Abstract: A problem existing since 55 years causes Wankel rotary engine to seize before it achieves operational loading conditions. Leading engine manufacturers like Ford, Curtiss Wright, and Bentley have studied this problem and have cited series of patents, but the cause of the problem remains unknown. Existing research literature shows one of the primary indications are the chatter marks, popularly known as ‘the devil’s nail marks’, causing engine failure. The present study focuses on the root cause analysis of the chattering phenomenon occurring at the contact sliding interface between trochoid substrate and apex seal. An analogy drawn from Shobert’s carbon-brush vibration and chatter analysis concludes coefficient of friction, being the driving cause of chatter initiation, is directly proportional to the angle between the contact elements.