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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
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12-06-2011, 06:54 PM
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