What causes the apex seals to “blow”. Ok, so your engine is running smooth and then what?

 

My guess is either the seal finally wiggles out of tolerance after a long and happy life, or it fails due to previous abuse like heat damage or dirty oil. All machines will wear out of spec. eventually even under ideal conditions.

It's going to happen sooner or later

 

It can happen real quick when there is no oil in there. So I would say heat and oil cause them to go. Also just life, they get tired, kinda like rings on a piston engine.

 

Or they catch an edge on the flaking and scarred surface of oil-starved rotor housings and are subsequently unceremoniously spat out the exhaust port.

Or if run on dirty oil that gets topped up but never changed. Crud builds up in the seals causing them to be unable to float freely on their springs. Poor compression is one result, but uneven wear and tear on the rotor housing is another, providing more places for an apex seal to catch an edge. That's my theory anyway...

 

detonation hasn't been mentioned yet

 

Yup, that's a big one--- especially with boosted engines. N/As rarely if ever have that problem unless a) the rotors are carboned up after years of running dirty oil and/ or worn oil seals, which can cause pre-ignition; or b) the engine is running unusually hot--- in which case if the detonation doesn't get you the warped housings and leaking water jacket seals will.