Coatings

COATINGS - 8 MAY '05

MEDIA BLASTING

Yes, Harbor Freight's 'Gravity Feed Spot Blaster Gun,' 45998-1HHH @ $19.99 will work. But it's slower than hell, requiring constant refilling for an object of any size.

While #120 silica sand is the least expensive media commonly available it has a number of disadvantages, the most obvious being it is a one-time-use media. It comes in #50 pound bags (about $2/bag) and most real lumber yards stock it. But you'll probably need two to three bags for one engine's worth of parts. I'll assume you know about silicosis -- the dust from this stuff is deadly. A good respirator is an absolute necessity.

If you're not familiar with media blasting you'll find it's one of the worst jobs in the world.

When using silica it's best to work outside. If you use a blasting cabinet you'll simply keep recycling the stuff and after the first pass the texture of the abraded surface will not have enough tooth to give you good adhesion CermaLube or CBC-1. So work outside; someplace where the sand can be cleaned up and spread in your garden or whatever.

At the very least you want to be wearing a painter's hood (Harbor Freight again. Cheep; about three bucks.) Ideally, you should be wearing a full coverall. The Tyvex jobbies are okay and American Science & Surplus had them for two bucks a pop. One size fits all, which means lots of duct tape.

If you've got a breathable air supply (an HVLP compressor works good) and the mask, then a regular sand-blaster's hood is probably the best way to go. Cheap bastards (like me) make do with the painter's hood and a full face shield. (HF, McMaster-Carr, et al) The bubble shields are handiest as they provide more room for a double-canister respirator.

If you've got a blasting cabinet then the best stuff to use is #120 aluminum oxide. It is reusable and you'll get a 'sharper' surface faster than with silica.

I've found the best way to do the hair-pins and the flat & warpy washers (ie, valve train components) is to use a vibratory polisher about half filled with #120 silica sand. (I re-load for seven calibers, have a big tub-type vibrator and a couple of smaller drum-type tumblers.) If you're only doing one engine it would be silly to buy a polisher; you can do the washers one at a time, holding them in your gloved hand. But if you've already got it, it makes sense to use it. In fact, it does such a nice job on the small stuff that it's worth your time to try and borrow one.

The valve train components get DFL-1 which is a little thinner than CBC and forms a good bond with the finish produced by the vibratory tumbler. (It is presently loaded with my entire stock of thrust shims (quite a few). After being coated & baked I'll re-mike them and sort them back into groups.)

To spray the small stuff I place them on a piece of 1/4" mesh hardware cloth so the air-brush won't blow them around. DFL air-dries fairly fast but I put the panel of hardware cloth -- with the sprayed parts on it -- into a warm oven for 30 minutes before I flip them over and do the other side. Then another pass through the over.

Don't touch them with your bare hands.

After being sprayed I thread the small stuff onto piecces of 1/8" welding rod that I've already abraded and coated with TLTD. That was to guarantee they were perfectly grease-free and to set them apart from other wires, rods and what-not.

Two pieces of 2x2 angle iron were treated in a similar fashion. One edge is notched with a cut-off wheel every inch.

The angle iron goes onto the middle shelf of my oven and gets pre-heated for about fifteen minutes. The welding rods are suspended between the two pieces of angle iron; the notches keep the rods from sliding about. The small parts spaced so they can't touch each other then the oven is brought up to 300 degrees F and the coating is baked for one hour. Unless I need the oven for another batch, I let them cool in place.

A toaster oven is large enough for this type of work but be careful to shield the parts from the heating elements. It's okay to use your regular cooking oven for CBC-1 (piston tops, combustion chambers & valve heads) and DFL (piston skirts, cam, lifters, valve stems, cam gear, bearing shells, oil slinger, prop flange sealing surface, distributor driver-gear, shims & small hardware, rocker shafts, rocker arms, oil control valves, oil pump body & gears and oil pump cover [interior]). But the thermal dispersant (TLTD) is solvent-based and toxic; you don't want to cook it in the house. That means you'll need a different oven to do your heads (all exterior and the interior of the valve gallery) and valve covers (inside & out) push-rod tubes (exterior only), pistons (interior), rods, sump plate and the exterior of the oil pump cover.

Harbor Freight has a medium-sized Powder-Coating oven that is large enough to handle a head stood on end (item #91979-0HHH [that's a zero]) but at $130 it seems a bit over-priced since it's only 500W and does not have a fan.

The more massive the part (heads, camshaft, crankshaft, rods) the more difficult it is to maintain an even top-to-bottom temperature. Since the heads would have to be stood on end -- on fixtures you would need to fabricate (and then bake-out and, ideally, coat to prevent contamination during baking), it might be best to look for a used household oven that you can rig with a fan. (Keep the fan-motor on the outside of the box, penetrate the wall with the shaft, put the METAL fan-blade inside, ideally in the top of the box blowing down... but not blowing too hard. [If you can't regulate the speed, try flattening out the blades, making them smaller or using a multiple number of smaller fans.] Temp-L-Laq, a brush-on temperature-sensitive lacquer is available from welding supply houses. If you have to build your own oven you'll need to confirm both its temperature and temperature distribution.

Other than the valve covers, which you can simply sit on the oven's rack, all of the components mentioned above will need fixtures to hold the parts while they bake. Since the fixtures must fit your oven, the largest oven you can afford is probably the most practical, since you can put a small fixture into a big oven but the reverse may not be true.

Small ovens have a definite advantage in that they cost less to operate and take less time to reach the proper temp, making them more convenient when doing test-batches.

If you can't afford a seperate oven then you'd best not use any of the toxic coatings. Your main goal is to do the combustion chambers, valves and pistons.

I've largely limited my experiments to coatings YOU can safely apply AND which are available in small quantities. As you've seen on the Tech Line website (

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) they offer abroad range of coatings that might be used on flying Volkswagens.Unfortunately, a lot of them are sold only in larger quantities or aretoxic. Another coater gifted me with the residue of a quart ofCermaLube which I 'rejuvinated' and used on some experiments,including a pair of telescoping landing gear legs. The it isn'tchrome plate but it does provide all-weather durability pluslubrication.

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Until a coated VW has flown a few hundred hours it's impossible to evaluate the worth of the coatings, which makes it difficult to justify the expense of a big oven, a blasting cabinet and so forth. But over the last five years, during which I've made every imaginable error while learning how to use this stuff, one of the lessons learned was that half the battle is in having the proper tools. The holding fixtures are important but as the experiments progressed the necessity of a good oven eventually overshadowed all other considerations. And by 'good' I mean something you didn't have to sit beside and constantly monitor with a fire extinguisher in hand. An electric oven is the most convenient plus it eliminates the combustion products found in the typical gas oven, some of which (mostly water, I believe) interfers with some coatings.

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Bearings are not a big issue in flying Volkswagens because they will usually out-last two or three sets of exhaust valves. But applying DFL-1, the dry film lubricant, to bearing shells is dead simple because you do not need blast the soft Babbitt coating. Simply burnish the load-bearing surface of the shells with a degreased Scotch-bright pad, apply DFL, position in the oven (you don't even need a holding fixture) and bake. Ensure your temperature does not go above 325 or you'll start sweating tin out of the Babbitt metal.

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I found that the best fixture for holding small parts while they were being coated was my gloved left hand. Most gloves proved uncomfortable. Inexpensive vinyl gloves that come in a roll proved to be handier than any of the others. When gloves are difficult to put on and uncomfortable to wear, there is a tendency to try to do without them, leading to contaminated parts and coatings that did not bond.

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CBC-1 proved to have a shelf-life of about a year. If you are planning to use coatings, assemble the necessary equipment first then practice on junked parts and do not buy the coatings until you're ready to use them. Common water-based poster paints are similar in consistency to CBC and slightly thinned, to DFL, allowing you to practice their application inexpensively.

You need to learn how to hold and rotate the parts; how to pick them up and put them down without distrubing the coatings. Such practice will also confirm the design of your baking fixtures.

Practice is also needed to learn how best to hold & rotate parts being blasted. Five years ago it took me nearly half an hour to produce a uniformly blasted rocker shaft. Today, I can do one in about three mintues.

When doing such practice sessions it might be a good idea not to allow any visitors in the shop. Since some components require multiple coatings (valves, pistons, etc.) I used different colors -- yellow, red, green and blue, all quite bright. There's really nothing you can say to offset the impression given by a tray of pistons carefully painted in carnival colors, especially if the person is (or was) a potential customer :-)

-R.S.Hoover

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veeduber
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