This may have been covered before but I tried to search but found nothing. Why are our housings just a coated piece of aluminum instead of making them cast iron like a piston head. I mean it would be way heavier, but I think it would be stronger and since it would be cast iron it would have the same heat expansion rate as the "irons" already in the engine. And on that note, would piston ring material work for an apex seal? If it's strong enough for a piston would it hold up to rotary abuse? If that's a yes it probably would eat the housing's coating right.

Just curious!

 

I would imagine the thermal conductivity of aluminum plays a role. Aluminum transfers heat about 2-3 times faster than cast, transfering more heat into the coolant?

 

the SAE papers tell the story why the rotor housings are aluminum, its because they have a high heat load in the combustion area

from the NSU wankel spider paper, its a one rotor so the rotor housing is in the center



and from Mazda's 10A paper



as for the piston ring question, the side seals ARE piston ring material. the apex seals aren't very far off, they are iron, but with a hardened top.

its hard to say what a regular piston ring material apex would do, but without the hardened wear surface, it would probably wear quickly?

 

^^^ Yep^^^^ good stuff

 

actually they are wanting to used aluminum side irons in the new 16x.. so it seems there getting away from cast iron all together..

 

The original 10As had aluminum side housings as well. I don't know if they had chrome plated sheetmetal inserts like the rotor housings or if they were coated like Porsche cylinders.

Interesting tidbit: Apparently, some Chinese military vehicles use Wankels with iron rotor housings. The engines supposedly last 25,000-80,000km between overhauls. Information on these engines is sparse, probably because of the twin problems of military secrecy and patent infringement.

Kinda like the AutoVAZ (Lada) Wankels that were, suspiciously, 604ccx2. Very hard to get info on them, although someone did post pictures of them on one of the other rotary forums. It looked... weird. Like Mazda-but-not-quite.

 

Mazda Wankel engine - Wikipedia, the free encyclopedia

According to wiki- 10a The rotor housing was made of sand-cast aluminum plated with chrome, while the aluminum sides were sprayed with molten carbon steel for strength. Cast iron was used for the rotors themselves, and their eccentric shafts were of expensive chrome-molybdenum steel[citation needed]. The addition of aluminum/carbon apex seals addressed the chatter mark problem.

 

Thanks j9fd3s. I've been wondering exactly how the housings are made and your info says "permanently molded". I'm still on the fence as to whether it is actually a permanent mold process or die-cast or a marriage of both. The internals of the water jacket say die-cast but the large runner vestige at the bottom of the housing is not consistent with die-cast. Also, there seems to be a lot of gapping in the mold and none of the familiar vent tracking of a permanently molded part. Porosity levels are very low. Not consistent with die-cast.

I'm beginning to wonder if they might be made by an early form of semi-solid forging. I don't know.

 

that is for the cosmo 110 version of the 10A, the R100 reverted to the iron side housings that we're familiar with, although pre Rx7 they are "induction hardened" like it says in the SAE paper snippet

don't forget the very early 10A's have the chrome sprayed right on the aluminum, and then they later added the steel liner, and then added the "teeth" in the current Sheetmetal Insert Process (SIP)

there used to be a youtube video of them making an Rx8 rotor housing

 

 

lol this is gettin goood! nice info guys!

 

and we all know how durable those 10A engines were..

fix for the apex seals is easy, move away from the brittle cast iron seals.

i'm sure the argument will arise again that mazda spent millions on R+D for the apex, side, corner and soft seals but most of that was spent over 40 years ago! most engines i build nowadays don't run OEM soft or apex seals.

 

I thought 10As used carbon-aluminum seals like all of the other thick-seal engines.

Have heard stories of people making cheap race seals by pulling apart dead pre-74 12As and milling them down to 3mm for use in later rotors.

 

i was referring to the later model engines, no one runs the early engines anymore unless they are keeping the car original for nostalgia sake. the carbon seals weren't aluminum filled like some of the race carbon seals are.

 

the 10A's aren't unreliable because the rotor housings were aluminum.

 

the housings survived just fine, the housings weren't the issue.