler. It came out truly unique, it kinda looked polished, but not, it had a smooth closed finish and it greatly reduced casting lines. I would do it again, if i had a project and access to a large tumbler. just make sure the tumbling stones are smaller in diameter than the distance between the cooling fins, otherwise you will be picking stones out.
When I got my V7 motor stripped, the paint stripper shop bead-blasted it, arguing that IF any of the material remained in the case, it wouldn’t damage anything. I tried soda blasting, but either my pressure wasn’t enough, or the material could hardly get through the powder coating. I assume a good industrial or engine degreaser would work fine for the prep. If going for Simple Green, I’d used the aircraft clear version, since it’s nicer to aluminum.
I/we’ve done this multiple times. Here’s my Actual btdt personal experience using my equipment of whole assembled engines (and large assemblies), which are lots easier to do well if removed from frame-Degrease it as well as you can first. Then dry completely, like with spray of acetone or lacquer thinner. Soda Blasting. Works fine but will not remove any corrosion and some more durable coatings. Least aggressive but can still cloud polished surfaces. After you do this, you need to use air hose to remove any clogged soda in crevices, then wash extremely well with lots of water and typically use something like vinegar to neutralize any remaining soda, then more washing with water to eliminate acid…. If you don’t, paint won’t stick and if it does it won’t last. You’ll also have corrosion issues of soda residue remains anywhere, like in joints and around dissimilar metal contacts. Flash rust is hard to avoid. Read below-Regular sand blasting (like pressure pot with black beauty or plain white sand) works great if you’re not stupid with high pressure and technique. It will strip and texture EVERYTHING. Polish will no longer be polished but corrosion will be gone, too. No need to neutralize but again, flash rust is a bugger. When doing this, I prefer using used black beauty (collected from tarp under & around previous s/b work- Guzzi content) because it’s a finer mesh and doesn’t texture as aggressively. Used regular sand is usually even finer, but I don’t always have much of it to use.Ultrasonic isn’t a great method. I have a big US unit with basin large enough for some assemblies including engines, so we’ve tried it with different solutions simply because we could. It can clean but doesn’t strip, is a big PIA to seal things water tight vs just tight enough to keep blasted media out, etc. Not worth the effort.Of all the various chemical cleaners, repeated applications of professional grade, accurately diluted blue air conditioner coil cleaner (buy it by the gallon jug) does clean and brighten better quality aluminum very well. It’s not fast, but if the assembled engine isn’t trashed it’s a way to keep original surface conditions intact vs texturing caused by blasting. Pretty sure it typically has some rust inhibitors in it to limit flash rust, which is a big plus. If you use it after final cleaning of soda or sand/media blasted, it can help both brighten the alloy and mitigate flash rust. Win win.If I was going to seriously clean my CX engine-trans assembly as a unit, I would remove from chassis, soda blast it, wash & neutralize it mild vinegar and finish with several course of blue a/c coil cleaner. Then every bolt head needs paint, clear coat or some rust proof treatment or replacement to avoid rusting. But I would only use blasting to clean what I couldn’t easily remove and clean otherwise because blasting it as a unit makes for a more homogeneous overall look including texturing that isn’t original. I don’t like that. Jmho.I have yet to try vapor honing, either a real $$$ store-bought unit or the pressure washer-siphon type kit that’s cheap on line. I’ve got a pressure washer but haven’t bought or fabricated connectors to try it yet. I expect it’s a much better method than regular dry soda or regular pressure blasting.
I recently refreshed a friends V7 Sport with the motor in the frame. I used NAPA aluminum Brightner diluted 2:1, (use a full face respirator with acid cartridges), before and after, you mist the cleaner onto the castings then after a couple minutes blast with a pressure washer and keep repeating until you get the finish you are after. I did this for years before I bought a vapour blast cabinet and fully disassembled the motors. After
