I read a story on the net many years ago of a test flight carried out at Mascot in an investigation into the unexplained losses where engine fires were a feature. In a steep dive the test pilot found the cause to be prop overspeed and reduction of throttle sucked the tops out of the pistons (underboost), with subsequent fire due oil escaping through the holed piston. He managed to get the aircraft back on the ground at Mascot where it was written off due damage incurred. Have searched over the last few days following Centaurus post, but unable to find. Perhaps someone with better search skills than I can find, believe it to be Beaufort A9-585 and the date 16/07/44. The Beauforts came with either electric or hydromatic props and the trouble turned out to be underweight counterweights on the hydromatics from memory.