Compression loss. Most common is apex seal failure, which generally destroys everything in the same common chamber (front or rear) and you wind up with zero compression on one rotor, making it effectively dead weight, while the other rotor remains healthy and functional. You can also have compression loss from a single apex seal breaking or cracking, which decreases compression on 2 of the 3 faces in that chamber. This is a bit harder to diagnose with a piston compression checker or an audible poorman ’s test. Finally you can have a side or cornerseal fail resulting in a smaller loss of compression which will seem more at random than an apex seal failure. You usually only see side and cornerseals fail as a result of improper rebuild/assembly or port work. Compression loss can result in hard starting, a rhythmic cranking sound, sound of an old lawnmower when started, total loss of power, lack of ability to hold a good idle or any idle, severe vibration below 2000rpm, excessive backfiring (due to unburned fuel in the exhaust), erratic or rhythmic vacuum readings, and lack of ability to build much if any boost. Compression loss requires full teardown and rebuild, and very possibly replacement rotorhousings and rotors. |