This is part of a discussion on the INOALIST from 2006 on another type of parts coating.
It also states as, Jim has said, how it wears away at tight areas, but still clings in the porosity in the worn area.
I was amazed at how Rick Simms could make parts work. I saved some of his post, this being one.
His passing was a loss to our world.
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Rick Simms <nortonwizard@yahoo.com> wrote: Sherwood,
This may shed some light on some of your questions. The manufacturer's official story is that dry-film Moly coated things, like gears, get sheered down to the appropriate interface in seconds, leaving the remainder wiithin the pores of the metal, to make for a slick surface. I once asked, "Well, just who does use this stuff?" Not knowing that I lived down the street from the place, the coatings guy said, "Well, one of our bigger cutomers is Tenneco," to which I asked, "You mean the Newport News Ship Building & Dry Dock Company...the world's largest commercial shipyard?" He said, "Yeah, you've heard of 'em?" Duh!
As to pistons, I'd wonder the same as you, if the gear coating might make up for a little slack. I don't know for sure, as I don't know how much effect the remaining amount will have, after wearing in. I had a set of Norton pistons done with the early, softer, Piston-Kote, that was discontinued. After about 10,000 miles, nearly 50% of the soft coating was still in place, much of it intact. It tapered down as it appraoached the bottoms of the skirts. Just as they had predicted, it looked just like their tech-sheet illustrations. The aluminum still showed black speckles in the porosiity, and way more than I would have expected.
I've had to take the cylinders off of the Trident twice, since I did them myself with the harder Gear-Kote. Though there was no wear to cylinders or pistons, in the nearly new engine, the fit was on the sloppy end of acceptable parameters. So I used plenty of the stuff, and baked it in the higher temperture range, for maximum hardness. Again, I was surprised to see how much was still there, looking almost untouched in places. With about the same amount of miles acrued, as the softer coating in the other bike, it was obvious that the harder version was much more durable. Less than 1/2", at the bottom edges of the skirts, showed much aluminum though it, and that was only concentrated in the center, where all the rocking pressure is placed. As with the softer version, the porosity was packed with the coating, but much more visible, and only a much smaller fraction of the aluminum was actually showing. So to answer your question of making up a little slack...I think the gear
coating can buy some time, if not seriously make up a difference. But my observations are somewhat subjective, and I don't know enough engineering to know what or how to test for real results...other than observing that it's stuill there after going through hell. I'm told you'd have a hard time putting too much on pistons, as any excess just burnishes right down to what ever nomal fit it seeks. It's definitely durable. You could argue that the oil cooler, or the synthetic oil, prevented the pistons' destruction, when it overheated and started to seize several times. But the heat and friction were enough to slow the bike down, like the brakes were on, even at full throttle. That was unmistakable, and it had been more than enough to totally destroy my friend's BSA pistons, when the same thing happened to him.
I've only seen it flake off in a few spots, once or twice, and that was only on pot- metal carbs, which always have some natural corrosion. They also hadn't been properly perpared. But properly prepped metal will just not lelt this stuff go. You literally have to abrade into the metal to scrape and sand it off. Unlike the crude bonding of paint, this is chemically bonded, so it can't be separated.
I'd forgot all about one other time I used it for something out of the ordinary. I acquired a disc front end, and the all aluminum master cylinder was a mass of corrosion. The inside was severely pitted, and I didn't know about sleeving, even if it had been available. Remembering how gear coating had restored many carbs & slides, I started air brushing layers into the master cylinder. Being a liquid, it puddles to it's own height, so the pitting was filled up pretty quickly. Of course the piston and seals would have been too tight, so I honed it out with a flap hone that I made from a 1/4" dowel. I put a slot in the dowel with a small dove-tail saw, and used a double flap of something like 180 grit wet paper. I honed it out, like you used to do to drum-brake cylinders. When the aluminum was just barely starting to show through, I dusted in one last thin coat and baked it. Once cured and hardened, I lapped & polished it one last time with wet 600 paper, to get it
absolutely true. There were no more pits showing and it looked like new, except black and polished. It's seemed to work perfectly, for years, and I couldn't see any reason the soft rubber seal on the piston would cause the coating to wear.
As you said, polishing has been shown to be effective for some things. The coating manufacturers tout this stuff for insulating and dissipating heat in those same spots. I've tried it on carb intakes and piston crowns, so far, and it polishes up like something halfway bettween paint and aluminum. though it's a lot harder than paint. I did my aluminum brake & clutch levers, the master cylinder and cap with the gear coating, as it is more durable than the protective & decorative coatings you can get. Polished up with part in dark gold, the master cyliner looks trick, and never needs polishing, again. It's had a few comments made, but I definitely don't think it looks like a zoot-suit. Unlike doing carb & slide restoration with this stuff, which takes days, restoring the bore of the master cylinder went like lighting. I haven't tried it, yet, but I don't see why, if applied and polished, it wouldn't be a benefit to already polished exhaust ports. It seems to be working in
that context on my piston crowns.
sherwood shute <nealmeal2000@yahoo.com> wrote:
my biggest fear with coatings are they might come off-one of the nicest things i can think of with coatings:they take up clearance so i might not have to replace those pistons after all-its real nice when you can't even find the parts you need anymore.I also see value in polishing some parts like combustion chambers because it helps resist heat and if they had a ceramic coating it might be more heat resistant along with the tops of the pistons.I have heard of people painting the insides of engine cases to help oil drain down but think once again polishing might have done the same thing and might even transfer heat better-a heat resistant coating on the exhaust port might be a good thing also,so if you add it all up,could make quite a difference-sherwood
