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Interesting thread... I'm no engine builder but I've heard at least a couple of piston guys mention using increased piston-to-cylinder-wall clearances to avoid contact due to the piston expanding when it sees a lot of heat (high boost). Due to the shape of the piston inside the cylinder I don't think those guys would be need to be very concerned with flex or eccentric shaft wobbling... I would venture it's just expansion from heat.
I suspect there are some similarities and some differences between how the piston engines and a rotary engine will react to the additional heat (not a lot of forged aluminum rotors out there), but something along those lines may account for why some builders are suggesting that increased clearances and others don't. I suspect it may be more important in engines that are seeing a lot of heat. This may explain why one builder observed a higher percentage of FD failures than FCs... it's pretty much a given that the FD runs hotter.
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