Resurfacing rotor housings
 

6 months back before I even knew about this forum I started a project to try to salvage worn rotor housings. Those freaking corner seals had made my life miserable a few too many times. That feeling you get right when you are about to split a motor only to find problems. Then just have let the "mourning" process run it's course.

I knew that going into this that the first hurdle would be to be able to have a controlled milling process that would not compromise the shape of the seal surface of the housing. I came up with an idea that required many trips to the local machine shop, bearing shop, etc. and built a machine to do it.
Since then I heard that there were some people talking about some people that already do this and ceramic coat the housings. I have yet to hear who they are or how much.
Anyway after kicking a couple of K into this project and tons of headache working bugs out already it is not like I am ready to throw in the towel on this adventure.

I have talked with people who do plating that tell me that they are concerned if metals are used that do not have the same expansion rate as the base metal that I will have trouble. There is also a problem with the thickness of the plating because most processes would not go down even with a few passes.
I just heard about Cerafuse that uses a process that fuses the ceramic to the base metal but I have to find out what they charge.
I have also thought about using a plasma spray process using material equal to the base metal of the housings and then truing the housing on the miller and micropolishing it back to spec.
Then sending them off to a cryogenics facility to let them harden them.

Here is the problem I am having. It seems like the platers don't know anything about cryogenics and the cryogenics people really don't know much about plating and there seems to no one source that can give first hand advice with knowledge from all processes.

I am sure there are at least a few hardcore guys out there that have dealt with all of these processes and how they apply to engines.. any of you guys out there? I have a set of ground housings ready to go somewhere.

I don't know of anyone that has had that surface of the rotor housings replated. Even if u could find a way to get it done, I think u'd find out that it'd be alot cheaper just to buy new ones.

For what I got into the equipment now I could have bought more new housings than I would ever use. But I am hoping in the end to be able to make housings that are better than new for much less than the $450 each that new ones cost.
When you factor in the time and money people put in to making peripheral ports, or hours and hours polishing them for show only to have them become scrap metal it is easy to tell there would be a market to repair them.

Just in my rotary head friends alone I have about 15 sets lined up to do. Let's say we all go out and buy new sets at the $900 per pair, that's $13,500.
Hell, I would be happy if I could at least make a better housing for that price. I have even bigger asperations that I can get them out the door for less though.

Fortunately I love a challenge because I definately have my work cut out for me. It's a damn good thing that I have a good day job too to pay for this shit too! :eek:

Here's a pic of mine, but I want to build a rotary T-bucket once I get this project out of the way.
http://webpages.charter.net/mikeroberts/exterior03.gif

sounds like a great idea. i'm sorry that i don't know of any resources that would help ya but good luck with your project.

we had a few sets re-chromed by an electroplater - first few didnt seal that well - compressions down and the hard chrome never bedded to the apex seals. Then tried some which we honed by hand with a stone and they worked ok after a decent running in period. I don`t think the work and end cost was worth it unfortunately - would need someone to get a better finish on the housing surface to consider using in a boosted engine.

I don't have any trouble with the finishing. My polish process works great. It is a long way from Australia to Texas though. Hell, the water don't even spin the same direction going down the drain!
Did any of the housing have corner seal wear before you got started? Did the plating take care of it? I am very interested in details if you have time to cover your experience as far as what you started out with and how thick they plated it.

i think your biggest problem is clearances. you're gonna need clearance exacted to the mm to get good sealing. to get it replated and ceramic coated you have calculate for the exact thickness of the chrome and the layer of ceramic on top of it and mill the housing to accomodate them. imo, it would be very difficult to get such exacting standards. lastly, whatever you do, do not get the housings cryogenically treated!

Getting the housing to an exact original spec is not a problem. The controlled machine process is brings the wall surface to spec even if a coating is inconsistant. As long as the coating is not below spec on any part of the surface. Why would you not have the housings cryo treated?

cryo treating makes the parts stronger but very fucking brittle. cryo treated parts will crack eventually, more often sooner than later. my engine builder learned that the hard way, he lost $40k worth of cryo treated parts.

I wonder if they were not done correctly. There sure is a lot of hoopla going around about all the really hardcore race teams running cryo'd parts.

Interestingly enough there is a post about 10-15 down from this one that has info in it about redoing a housing. If you go to this link and scroll down about 1/2 down the page you'll find the info........

https://www.rx7club.com/forum/showth...hreadid=102831

I'd really like it if you sent a set there and let us all know how it turn out :)

STEPHEN

It sounds like these people are doing the same thing I am attempting. It is probably the same people that I heard rumored about after I was already pretty far into this.
Does anyone know the Rockwell hardness on a fresh housing? I took a set to a shop at lunch today that use plasma arc spray process. They quoted me for:
Kanthal- 23 Rc
420 stainless- 45 Rc
Armacor- 55 Rc
Chrome Oxide 55 RC

Chrome Oxide is ceramic and it was not cheap at all. The Armacor was about 3/4 the price. I went to the Armacor website and they claim, well read it for yourself
http://coatings.liquidmetal.com/inde...ion=technology
I am not sure about stainless or the Kanthal. When I went to a site to find out the specs on it I found that they have several variations of the material. They are at http://www.kanthal.com/
From what I can tell Stephen the only information on that thread that they gave you was a copy of an email with a name and PO box.
I would think that as many people that hit this forum that someone would know more about them.
Either way I am into this far enough that I need to make my own process at this point. I have a long way to go before I can do these for other people.
But I still want and appreciate input. I'm not spending money I can't afford to lose knowing their is a risk. But I knew going into it that it would take some perserverance or everybody would already be doing it.

That shop wants some "guinea pig" rotors so I am taking some 12a's over the weekend and prepping them. That way they can get a feel for the material. They want the nitrite off and they said that the more scored the surface the better. That is great because I can rip through it faster and not worry about smoothing. I will take pictures at the different stages for you guys to check out.

scalliwag, how much is this shit gonna be per housing?

I have to find a way that works and see how much goes into it. Right now with the numbers I just got from one shop it would not be nearly as low as I am wanting them to be. If I cannot make a BETTER than stock housing available for less than $400.00 it will not be worth it. If I can do a ceramic that will take some punishment for $500 I would be happy. I would have to have cores as well or process housings that people send me.
It is kind of hard to put a price on a yet to be finished
product though. I would love to know what the "other" guys are charging. Maybe they will see this and chime in.

You need some housings like mine then ;)

<---------------

Haha!!! I have some nasty little 12a's that will be great for the testing. But those look pretty nasty for sure!

scalli, i am in houston and have instant acces to a full facility of CNC mills and lathes and even know of some wire EDM shops too! and i can use Virtual Gibbs and Edge cam software. i also have some intersting ideas on the subject but it would take quantities to get the price down. you are right about not wanting to redo housings ....i CNC ported my exhaust ports and had them ceramic coated it would be a BITCH if i had to redo them!email me at wwm1@wt.net

That wire EDM is some cool shit. I think you would probably be shocked at how well I can do the milling and polishing process though. I would love to have access to the equipment you mention but that is one of the reasons a big shop has to charge so much. The only thing the machines I built will do is mill and polish housings. It is the coating that has me more worried right now... at least the cost of getting it done.

I would love to have access to a tool and die shop to make a mold for aluminum side housings. Then a foundry to make them. Do you have any hookups for that project?

yes i do, but i am sure you already know ....that shit aint cheap!!


MWW

Yep I know. Hopefully I can get this housing project wrapped up and take the proceeds from it and cutting rotor slots to 3mm and put the extra toward that later on. Fortunately the 3mm project was straight forward and the only hurdle there was getting the horizontal mill. At least the mill will do more than cut rotors. I just haven't found anything else to do with it yet. My garage looks like a freaking machine shop because all these machines are TOO damn big! At least that is the way my wife sees it! ;)

I used to work in tool and die repair. Did repair and maintenance in house for an aluminum and zinc diecasting company. They don't have a machine big enough to make something that size.

Boy it would sure be nice to have access (and the knowledge it takes to run) all the equipment for all the big dreams!
Hopefully after I deliver the 12a housings I can get some answers quickly. Once I get something that looks promising I will take some really tight pics.

So does anyone know the rockwell hardness of the seal surface on a new housing?

Hrm, i thought Racing beat sold Aluminum side housings already? Just a thought. Also another thing is about reusing old housings, is the shape of them. On old high of mileage housings, the aluminum part of the rotor housing , the water passages are not really in good shape. Also have to worry about checking the housing to make sure they are not warped.

What about cracks... you know, where the spark plug holes are? Is that something that would also be repaired with a new surface? If so I will have 2 in a few days because I just found out mine are cracked right there! If you ever get this going I am going to have a whole stack of damaged housings for you.

Yep, RB does sell aluminum side housings, for $1250 each. I think they need a little competition to get that price a little better.
All that has to be considered. Not every housing is going to be a good candadate for resufacing... they'll just make a good clock ;) Anyone who sends housings to me will need to check some things out before they send them.

By the way, I got a set ready to be plated today. I am crossing my fingers that the shop decides they can do them cheaper than the original quote once they run a pair and see how easy/hard they are to work with.
Keep your fingers crossed guys.

I think that is going to be a case by case basis. If you need to get a set of housings resurfaced you want to start with the best set and work your way down.
Depending on what the bottom line as far as price goes you may or may not want to risk it.
I know that I won't be testing any with cracks or anything soon. I have several good candadates right now and the testing process will take months as it is.
Of course I will be happy to do some for other people to help with testing early on. They would have to pay shipping and plating charges. I would only do that for a few people here though and they would have to be regular posters on the board so I don't throw a lot of work into their housings and never hear back on them.

Whoever I did this for has to understand that they testing and there is always a risk of it not working.
The first set I am getting done today are going to be done for free because the housings are not useable already and they are just getting a price figured out. But I will be able to finish these out and get a good visual look at what it will look like. I will post pictures.

Okay guys I got a couple to the shop to be plated. Hopefully they will get back before the end of the week on a verdict for me. I took this picture after I milled it.
I doubt you can tell from the picture but the surface finish has fine linear grooves in it. The shop told me that it was a great finish for them to work with. That made me damn happy because the surface is so hard the it takes longer with a "finer" cut.
I forgot to take a picture of that actual housing before I milled it but as you can tell from the water jacket corrosion that this is a pretty funky housing.
My ftp server is giving me trouble so you will have to click the file. :confused:

wow, that actually looks pretty decent! :) If you don't mind my asking,do you mill the full 'depth' of the housing in one pass, or do you take like 1" deep passes and spiral down?

Awesome project! :D,
Manolis

I like to see these kinda ideas, turn into something nice...

Ioften toyed with this idea, but lack the 1) funds and 2) people to correspond on such an undertaking...

I wonder if it would be also feasible for someone to make rotary engine seals etc. Theres were they need some competition... But I got to thinking again,maybe that would constitue an infridgement of copyright. Im aware of that just remilling and plating a rotor housing WOULD NOT be a copyright infrdgment. If it was all of us turning rotors would be screwed and in jail... :)

It all is done in one pass. If the entire width of the housing was not cut in one pass it would be hell to keep it even. Even the most minor inconsistency would cause compression loss.
It really would not matter as much on this phase as it would during the polish phase. That is where it is crucial that it is one level mamajamma edge to edge. It is also critical that the pattern of the housing is true or the apex seals would be "bouncing" and it would not be a matter of if but when they would break. I cannot wait to get them back. I will take a picture before and after polishing. I got my ftp site up so I can link to a closer picture of the milled surface. http://webpages.charter.net/mikeroberts/close.jpg

This link shows a bigger and better view of more of the surface. It is too big a picture to put on this page without whacking up the width of the browser windows.

http://webpages.charter.net/mikeroberts/bigmill.JPG

Scalliwag,

Great project! Keep up the good work and focus. This is the stuff of revolutionary invention. It sounds like you must become the link between the disparate technologies. It always comes down to one person with a vision and the determination to press on when no one else has the answers.

Best of luck and I look forward to progress reports!

Nat

Thanks for the support bro. Some people think it's a waste of money and effort and some are hoping like hell it works. I hate it when people use the term "reinventing the wheel" as though it is a bad thing. Take a look at the wheels on a covered wagon and thank God someone got beyond that! I ain't really trying to reinvent a wheel here, I guess I trying to retread a tire!
I got hooked up today during some of my adventures and found some people who had a foundry make tooling and actually made aluminum side plates in the eighties. They fought it into the nineties and as far as this guy knew they gave up on it. He said they kept having trouble even after "hard chroming" with wear.
I got their phone number and left a message to call me.
Unlike the Racing Beat side plates, they made theirs based off of Mazda housings so that the oiling system is not affected like with RB's. All the info I got was from the foundry. They picked up all their tooling (since they had to pay to get it all made) from the foundry a few years back.
IF they still have the stuff and are willing to sell it for a good price I will probably buy it and set it off to the side until I get this iron out of the fire at least. It is pretty interesting and with a LOT of luck all of this could go together.
I may be sending a housing to the foundry guy to get a quote on making housings. It is more morbid curiousity than anything though. If this resurfacing project works out unless I can figure out how to build a better housing it would not be practical. Maybe a housing with a better design around the spark plug and exhaust areas?
Sometimes I just think too much and I am not sure if that is good ;)
I will really be happy for our country to get through this day (9/11) without anyone doing something stupid.

Hey there, I think you're project is quiet interesting, if not valiant! I've often thought about how to resurface housings and such, and maybe even build a better wankel. If it's not too much of a bother, I'd like to share some of my ponderings with you, casue god knows we'd all like a good alternative to $400+ rotor housings and an aluminum 13B that you could pick up without an engine hoist :)

How does your polishing process work? I've thought about this a bit myself, and I was wondering if maybe you could do that by exploiting the geometry of the inside of the housing. Maybe fixing up some sort of jig that uses the gear from a rotor and a stationary gear to perform an inside-grinding operation; over-plate the inside, and run something like a rotor with 3 abrasive "apex seals" around the inside to finish the surface?

On a somewhat related note, after a bit of research I *think* the coating on the side housings is Silicon Nitride. I am led to beleive this becasue I have heard people say that lapping removes the "nitride" coating, and in US Patent #4,455,275 , which is about manufacturing bodies of silicon nitride, where it says:
"Applications which are of particular interest for silicon nitride include construction material for turbine wheels, rotor blades and other dynamically stressed parts for gas turbines, including gas turbines for vehicle operation, as a construction material for parts in Wankel engines as well as for a bearing material." But then again, the patent was granted in 1984, so it might just be a suggestion. To further confuse me, on the Rotary Aviation page (http://www.rotaryaviation.com/rotaryhistory.htm), they say that "Two-piece silicon nitride ceramic apex seals have, in the words of one summary, "a 'sprinkle' of an ingredient that raises heat conductivity", and they use 2 springs", in reference to specialized technologies that the 787B used to win the LeMans race....so maybe thats where the SiN was used.

Is it possible that the coating on the side housings is a piece that is grafted in like the rotor housings surfaces? You know how the rotor housings have that saw-tooth like pattern around the inside? Maybe the side housing has the same kind of thing... a thing plate of SiN or whatever grafted into the face of the housing, then evrything finished flat? I suppose you could find out by taking a side housing, shimming it a very small amount on one side, and then face that down so you could get a good, wide cross-sectional picture of how the coating was bonded to the housing.

Speaking of that saw-tooth bonded surface, it might be worth a try to cut/press/tear one of those things apart just to see what kind of bond it is. Maybe it would be a good idea to cut a chunk on this inner-surface material out and run some tests to figure out exactly what it is... you might have better luck trying to build that up with the same matieral somehow, rather than trying to get a different kind of plating to bond onto that.

Back to that Rotary Aviation page I quoted from earlier, it also says, in realtion to the 787B again, that "Rotor and side housings are coated with hot-sprayed chrome-carbide cermet (ceramic in a metallic array) for high-temperature wear resistance."

I hope some of this information that I have come across in my searching can be of use.

And those for Chromium Carbide:
http://www.matweb.com/search/Specifi...bassnum=BCCrCA

And for Silicon Nitride, there seem to be quite a few different kinds of SiN, and you can look them up by searching for "silicon nitride" on www.matweb.com... I did, however, come across this type of SiN that seems interesting:
http://www.matweb.com/search/Specifi...bassnum=CC0006

Also, I beleive that somewhere out there, some time way way back, there was a Popular Mechanics article that was all about how a rotary engine was manufactured... I found it on ebay but unfortuantely lost the auction. damn!

Thanks for the info. I will look into that after work. As far as my finishing process, without getting into too many details of the equipment I built mainly because it cost a lot to build (in time and money). It could be duplicated for less time and money due to the trial and error.
Using a stationary gear and other components to follow the pattern would have been plausable, but my design works more like a vertical mill.

But this is like paiting a house. There is more than one way to do it. I popped up more than one time in the middle of the night drawing out ideas. You have to be either really smart or really obsessed to get to this point. I am definately not on the smart side of the aisle!

I am hoping that this first effort in the coating process works. I will look into the processes that you mentioned and everyone will know the results.

Great work Scalliwag. Keep us posted. I did some developmental work on ceramic coatings for some gov't. projects results were promising. Let me know if I can help

I was told if I do ceramic I will have to get a diamond tool made for my machine in order to finish it.
What are some of the things that you learned during your work?

The old surface was stripped, and was the re-chromed afaik - a mate of mine organised that. The early ones had like a "pooling" of chrome at one edge if you like - I don`t know why. Like I said, we used a hone stone to create a "cross hatched and level surface". This was more just an experiment than an accurate process. Just we had a lot of housings with poor chrome, but good water jackets. One of the earliest engines my friend built was a N/A high comp 12A extend that needed to be tow started to get running. It did improve, however 1 rotor was 10psi lower than the other and had variation. I then fitted a turbo and weber style ida throttle body injection setup. Worked ok, was laggy (blowby) Eventually died by breaking an endplate. Sripped it and found areas where apex seal had only just been touching housing surface. I rebuilt with new housings, revised porting and low comp rotors - heaps more responsive. But I reckon If you could get a machined surface on housing - should work great - I mean trying to level with a hone stone is fairly primitive.....

Yep that honing process would worry me. Trying to keep it consistant so the apex seals did not chatter would seem to be the hard part. Any little bounce would lose compression.

I wonder if you could help maintain consistency by stacking 2, 3, or more housings together and honing them all at the same time. Of course, the ability to do this would depend on the machinery you have at your disposal.

BTW - I love the line "I'm not trying to reinvent the wheel, I'm trying to retread a tire!" :D

The biggest problem I had to overcome was not the honing, grinding, milling, or polishing. Granted that hard plate was a problem in itself with tooling. But it was keeping the shape precise that was the real ass kicker.

This is an update:
I still have not got my housings back yet. :(

As far as these side plates people go, here is the scoop. I talked to the people that own the tooling. It turns out that they took their tooling to another foundry because of problems in the castings from the original foundry. This call got really interesting. It turns out that these guys make generators using rotaries! They have even made four rotor engines that are peripherally ported.
They still have not worked out all the bugs in the side housings and he said that yes these are direct matches of stock housings as far as the oiling system, tranny mount, etc. He said that there is about 6 hours machine time after the plates are finished and that is was costing him about $250 for each casting.
I damn near begged him to cut me a deal on some at any stage and he said that he would call me when they ordered their next batch from the foundry. He did not set me a price though. :eek:
Back to the rotor housings though I am going to get pricing to tool up for finishing ceramic. It will cost $180 more in plating and the tooling will cost me out the ass but after reading the link that "CrazyDude" posted http://www.rotaryaviation.com/rotaryhistory.htm
Go to the area titled "ROTARY HISTORY 7: THE ONE THAT WON IN '91 ". The "hot-sprayed chrome-carbide cermet" is the ceramic spray process and that car won the 24 hour LeMans and when they yanked the motor apart they were stunned at the lacked of wear.
I don't know about you guys but if this process is that much better then the extra cost would be worth it.

Of course I am going to try the other process first and see how that does. If it's tougher than stock and works with all the apex seals I will be happy.... at least for a week! Ceramic will happen though.

Oops, I double posted!

This is only my opinion (I don't know much about materials science YET, thats what college is for I suppose), but I would think you'd be able to achieve the best result by building up whatever material that is on the inside face with more of the same, and then cut/grind/polish it down to spec. Maybe the 3rd gen housings already have the Chromium Carbide coat... I have been told that 3rd gen housings last longer than non-3rg gen housings.

A mazda reman comes with re-surfaced rotor housings doesn't it? Maybe if someone talked to Mazda we could get a housing reman program going... just trade in your old housings + some $$ for resurfaced housings? I remember reading somewhere, though, that the special grinding machines are located in japan.... but...maybe if you approach them seriously about it, they would help you out and share some info on these resurfacing technologies with you.

I mean, the Mazda people usually arent a bunch of dickheads to enthusiasts (except when it comes to window switches!). Maybe this is the kind of issue that could/should be raised at SevenStock, where Mazda officials who support the rotary are present.

Back to more coatings and such... this website might be of interest: http://www.toyo-at.co.jp/kaisya/etop.html
They talk about Mazda seeking new super-hard coatings for engine parts, and coincidentally, that company does seem to offer a whole lot of different coatings, check it out under the "Hard Coating" part of their english site: http://www.toyo-at.co.jp/eindex.html
I think that company is actually owned by Mazda, so its very possible that one of the grinding machines on their site is exactly what was used to re-finish rotor housings.

I also came across this VERY complete site: http://members.rogers.com/sofronov/C...da/Rotary.html
which seems to have information on EVERY mazda rotary engine! Things of interest....
-It is too long to copy + paste here, but DEFIANTELY go look at the page about the 12A motors... it dicusses how the "Sheetmetal Insertion Process) was first used for the 12A's; this is the jagged-edge sidewall that you see in the housings!
-The chroming proccess that is used on the housings is a "pinpoint-pouros-chrome", which, as it sounds from reading that page, is a surface that is designed to have tiny holes in it so it retains oil that is sprayed into the chamber.
-FINALLY! The nitride coating on the side housings is SPECIFALLY named: Fe-C-N. I can't find any info on this on MatWeb though :(
-About the R26B, the site reads "The rotor housings and side housings were Hot-Ceramic Coated" .... so I guess the side housings can benefit from this treatment too!

It might be worth finding a junk housings and cutting them up and looking at them under a microscope to determine how thick each layer is.

I hope this info has been of help!

Form what I have been told Mazda uses an insert sleeve kind of like sleeving a piston cylinder on the refurbed housings. I don't want to try to figure out how to do that. The "hot ceramic" is a spray process.

you guys need to get your terminology straight. rotor housings and side housings are different. i have heard rumours that mazdausa sends side housings to japan to have them resurfaced. redoing the side housings is no problem mazdatrix has a page showing how they do it.
nobody resurfaces rotor housings, at this time. it is a lot cheaper for mazda to just use new ones. economically speaking (and for them warranty proposes too). also keep in mind the cost of new mazda side housings, they are close to $250 each.

mike

Mazda doesn't redo rotor housings. They just throw them away and use new ones.

You might be thinking of the process whereby they make new rotor housings... they start with a steel sleeve, form it into the proper shape, and then cast the aluminum around that. then, all sorts of wonderful machining operations, and then they plate the inner surface.

I'm not that sure that we need to get our terminology straight as maybe you may want to pay closer attention to the posts. When we are talking about rotor housings we are talking about rotor housings and when we are talking about side plates we are talking about side plates.
The thread expanded to side plates as well because of the people making aluminum side plates I ran into while researching out the processing options for the rotor housings.
Since the Mazda side plates are made of cast iron, the aluminum ones that these people have been working on are a better option. They sound like they may end up costing more than the ones made by Racing Beat, but these are Mazda correct plates that kept the regulator fitting in the design unlike RB's.

mr dad used to work doing tool and die, and my uncle owns a tool and die shop
i never even thought of them for these uses :D

Does anyone think it's possible to make side exhaust side housings IF someone makes aftermarket side plates? We could then benefit from the increased exhaust port area that the RX8 benefits from. That way we wouldn't have to worry about fitting RX8 engines to our old 7's.
Oh, and motorcycle forks sometime have silicon nitride coating on them (GSXR 1000 & Ohlins etc.) because it reduces "stiction". Stiction is the force that keeps things from sliding past each other initially. Like when you a wet suction cup down a piece of glass... it doesn't want to move at first, but once you get it started it slides ok. A friend of mine rebuilt his 13B and sent the plates to one company to have them lapped, then he sent them to a coatings place to have them re-nitrided. I can probably get the info if it would help. There are also companies that nitride motorcycle forks for racers.
Don.