Ok enough with the long and boring posts , who has seen the below link? (I previously posted it on the rx7forum but not here)

http://media.mazda.ch/dossiers/Wankel/Wankel%20E.pdf

Some excerpts from the paper:

"The inner surface of the rotor housing consists of a chrome-molybdenum alloy plating".

"Trochoid Surface - the surface against which the rotor moves. It consist of a chrome-molybdenum alloy. Molybdenum is one of the only materials that does not suffer from chatter marks in engine applications".

"Port Liner - Port liners "line" the side exhaust ducts of the new Renesis engine. The basic material of the port liners are made of aluminum titinate, the stoichiometric compound made of aluminum oxide and titanium dioxide. This material is characterized by its low thermal conductivity, extremely low thermal expansion coefficient which makes it very temperature resistant, and it is highly porous. The porosity makes this material very useful in engine construction. Its porosity is a result of the cooling process, during which critical interior tension brings about the creation of microscopic cracks, which partially close again when the material is heated".

Does anyone have any additional info on chrome-molybdenum and aluminum titinate?

Brian

 

i dont know about the titanate stuff but i do remember about 14-16 years ago in a JC Whitney catalog they sold an engine additive called 'Moly' which was an 8oz bottle of an oil additive containing molybdenum. If i remember correctly they claimed it acted like a shield of microscopic ball bearings between moving metal parts reducing friction thus increasing engine life and so on. My guess is that they somehow permanently incorporated the properties of molybdenum into the chrome alloy giving it a natural friction reducing ability in turn giving new meaning to the term "holy moly!"

 

I'm pretty sure chrome-molybdenum is what is used to make mountain bike frames. Although aluminum frames have been more popular for the last 10 years or so, "chromoly" frames are making a bit of a comeback. My newest bike is a 4130 chromoly alloy.

 

Molybdenum is also used in the engine on the Z.

 

Zoom- Zoom... What just pasted over my head???

Oh yeah, this post


Cool stuff to read and learn, but out of my league.

Roachman

 

Chrome molybdenum and the molybdenum coating used by Nissan, and several others, including GM, are different. The latter is for friction reduction while the former is for wear reduction.

 

Whhoa! Good info find Buger! Admittedly, I didn't read the whole thing yet, but it looks like mazda engineers have taken a lot of measures to allow the engine to hold together even better than past rotaries.

It will be the first new one I'll have owned, so if I take good care of it, I'm hoping I can easily get the 200,000 miles+ I've heard others claim. Sound reasonable?

 

The rotor housings have always been made this way

Any one who has ported the exhaust or made bridgeports can attest to the toughness of the housing materials.

The chrome surface is what the apex seals run against. The molybdenum is underneath the chrome to provide a strong base between the chrome and the aluminum.

The ceramic coatings insulate the side housings from excess heat transfer and to provide a nice smooth path for the exhaust to follow.

A smooth path increases power and expells more exhaust.

 

Hi MyT13B,

I was hoping somebody would have more information on what the previous peripheral housings had on them. Do you have a link or other source that quotes the use of chrome-molybdenum alloy for the peripheral housings? It sounds like you are not describing an alloy of the 2 metals but rather 2 different layers of them fore previous rotaries?

I have tried finding out what the coatings on previous peripheral housings were made of. I know that the 4-rotor that won lemans had a chrome-carbide based cermet. I also assumed that Mazda used chromium carbide or chromium nitride for the inner surfaces of the previous peripheral housings. Mazda used to be Toyo Kogyo and the "Toyo" from Toyo Kogyo is who I thought did the chromium carbide or chromium nitride deposition for previous Mazda rotaries. (http://www.toyo-at.co.jp/eindex.html)

I also hadn't been able to find anything regarding the material used for the exhaust liners. Do you have the links that mention the use of the chrome-molybdenum alloy and aluminum titinate for previous rotaries?

Thanks, Brian

 

I have seen it first hand while machining the housings myself.

Mazda has also used the ceramics in the old style exhaust ports for the same reasons..........


It takes alot of patience and a good strong tungsten cutter to even touch the rotor housing ports, especially to cut throught the trichiod for a peripheral intake port.

 

I think we have a misunderstanding on whether old housings were coated in hard chromium or a chromium-molybdenum alloy. I was hoping that you had another reason for saying that previous housings had the chromium-molybdenum alloy. It might be rather hard to tell the difference between chromium and chromium-molybdenum just based on your perceptions of its hardness and by sight?

I know in 1974, Mazda started using it's SIP (sheet-metal insert process) and the chromium electroplating was put on the sheet-metal not the aluminum.

I also know that pinpoint-porous chrome plating was used on the 12b and a new process called MCP (Micro-Channel Porous Plating)
was used on the chrome plating of the 12b turbo.

Mazda has used a cermet (ceramic-chrome-carbide alloy) in the lemans winner and in the hydrogen running prototypes. The ceramic allows the alloy to have very little thermal conductivity which is great for the rotary but it is also very cost prohibitive.

I still have not found any reference to Mazda using a chrome-molybdenum alloy on previous engines. Perhaps someone out there may have a reference?

Brian

 

Hi KKMmaniac,

I would think that 200,000 is reasonable if it is taken care of. The NA engines have always been very reliable. The renesis only has 3 small holes that the apex seals have to ride over on the peripheral housing now. The oil injector hole, and the 2 spark plug holes.

There used to be a larger hole for the exhaust port but of course that is gone now.

 

I don't really know what all of this does, but it sounds pretty cool. And anything that makes the rotary better is fine by me.

 

I don't know if this helps, (not specific about the chrome composition) but it sorta shows what Buger is talking about. The following is from a book by Jack Yamaguchi (Road & Track journalist among other things) "RX-7 - The New Mazda RX-7 and Mazda Rotary Engine Sports Cars" which introduced the 2nd gen. RX-7. Excellent book by the way!

 

Sorry, after realizing the first attachment was illegible, I changed the res on that one, and added this:

 

Buger, this IS the sheet metal insert. It is plated with porous chromium to help hold a small amount of lubricant for the apex seal.

The cast iron apex seals in my opinion are ok for public use and low rpm sealing.

For high rpm usage these cast iron seals have way too much inertia and have a tendency to chatter at high speeds. The two and three piece designs also dig into the side housings and wear them beyond the limit of resurfacing after 100,000 miles of use.

I use a special aluminum carbide apex seal that is like the old way that is a one piece seal. For a high powered rotary there is nothing better. It also save you when it comes time to freshen the seals, much like doing a ring job on a piston engine.

Cast iron seals would never see 17,000 rpm without failure, too much intertia there and chattering is bound to occur. A 1974 engine could see that much rpm if they did not have the exhaust port in the rotor housing. At about 12,000 rpm you get bits and pieces of your apex seals out the exhaust ports no matter what they are made of.

 

Hi MyT13B,

I had a feeling you were referring to the two different layers of materials as being the same as the chrome-molybdenum alloy but I don't think they are.

According to dictionary.com, an alloy is "A homogeneous mixture or solid solution of two or more metals, the atoms of one replacing or occupying interstitial positions between the atoms of the other: Brass is an alloy of zinc and copper.

I don't think that Mazda would call two different layers of different materials an alloy of the two materials.

Whatever the case, I haven't read that Mazda used a different material on the apex seals. The aluminum carbide apex seals are interesting but are probably much more expensive I assume?

I read that the Mazda that won Lemans had ceramic apex seals (silicon nitride) but for stock applications, the cost is probably higher than Mazda wanted.

Brian

 

Nice Scans KKMmaniac, the print on the first one was a little small but I could still read it.

Brian

 

i've also heard some nasty things about some of those harder ceramic seals: in 3mm form, they seem to chew up housings rather nicely, something which i don't think would do too much good in the (probably far FAR more than) trillions of revolutions the RENESIS would see in its target life.

 

Buger,

The apex seals I use are much more expensive than the stock ones. Compared to the ceramic ones they are a real bargain but don't last as long.

There is no point in arguing about the housing since you have never seen one.


The trichoid sleeve is made of the alloy and is then plated with chrome, end of story....


No matter what things are made of, you can rest assured that things are drastically improved over previous designs while still being affordable.

 

MyT13B,

You're right that there is not point in arguing although you're assuming that I have never seen one seems like you didn't want this to end?

Whatever the case, I think most all of us here want to see if we can put on a few hundred thousand miles on a renesis.

Brian

 

just a friction reducing coating. The pistons I'm using on my integra have it on the sideskirts.

 

on your SIDE SKIRTS??? maybe i misunderstand what you mean...

anyhoo, an alloy composed of mostly these two metals, molybdenum and chromium, could take on a few different arrangements, and when you mix in other elements in lesser amounts, it doesn't change the name (i dunno what the thresholds are, but usually only the largest one or two components of an alloy are named... aluminum, even when only 40% (i dunno if that's by mol or by gram) is simply called an "aluminum alloy")... AND there could be a few different uses for such an alloy, as it may have a few properties worth exploiting in strictly different uses. take cast iron (steel), for example. it's quite heat resistant, fairly strong, and cheap. this is why it (still) proliferates as a common alloy. also note that by simply changing the method of manufacture from casting to forging, you end up with a completely different "sort" of metal. all the same molecules are there, the name (steel) is the same, but the crystalline structure and properties are different: it's less suseptable to heat, is "lighter" (you can use less of it), stronger, and more brittle. not only that, but it has a denser crystal matrix and is much less porous.
blah blah blah, i'm a dummy... sorry to go on and on.
in short (if you just skipped to here it's okay) one metal usually doesn't have one form or one use.

sorry, my metalurgical knowledge is lacking with regards to your question Boogs, but it seems to me you knew the answer (or had a strong suspicion) before you asked?? :p heh heh...

 

yeah, the sides of the piston. Often called sideskirts, maybe because they extend down around rod, kinda like a skirt.

 

er... you mean the 12A and 12A turbo, right?

The 12A was used in the SA/FB (1st generation) RX-7 in all models but the North American Only 1984-1985 GSL-SE. The Japanese market got a 165 HP turbo 12A option.