(i posted this same thread in the "general rotary tech" section, but decided to post in this section too)


Today i was at my shop and decided to feed my curiosity. last year i swapped an S4 13b into my 82 rx7 to replace/upgrade my old worn out 12A. The 12A had ~100k on it but i could feel it was getting weak and took some encouragement to start, either way i had no intention of doin anything with the motor.

Upon tear down, I found the irons to be in great shape with minimal side/corner seal wear, and as expected the housings are junk with 1/4-1/2"of flaking in multiple areas though out the perimeter. There were also carbon/burnt streaks across the chrome around the leading spark plug holes as well as large burnt areas above the exhaust ports. Both rotors covered in black sooty carbon on the combustion faces (except the 1st 2 inches of the leading edges, which were clean). Further inspection showed that almost all of my corner seal springs were dead (corner seals moved freely, but sat flush with the surface of the rotor..springs werent doin a damn thing) as well as 3 or 4 apex seal springs that were virtually flat, while 1 still had an almost "new" shaped arch to it

lastly, ive torn down 4 other motors (3x 12A's and 1x 13B) before this one and i dont recall seeing this in any of them... all but 1 apex seal looks like theyve been heated to hell and back, definate discoloration and bluing





is this "normal" to have apex seals showing this kind of coloring? if not what would be the cause? I never overheated the motor, it never ate coolant, motor had a shimmed OPR @80-90psi

 

To me the flattened springs and seals that show heat damage indicate very high oil temperatures or insufficient oil cooling to the rotors somehow.

The scoring on the sides of the apex seals indicate to me that the rotor was overheated closing the seal slot as well.

All the seals /springs in the rotor are cooled by the rotor which is in turn cooled by the oil squirted inside.

Extreme cases of high egt and/or exhaust backpressure can cause this as well as the normal oil cooling can not keep up with the rotor heat loads. All that dark soot in the engine doesn't sound like high egts to me though.

If this was a later motor I would suspect a stuck oil thermal pellet blocking oil flow into the rotors.

Do you have the insufficient "beehive" oil to water heat exchanger or the later upgraded oil to air heat exchanger?

 

this was the original motor in an '82 chassis. still had the proper oil cooler up front, no behive here. the motor also had a modded oil pressure regulator that would bypass at around 100psi. engine also was running a relatively low restriction exhaust (full RB system, header to muffler) and was being fed by a weber style carb, plus i was running a heavier premix ratio to boot.

when i got the car years ago, the only mod was the exhaust, everything else was stock. In my hands, it recieved all the other add-ons... carb, MSD's, oil pressure regulator, convert to premix, and switched to mobil1

i cannot speak for the prior owner as per how they treated the car or what may have happened to it, but the 10k miles i put on it were relatively modest with the occasional spirited run, but never did i let the temps get outta control

 

i've never seen anything like that, although the RB catalog would imply that the rotors were too hot....

since its galled a little, the oil film broke down, but that can be from the heat, so maybe its a stuck oil squirter?