Mazda 13B / 12A (Wankel)

Mazda's Wankel rotary — the 12A and 13B — in the RX-7 and RX-8.

⚑ Nothing else in this catalogue works like it, and almost no ordinary diagnostic instinct transfers. There are no pistons, no valves, no camshaft and no timing belt. A triangular rotor turns inside an epitrochoidal housing, and the seals that do the work of piston rings run across the housing face rather than around a bore.

Compression testing needs a rotary-specific gauge, because each rotor face produces three pulses per revolution and a conventional tester reports the highest one. A conventional compression figure from one of these means nothing, and it is the commonest way a bad engine is passed as good.

Apex seal wear is the failure the family is known for, and its symptom is a hot-restart problem: the engine starts from cold and refuses when warm. Flooding on a short run is the other classic — a rotary stopped before it warms will not restart, and that is behaviour rather than a fault.

It burns oil on purpose. Oil is metered into the combustion chamber to lubricate the seals, so consumption is designed in and checking the level is not optional maintenance. An owner told their engine should not use oil has been told about a different kind of engine.

The 13B-REW is sequentially twin-turbocharged and its vacuum control system is notoriously complex; a boost complaint on an FD RX-7 is a hose and actuator question before it is a turbocharger one.