[prsutherland]

A Wankel has seals attached to the rotor that rub against the wall of the chamber. This engine only has three points on the chamber wall that touch the rotor, so the seals can be installed on the chamber wall and it is significant easier to cool and lubricate a fixed seal rather than a rotating seal.

[dv_dt]

Wouldn't there also be seals on the two faces of the rotor too?

[ansible]

> Wouldn't there also be seals on the two faces of the rotor too?

Yes. However, the apex seals of the Wankel are the most troublesome, from what I've read about the RX-7/8.

[sitharus]

As I understand it from friends who're in to rotary engines, the biggest problem is the spark plug hole. The seal - which is being forced outwards by rotation - will fall in to the hole slightly and then wear against the edges of the hole as it rotates past. This gradually increases blow-by and reduces efficiency until it no longer seals at all.

This design has a smooth surface against the seals at all times, and they can be lubricated directly.

[pengaru]

That is not the primary source of wear problems on Mazda Wankels.

What you're describing is a challenge on peripheral port (race) engines where very large intake and exhaust ports must be bridged by the apex seals, and in the pursuit of performance their radius is often less than ideal making the transition onto and out of the port area more abrupt.

The spark plug hole however is relatively small and circular.

High-mileage Mazda Wankels typically require overhauling because the side seals become seized in a compressed state (their springs are meager segments of ~sinusoidal wire, and the motor burns oil by design causing excess carbon/coking clogging them up), resulting in excess blow-by and unintended oil burning. Once the side seals go, the combustion gases start reaching the oil control rings, baking their soft interior seals into brittle plastic and it's all downhill from there.

source: former rx-7 enthusiast with multiple diy engine rebuilds in his past.

Edit:

BTW something that's often misunderstood about Wankels is that the rotor turns lazily at 1/3rd the engine RPM. So despite it being a "high revving" engine, there isn't actually that much centrifugal force acting on the apex seals at conventional engine speeds. The pain point in this department is the stationary gears responsible for converting that 3X eccentric shaft speed into a mix of orbital and rotational motion at the rotors.

[smokelegend]

Insane power

1000+Hp Turbo 4rotor AWD [All-Wheel-Drive]

https://m.youtube.com/results?search_query=4rotor+turbo+1200... There's definitely a market for rotary engines, time will tell how this new form takes shape.

[sitharus]

Thanks for the clarification! My friends were in to performance so I guess that’s what they were referring to.

[deelowe]

The same seal that contacts the rotor likely seals the face as well. That's how wankels work.

[mannykannot]

The 'seals' section in this article suggests that wankels need separate apex and side seals:

http://what-when-how.com/automobile/wankel-engines-automobil...

See also Pengaru's comment about problems with side seals, specifically:

https://news.ycombinator.com/item?id=25451923

[tsomctl]

So what, you have oiling or cooling passages immediately behind the seal?