Note to fellow engine builders: If you aren't using coatings, you probably should be.
I've been experimenting with them since the fall of 1999, trying to figure out how to apply the stuff, which coating is best for which part, and a host of other details specific to AIR COOLED engines. Lotsa poop out there on NASCAR V8's but little to none on air-cooled VW's.
I'm using Tech Line coatings (see their web site). Some are water-based and non-toxic, safe to use in your garage. The Good Stuff needs to be oven-cured but your kitchen oven will work for the non-toxic coatings. The solvent-based coatings need to be done in a dedicated oven (it'll poison your next batch of biscuits) but for small parts -- about 90% of the things you'll want to coat -- you can cure them in a toaster oven(!) Even a used toaster-oven, like the one I bought at the Salvation Army Thrift Store for $4.00
Big stuff -- heads, crankshaft, cam shaft, aluminum crankcase (the coatings flake off magnesium alloy) -- you need a bigger oven. Muffler, heat exchangers... you nead a BIG-big oven.
But not a very hot one. 300 to 500 degrees. (The coatings are hyper-eutectic. Lookit up if you don't know.)
Expensive... sorta. But worth it. Things tend not to wear out when coated with a dry film lubricant. Muffler NEVER rusts when coated with a thermal disbursant. (I didn't believe it either. I've learned a lot in the last five years.) Ceramic coating on the valves, chamber and tops of the pistons gives you more power yet the valves last longer.
Even crazier is thermal disbursant coatings. Every surface has a characteristic heat-transfer rate. Polished surface, shiny bright like a chrome coffee pot (or those kewl valve covers the kiddies like so much), heat-transfer is nearly zilch; the smooth polished surface reflects the heat back into the engine. Rough, black surface is almost transparent to heat (which is why stock steel valve covers cool better than those niffty chrome jobbies). Then along comes the thermal disbursant. You abrade the TOTALLY degreased surface by low-pressure blasting using #120 aluminum oxide until you've got a uniform frosted appearance, then blow on a couple of mist coats of thermal dispursant with an air brush, let it dry then cook it for an hour at 300 degrees Fahrenheit.
Two things happen. The first is that the surface, be it steel, aluminum or your old jock strap, will now pass about 7% more heat than it did before, assuming you got boiling water on one side and 80 degree weather on the other. The greater the temperature differential, the the more the improvement, up to a max of about 12%.
The second thing that happens is that the surface will no longer corrode if aluminum or rust if steel or smell icky if it was your old jock strap. Seriously. (except for the bit about your jock strap :-)
Stainless steel headers don't rust. But you gotta float a loan to buy them. Now you can have carbon steel headers that don't rust. You can even have carbon steel headers that LOOK like stainless steel. But what's really gonna freak you out is that I can shut down the engine and immediately put my bare hand on the header (!) (Yeah, I know... I didn't believe it either.) The heat is there but it stays INSIDE the pipe. And if you know your onions you know that the higher the temp, the higher the sustained velocity of the exhaust gases. You end up with better scavenging of the chamber and your volumetric efficiency goes up.
That's just the tip of the iceberg. If you got a big enough oven you can put thermal dispursant on your heads and a ceramic thermal barrier on your chambers. The latter reduces the amount of heat flowing into your heads and the former gets rid of it faster. Bottom line: You can run a higher CR without detonation. Or a leaner burn. Or more advance. Or all three, if you're seriously silly about chasing a stop-watch for a quarter-mile. (Ask Jake Raby what I'm talking about :-)
But it took me a while to figure out how to do it.
The surface of the metal has to be abraided. You're creating a ceramic-metallic bond. (They use the stuff on the turbine blades in the hot-section of jet engines.) Soft metal, like the Babbitt on your bearins, you abrade with a Scotch-bright pad. Aluminum (ie, your heads), you can do with #80 silica sand or #120 aluminum oxide. Cast iron & steel, use the aluminum oxide.
One you've got a properly prepared surface and can apply the coating with a foam brush if you don't have an air brush. (Come on; Harbor Freight sellzum for $5, for crysakes! Spring for an air brush... and something to give it air.) Takes a lot of pressure because the coating material is thick as mud. And if you've got even the teeniest-tiniest bit of oil on the surface, you're screwed. You gotta wear gloves (fingerprints are oily) and use MEK, acetone or lacquer thinner as your de-greaser -- no petroleum-based solvents allowed. But once you get the stuff on and cook it, the dull poster-paint-looking surface flattens out. Then you polish it (if you wanna). Shines like new dime and NEVER comes off. Your bearings are now slipperly then they ever was before. Slippery bearings means less friction; less friction means less heat. And more power.
Doncha hate the way your end-float opens up? So coat your shims. And the bearing. And the neck of the flywheel (if you got a big enough oven). Now the thing will run longer without opening up.
Coat your BLOWER. (Seriously!) Coat the blower, it never rusts and tends to throw off the usual crude that builds up down there in the corners where the vanes are braded to the disks. Clean blower pumps more air for the same power.
Starting to sound like found-money, eh? In a way, it is. But as with anything else, the devil is in the details -- you gotta learn how to apply it and and you gotta tool up for getting the parts perfectly clean, blasted with media and so forth. So like the man said, there ain't no such thing as a free lunch. But you really gotta love what that stuff does.
You know how rockers always gall on the bottom? SOP is to turn the rocker shafts over when you give the thing a valve job, toss them when they get galled on both sides...
Fergeit. Coat the rockers and the rocker arms and the towers and the flat washers and the warpy washers and even the hair-pins with DFL (ie, dry film lubricant), do the HVX mods (delivers 8x as much oil to the rockers) and you can forget about wear on the rocker arms & shafts. Run high rpm, the washers don't wafer out, the hair-pins stay in place. Thing simply sits there and RUNS.
Should I mention brakes? Prolly not... But you don't have to be a rocket scientist to see the benefits of thermal dispursant on your drums (exterior only, please).
Lotsa other neat tricks.
Good engine, you always anodize the body of the oil pump. Based on my experiments, DFL does a better job protecting the pump... AND the gears... than anodizing. Put it on the oil pump cover, the gears stop scouring those circles in the cover-plate (burnish, yes; scour... as in wear, no).
Throttle-shaft bore that doesn't oval out. Carb body that won't corrode. Heat risers that don't rust yet run hotter than stock, eliminating manifold icing.
And so on.
Tech Line sells all kinds of coatings. I tried about a dozen, have narrowed it down to five. Baked on dry film (DFL-1), burnished-on dry film (WSX), thermal dispursant (TLTD -- one of the toxic ones, not the kind of thing you can do at home) and CBC-2 (ceramic thermal barrier coating).
No, I ain't selling nothing. And I don't have anything to do with Tech Line, other than buying their products. But five years ago when I asked questions their owner (Mr. Leonard Warren) was straight with me, telling me up-front that while some of his coatings should work okay on air cooled engines, most of his customers were building high output V8's for the race-car circuit and he couldn't offer any advice specific to Volkswagens... although he'd like to hear how things worked out.
Which was AWFUL, for the most part. (No, I didn't tell him that.) I just did it over. I'm doing okay now but that's only because I've already screwed up in every possible way, ruining lotsa parts and wasting lotsa money trying things that didn't work until I found things that did. Five years. Not every day. Experiments are expensive in both time & money. But pretty constant, step at a time sort of stuff, trying a different tack when things didn't work out, learning as I went along.
You know that oil pump I mentioned? 803 hours of run-time at an 'engine' speed of 3450 rpm. Started the experiment on 15 October 2004 and the coupling between the pump and the electric motor finally broke on 22 April 2005 (piecea rubber hose & some safety wire). I'd rigged the motor to the lights in the shop so the thing was only running when the lights were on, then I plugged an old 'digital' clock into that circuit -- the kind that flips over the little panels and ticks off the days of the week in a window? Between October and April it accumulated
33 days, 5 hours and something. That's when I took the pump apart and inspected the coated surfaces. Yeah I know -- it ain't reality, laying there running at room temp and zero pressure in pan of oil, but I think it was a good abrasion test since it was running face down and the gears had to be touching the cover plate. (There's a burnished mark but you can't feel it nor measure it.)Now take five years and multiply that sort of experiment about a hundred times -- because engines are expensive and the last thing I wanted to do was to apply some SooperDooper Coating that turned out to be total bullshit.
It ain't bullshit. And no, DON'T ask me how much more 'power' you can get. There's some and it's effectively free since it comes in the form of improved efficiency but I'm more interested in long-term durability.
Try it; you'll like it. If you run into a problem, odds are, I already did :-) in which case a private msg might be in order. But no public posts please. Don't want to clog the bandwidth with stuff nobody's interested in.
-Bob Hoover