How to remove a broken rocker cover bolt from the head of a Yamaha Road Star 1700 without disrupting the original threads. A broken off bolt in the head of this Yamaha motorcycle was just not going to come out at all. So we removed the head and with a vertical mill managed to precisely drill out and restore the original threads. If you've ever wondered how to get back to the original threads without having to insert a helicoil afterwards, this is a good tutorial or how too video. Breaking small bolts in engine components is not fun, but you can make the repairs and here we show how.