Yes, I had the same exact failure while adjusting the valves. My TT .91FS was running poorly, so I removed the rocker arm covers, and proceeded to adjust the valve. Wow - you really can't torque those locking nut much or the adjustment bolt just breaks. I broke 2! Well after these broke I just dissassembled the entire rocker assembly and the push rods turned out to be bent - both of them. TT (Ace) was kind enough to cover it and mailed me the replacement parts at no charge. I was really careful when I went to torque it back the second time. It seems like really soft metal if you ask me.