Ceramic Coating rotors.
 

Figured I'd share this, just finished coating my spare rotors with techline CBC1. It went pretty smooth. Rotors had already been cleaned with a wire brush, I went back over them with a harbor freight air eraser (mini sand blaster) and 120 grit aluminum oxide. Then I washed them, dried them, baked all moisture off of them at 300f for an hour. Took em out let em cool down then when they were still warm and masked and painted them with an air brush. All in all they turned out very good. Had a couple spots on one side that must have had some contamination and peeled so I cleaned em back up and repainted the spots. All in all I think they look good. Dunno if the coating will last, but it's easy enough for anyone to do.

Why did you do this? Desk trinket?

Preparing for rebuild, since I have spare useable rotors I figured why not coat them now. The goal is to lower my oil temps and take some heat off the side seal springs, but who knows if it will work. Process was pretty painless though, and result looks good. Only used about 1/3 of my bottle on the rotors so plenty is left for other purposes.

Problem with recycling old rotors is that the groove is usually worn so the seal may have a lot of play. Perhaps you may be able to use taller seals successfully.

Good to see some experimentation hope it works out for you. Please post your results when you done.

i have always been intrigued with coatings in this engine. it seems like it is the perfect candidate.
If you are trying to protect the side seal springs--then make sure you also do not have any exhaust system back pressure--or very little.
Have you looked at a company called "Micro Blue"--professional teams have been using them for years.
If you are looking in doing things like metal txs and coatings during a rebuild--pay a lot of attention to the bearings , e shaft , stationary gears, oil pump chain and oil pump.
This interesting stuff.
If the seal groves and seal sides had a great coating.....???

I dunno, wouldn't ceramic coating flake off eventually? Also aren't the newer rotors coated at the factory with a proprietary coating?

yeah, if it bubbles and scrapes off during application I'm not sure how it would ever survive a series of combustion events.

:uhh:

I'm not really worried about flaking. When I researched this stuff I found a lot of people have used it successfully and contaminants on the metal will cause bubbling that needs touch up. This only happened on one face of one rotor in a couple spots that were probably fingerprints. If it comes off during combustion it will break into powder and get blown out the exhaust. The stuff that clung to the masking tape had a chalk like consistency and shouldn't be hard for the engine to expel. A lot of people use this stuff on their piston tops and cylinder heads with good results. That doesn't mean it will work well on a rotary though.

I'm not sure what to say about the side seal groove. I don't think it's that important especially since we have wedge shaped seals, but I could be wrong. Either way the seals look tight and I'm going to reuse the rotors.

O.D.: I did look at microblue, they have good stuff. Also looked at nikasil and other coatings. If I had the cash there are a lot of options I'd like to try, but I'll leave those for another day and another rebuild.

if it flakes it will not cause any harm--from what I understand at least.
Harlan--i may be wrong but I think that grove wear is more apparent in the apex seals slot than the sides. The side seal really doesnt rock back and forth like the apex seals do. That is one reason some of use have gone to the taller rx7 turbo seals in our builds.
I have always thought that since they moved the side seals closer to the combustion chamber that this too increased the heat the seals are exposed too. No proof--just seems reasonable.
I do know of one person that is experimenting with a thinner side seal to reduce friction etc. No findings as of yet.
I read a research paper this week is which the conclusion stated that (concerning the irons) a separate ceramic sheet attached to the irons would work better than a coating. I am glad research continues. Very interesting stuff.

If I may--since we are speaking of coatings--not much has been said/discussed concerning oil shedding coatings. Now I am not an expert in these things, but I am thinking that since the rotors are being cooled with oil injection ( on the undersides) and centrifugal force fights that oil from draining, should there not be benefit from an oil shedding coating applied? Many recip engines use these to increase oil drainage/cooling. I do not know of anyone that has tried this although I am almost certain someone has.

Microblue is expensive--lol--certainly understand that. Cost versus known benefit decision no doubt. I dont have the time/money to experiment either.
But Mazda is doing a lot of research in friction reduction so maybe they will do it?

Excuse my rotary naivete, but don't these rotors rub on the inner cylinder much like a traditional piston would in the bore?

Just the seals ;) If the rotors rub things are going bad fast :)

I was under the impression that even piston engines just rely on rings seals and oil to avoid actual piston to cylinder contact.

Got it, I noticed the seals after my post. That being said, if your parts are already flaking / peeling i don't recommend you running them in that state. Any peeling indicates an application problem so chances are there will be very little to any adhesion.

The problem with a failure like this is that the ceramic based materials are VERY abrasive. Letting it drag around is similar to dragging a piece of sandpaper around. If you drag this debri across the cylinder walls or across the seals you're going to expedite wear. The material is so abrasive that I go through spray gun tips and needles fairly often because of it.

Additionally, your description of being "powder like" indicates a problem, When properly cured this material should be VERY hard......


I strongly recommend a re-do before putting things together to avoid bigger problems.....

You are correct, although traditional piston engines do encounter piston to wall contact based on certain usage and specific rod to stroke ratios.

My primary concern was whether this coating was being used as a thermal barrier as it is intended or an anti-friction coating for which it is not.

PS, the likely source of your coating failure is prep. The parts need to be COMPLETELY degreased prior to any blasting. If not, you are merely blasting contaminants into your part. Also the media can NOT have touched any contaminated parts.

For us, any exhaust parts are thermally degreased in an oven at 650F-850F for about 5 hours prior to any blasting. For aluminum parts you have to chemically clean in that they can't survive any high temp cleaning.

I'm pretty sure the one rotor face was contaminated by a couple fingerprints. I masked them without gloves on and was very careful not to touch the faces, but I think i did on one. My prep could have been better, but other than two spots it turned out great, and those have been great after cleaning and repainting them. My description of the consistency may have been lacking. The over spray on the masking tape was very hard, and very brittle, but not powdery.

O.D. : I don't think oil shedders would work well at all in the rotor. The inner surface should always be coated by oil. In fact the cold oil should go to the outside and the hot oil to the inside by centrifugal force and convection. What may help is a coating that increases the surface area. I can't remember what they are called, but they increase heat transfer into liquids. Still don't understand how the engineers could ignore oil temp and nearly ignore coolant temp with respect to timing. On a rotary it's almost as bad as ignoring intake air temp.

I thought coating the irons was the way to reduce friction on the side seals, hence reducing temps :dunno:

Hopefully it holds up. The rotor's movement is very complex, not unlike the agitator in a washing machine, which is designed specifically to knock stuff loose. I'd hate to think what might happen if ceramic bits started floating around inside the combustion chambers.

Also, is the clearance between the middle of the rotor face and the narrowest part of the rotor housing preserved? The rotor and housing are supposed to almost touch during maximum compression, and even a thin coating on the rotor could cause it to scrape a bit.

increasing the surface area would always help in heat transfer--no doubt. I do wonder if that could be done without changing the rotors balance however?
CCP we have only one seal on each rotor tip in which to seal the combustion chambers from each other, whereas recips have 3 or 4 ! Tis a challenge.
Harlan-- i have a thought on dealing with exhaust port temps which is part of this entire package--see tech thread.
Following with interest.

Even when professionally applied it hasn't proven to be useful for anything more than providing the master debating theorists more material to fwap with

Very true Team. I suspect that taking heat off the surface of the rotor will cause the side seal channels to run cooler and will allow the side seal springs to keep cooler, but there's no proof. It's entirely possible that mazda fixed the problem by increasing the omp rates/third injector and coated rotors, but there's no proof of that either.

I'm not worried about the motion of the rotor flinging the stuff off, if you had enough force to fling paint off a surface then other things would be failing first. The clearances between the rotor and the housing aren't that close even at tdc otherwise carbon buildups would cause the same problem.

Coating the irons with a dry film lubricant could lower seal temps, but that's kinda the idea with a oiled hard chrome surface and iron seals. I doubt any dry film lubricant would last long on an end iron.

Ceramic on the end irons was tried, can't remember where I read the study but I saw it just recently. The result was trapping heat in the side seals/oil coating and very early side seal failure, same with coating the housings. The seals produce heat just by rubbing and that heat needs to go somewhere. The only surface the seals don't touch is the rotor itself.

I'll be coating my exhaust sleeves as my final step, that will allow me to check how the coating has held up by simply pulling my exhaust manifold.

Side seal heat exposure occurs as they pass over the side exhaust port opening

Yes and from friction with irons. They then need to reject that heat to the rotor. The cooler the rotor the cooler the side seals, the real question is how much of an effect does that have.