I have a Nelson q40 engine that has always stopped at TDC after the fuel line is pinched. This made it real easy to set the prop at 9 and 3 and the prop would be safe on landing. In Florida over the weekend, after about 7 heats, the dang prop started stopping just shy of compression or in the 12 and 6 position. I got lucky on the first 2 landings, but broke a good wood prop the 3rd time.

Where does the prop normally stop, and anyone have any ideas why this engine just suddenly started stopping in the wrong place?

I don't have many good wood props, and I wasn't too happy about wrecking that prop. Any help would be appreciated.

Thanks,