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The main factor that leads to the loss of propeller bolt torque is the variation of the wood hub thickness. The hub thickness will vary with (a) wood moisture content changes and (b) temperature changes. Even though your propeller has been sealed and painted, changes in wood moisture content will occur which can significantly change the thickness of the hub. A one percent (1%) change in the moisture content of a propeller (increase / decrease) will cause a 0.010” change in hub thickness. As the required compression for a typical 65 HP wood propeller is 0.021”, almost half of the required hub compression has now been lost. Moisture content changes are not immediate and can span several weeks or months, depending on many factors such as temperature, humidity, and operating schedules.
Operating temperature changes have similar effects but are not as severe.