coatings and treatments

[kfcpork]

so after stumbling threw the resurface/re hardening thread it made me realize im still very very dumb. anyone want to give me an explanation on why you nitrate plates when reconditioning them? also would it be a good idea to do the same to rotors?!? what about cryo-ing (crap grammar i know) plates and rotors or shot peening/wpc treating them?!? has anyone on here tried any of that with good results or cryo-ed seals or even wpc treated them?!? any clearance issues afterwards? food for thought i guess after i saw the re hardening thread it made me wonder so seeing what you guys think/know what works and doesn't

[rgould]

1) the factory nitrate is only about .010 deep into the sideplate surface so when you resurface a badly worn plate you cut through the original harding which leaves soft cast iron for the side seals and corner buttons to ride against.
2) the rotor does not ride against the side plate so it does not need hardening. Ceramic coating is a better choice to help keep the excessive heat on the rotor face and to help control oil temps.
3) I have been involved with cryoed brake rotors on all out race cars and for some reason they last longer than ones not cryoed so it does something good to the metal.
4) shot peening uses small steel shot like steel bbs to beat the metal surface to remove internal stresses.
5) as in any engine rebuild you have to be mindful of the clearances on all the internal parts going into the build.

[kfcpork]

i had forgotten completely about ceramic coatings, and from what i've been reading the more parts you can cryo the better. still a noob when it comes to rotary motors waiting for a few books to come in the mail so i don't sound so challenged but i think it would a good idea to wpc treat the plates after resurfacing them then nitrate them. feels like money spent in a good place for some extra insurance. as far as clearances go do people make plus sized corner seals and buttons to make up for that treatment?!? (NOOB-ISH I KNOW)

[RETed]

Originally Posted by rgould

2) the rotor does not ride against the side plate so it does not need hardening. Ceramic coating is a better choice to help keep the excessive heat on the rotor face and to help control oil temps.

Be very careful about this...
There is a right way and a wrong way for these coatings.
In general, metal sections are used to conduct heat (away).
Putting coatings on the wrong surfaces can increase (internal) heat (into the cooling and oil systems).
Mazda engineers have documented that the rotary engine oil system takes care of 1/3rd of the heat (dissipation) from the working engine.

3) I have been involved with cryoed brake rotors on all out race cars and for some reason they last longer than ones not cryoed so it does something good to the metal.

It's the conversion of martensite and austenite crystals within "steel" alloys.
http://en.wikipedia.org/wiki/Cryogenic_hardening

4) shot peening uses small steel shot like steel bbs to beat the metal surface to remove internal stresses.

You should remove the word "internal".
This is more a surface treatment, and it converts tensile stress to compressive stress.
It is also not recommended for critical clearanced surfaces.
http://en.wikipedia.org/wiki/Shot_peening


-Ted

[rgould]

as far as clearances go do people make plus sized corner seals and buttons to make up for that treatment?!?

not real sure on the plus sized parts except for wider apex seals but thats why i spent the money and had an expert build my current 13b rew ( engine builder Rick Engman )

[rgould]

Be very careful about this...
There is a right way and a wrong way for these coatings.

In general, metal sections are used to conduct heat (away).
Putting coatings on the wrong surfaces can increase (internal) heat (into the cooling and oil systems).
Mazda engineers have documented that the rotary engine oil system takes care of 1/3rd of the heat (dissipation) from the working engine.

I'm running Ceramic coated rotors on the recommendation of my engine building
(Rick Engman)

You should remove the word "internal".

Point taken

It is also not recommended for critical clearanced surfaces.

I was not recommending this surface treatment. Yes it wrecks a finished machinied surface. I have had to remachine shot peeded race piston engine parts it's sucks

[kfcpork]

all very good advice i had forgotten about the fact side plates and what not are machined surfaces much like a crosshatch in a bore of a piston engine. but keep opinions/experiences going this is a food for thought thread so one day noobs like me going threw a first rebuild can see different options and choices and do it right the first time. i've had to fix plenty of mistakes in the subaru game because people don't listen to the simple facts laid in front of them still am atm im welding up a new header for my buddy becuase he thought some cheap chinese copy of a greddy header was just as good as the real thing and after less the a hundred miles the flanges have warped and welds have cracked FML. point of that stroy i guess if give what ever you can so people dont make mistakes like these and give up on rotaries

[j9fd3s]

the coatings are an interesting topic. thru the history of the rotary engines mazda has tried several iterations of coatings on various bits, the ones that offer a good benefit for the cost have made it into production engines.

with the side irons the R100 engine was the first to have iron side housings, and until the end of Rx3/Rx4 production in 1978 the irons are just natural. the finish isn't mirror smooth, its fairly rough, as it needs to hold oil.

with the advent of the Rx7 in 1978, the irons are gas nitrided. this gives the iron that grey color. the nitriding wears much slower than the bare iron something like 10x, and it also reduces friction. Mazda has published info on this, if i run across it, i'll post it up.

the RB26 engine in the 787B uses a ceramic coating, both to reduce wear and probably lower friction. i have no info on this, really.

i know next to nothing about the coatings for bearings, although since a rotary bearing is just a bearing, i don't see why it wouldn't work, as long as you make sure you have the clearance AFTER the coating is done.

rotor face coatings i am undecided about. there actually is some conflicting info on the subject. both NSU and Mazda show that the rotor face temps actually need to be rather hot. as you can see in the attached graph the NON cooled aluminum rotor (something mazda didn't try until the late 80's) actually does not run hot enough.

this may give an opportunity to have fewer losses into the oil, and thus make the engine more efficient, along with loosing the oil cooler. pic #2 is the heat balances of the NSU engines. note the heat into the oil is much less than the Mazda already.

however Ted's point is also valid, the heat has to go somewhere... and the NSU engines have different construction.

mike