After about 50 flights running a 14x6 @ app: 9600 RPM on ground .The thing sounded worse than usual & then stopped with a helluva bang - prop flew 100 ft ! TheEx rocker arm adjuster broke at the junction of the arm & the jamb nut. The broken off nut jammed between the arm & cover. --Bent push rod ,bent valve . Repair made all O.k .About 10 more runs ,then no power. This time the inlet adjuster broke in the same manner,fortunately it made no contact with the cover . Questions . Has anyone else had this failure ? Why the failure on top of the arm ? Any fix ? My O. 91's have all run well for many years. I don't think I'm overtightening anything .,my internal torque wrench was trained for about 45 years and still works well . Thanking you in advance.ou