View Full Version : Media Blasting.

03-23-2016, 3:01 PM
have a set of evo heads and jugs that have been severely coated with some layers of some type of high temp engine paint im assuming. I purchased the soda blaster from harbor freight with the coarse grit. the blaster worked well but was not enough to get all the paint from between the fins. so I found a sweet huge home made cabinet off craigslist and picked it up this morning. I am aware or the dangers of using media residue that could potentially get left behind. Im just going to have to be very cautious and plug any holes I can and make sure to chase threads. from searching the forums i have found that walnut shells are a good choice and they make it in a 24 grit and 12 grit coarse. hoping someone can chime with a suggestion and possible some photos of products they have used to give an idea of the finish that it will produce. thanks

03-24-2016, 4:23 AM
As a first step, I would not have started with blasting ... I apologise if it is too late state that but do so for others.

Just buy a big tin of paint thinner, enough to cover them, and leave them sitting in it for a few days. It won't harm the alloy. You don't need best grade, just "cleaner" grade. Auto spray shop suppliers sell it cheaply.

If the base is the original black powder coating, it'll largely come out clean and leave near virgin casting underneath. If it's corroded, which it is likely, it won't though, and it will need further finishing. You can safely use a slightly blunted metal scrapper, or a sharpen piece of wood or bamboo to remove awkward corners and between fins, e.g. use old chop sticks, cut sharp. Much of it will peel off like rubber skin.

There are pro grade paint strippers powder coaters etc use, but they're pretty heavy chemicals to use and get rid of after (depending on local regs, you have to sign the stuff out and use a proper dump to get rid of them). I've heard of folks using domestic paint stripper, but I've never tried it seriously.

Once the bulk of the paint has been remove, then I would considering your blasting options to finish, both rough (to remove obstinate burnt on paint and corrosion), and fine (to put a surface on it).

I discovered this the first time by making the mistake of putting it out to have aqua blasted (which could not remove all the paint, especially between fins). However, pro aqua blasting with glass beads does gives the best finish, IMHO. (Never tried walnut shell and others).

If someone's going down that route, it's still a bit of an art though, and needs someone to fine tune it on the basis of experience, e.g. choosing and mixing different beads and grades. Not all beads are equal. If you're considering doing so, also speak to the blaster and ask them when they change their beads, to get it done with a new batch. It's no skin off their nose, but it makes a difference to the end result. It's one of those things that seems simple, but the more you get into it, the more you discover there is to learn. And it costs to do so.

Or learn not to be too picky.

If I was doing mine all over again, I'd

a) do the thinners trick first
b) do the rough blast myself with a 'total loss' home kit, as you are doing, then
c) send it for final finishing to an aqua blaster.

I found home/dry blasting leaves them dull and roughens or opens up the pores of the alloy leading it to become a grease magnet, although it saves money not having to pay the pro to do grunt work. Good blasting kind of peans the surface and leaves it with a nice sheen.

A friend likes to finish his with a fine wire brush wheel ... I cannot remember, but I think it was a copper brush. Be careful about using not only steel wire brushes but also, if your considering it, polishing wheels and mops that have been used on steel, not only because the former can chew thru and scar alloy but also because the latter can "contaminate" the alloy (non-technical use) rubbing steel into the surface.

A quick spin with a loose mop after blasting also brings up the surface nicely. Won't last for ever ... but looks good on the day.

Air gun then soap and hot water for cleaning (which helps them dry well after), not solvents as, in my experience, they make the beads clump. Consider running through up threads with a tap. Don't thread any bolts in until they are absolutely clean because otherwise they can entirely pull threads outs ...

How do I know? Yah, the company I paid to do work didn't and I ended stripping crankcase threads out removing the bolts. I'd also say for you, now is a good time to consider buy a 5/16" UNC thread repair kit, and doing them all. There's only a couple of different threads in the heads and inlet, exhaust studs, rocker box cover etc ... are all the same size.

Exhaust studs are good to replace, as it's a big hassle if you have to do it once it all back together, and if you're considering that, there's some voodoo to it too.

Hope that helps.

03-24-2016, 9:38 AM
could always try soaking them in brake fluid, stuff is usually pretty good at removing paint!

03-24-2016, 9:56 AM
I've never used anything but aluminum oxide or baking soda. Here is a stainless bracket I recently blasted with a pretty fine grit AlOx.(I use a cabinet that recycles endlessly, so it breaks down.)

316 stainless. There are two finishes here. One is raw blasted with AlOx. The other is from a Red Scotchbrite wheel in a die grinder.
http://i26.photobucket.com/albums/c130/cggorman/Harley/bd9fc06d-c962-448c-a792-d575398e1411_zpsnadkfjjn.jpg (http://s26.photobucket.com/user/cggorman/media/Harley/bd9fc06d-c962-448c-a792-d575398e1411_zpsnadkfjjn.jpg.html)

Soda is very gentle. I have a DIY soda gun that's pretty low velocity and it produces a soft sheen on aluminum. I use it on carb bodies and such when I don't want to get into the base material.

I also have a heavy blaster that I use screened sand in (with a respirator) for heavy stripping of frames and suspension, but I'd NEVER use it on aluminum.

03-24-2016, 11:52 AM
thanks for the tips. what i have decided on is just glass bead blasting them and taking extreme precaution in the clean up. I know glass bead blasting is very split topic. but I spoke with a reputable engine builder that said glass bead has been used for many years by many engine builders in the industry. With a moderate air pressure 70-90 pounds you will not embed the glass in the aluminum and with lots of hot soapy water you can clean the media without any issues. Yesterday I bought some 24 grit walnut for my cabnit and that didnt do a thing. I have allready used aircraft paint remover and soda blasting but still have some extremely caked on shit. so I will be getting some 80 grit glass bead today and I will post some pics later and show the results

03-24-2016, 12:10 PM
Nice. You're lucky to have so much choice in media locally. I have to drive an hour to get anything.

03-25-2016, 4:17 PM
Do you have anyone near you doing vapour / aqua blasting ? That is what you need to finish with.

04-04-2016, 12:06 PM
This is a bit of an aside ... but where do pyrolytic burn-off ovens fit into this equation?

I have no experience of them on alloy pieces but I had my frame done in one to take the paint off before media blasting.

As far as I can work out "pyrolytic" means very hot.


04-04-2016, 12:20 PM
I once baked a cast aluminum valve cover to burn off some stubborn OEM powder coat. It worked, but I got some blistering due to expansion of entrained air in the casting. I probably just baked it too hot. Just be aware.