Thanks for that report Tim. Probably through dumb luck I've never done it, and have had no real feel for whether the flap valves would manage to close despite the large gap. From what you say, it sounds as if (with that fairly large engine, and correspondingly large crankcase pressure pulses) they managed to close at cranking speed, but the faster the engine ran, the less time they had to close across the large gap.
The easiest way to go is to follow the manual blindly until you've done the job so many times that you do it correctly by sheer habit.
