Rx8 rotary engine teardown | Overheated Rotor housings

We have a deep admiration for our rotary engines as they possess a remarkable ability to rev high, produce pleasing sounds, and harmonize perfectly with the well-balanced chassis of the Rx8.

Our latest Rx8 rebuild project was one that ran well until it didn't. Too much heat, too little heat rejection from the radiators.

The radiator in the Rx8 is adequate when all other components are working well. Remove the lower pan (or crack / dislodge it) and the engine will run hot until the rotor housings can't take it anymore and the apex seals bend and coolant gets into the combustion chambers and no longer starts when warmed up.

The rotary engine is a good design, take care of it and you'll get years from your high winding motor. We have race motors still running after 20 years of track duty. It is all in the details.

This engine / car came in with one of the worst slow oil leaks I've seen in a long time. Long live our ultrasonic cleaner...

Once we get all the components off the keg and ready for the Ultrasonic cleaner, we see a lot of wear & tear on the wiring harness and corrosion on aluminum components. 

Our extensive experience has taught us that the way the motor disassembles reveals valuable information about the number of overheating episodes and the overall strain on the engine.

I like to remove the long tension bolts manually, this shows me how much stretching went on when the motor was running hot. Any good engine builder will know what I am referring to. It is all about 'feel' when it is proper vs. when the motor is structurally beat to hell.

Oil control rings, what can they show us? The oiling system is critical on the rotary engine, 40% of cooling happens through the center of this motor. The oil control rings and their seals keep the oil out of the combustion chambers. When I see the oil has left components with a gold color when it should be its more normal cast look that tells me that the oil ran really hot for a long time. I like to pull the oil control rings out and notice if they fall out or not. After pulling them out, checking the oil control seals and see how many are split / broken. This motor had 3 broken, this meant that the motor smoked a lot allowing oil into the combustion chambers and out the tail pipe.

Apex seals, factory Mazda ones tend to bend easily when they are over-heated, this is where you see the outer edges of the rotor housings scored, they got hot. Many times they won't break and they will remain fairly straight, do damage to the rotor housings and the motor is toast.

As evident in the image on the right, the ultrasonic cleaner is an essential tool for a successful engine build. We have a little bit of cleaning to do before reassembly, Get it right, make it last.

For starters, this motor will need:
Rotor housings
All new seals and  springs
Oil control rings, seals and springs
New rotor / main bearings
Master gasket set
Replace 3 wiring harness connectors
New clutch / pressure plate / throwout bearing
Belts / hoses
New oil lines
Radiator / overflow tank
Clean oil coolers, straighten fins, check for leaks, stainless steel mesh screens

Next up is measuring rotors, side housings, e-shaft to specs and of course which side seals are needed before we start reassembly. We will test the fuel system / injectors before we start the build.