Originally Posted by
Ian Burgess-Barber
Pilots unfamiliar with the engine often operated the engine at the low RPM settings (2300-2700) appropriate to direct-drive engines, while the 175's Operating Handbook called for cruising at 2900 RPM. The low RPM caused harmonic vibration in the reduction gear between the
quill shaft (that turned the propeller) and crankshaft, and the low power resulted in low airspeeds that prevented the engine's air-cooling system from operating effectively, resulting in chronic reliability problems for engines not operated at the recommended power settings.
This article would appear to bear that out:
"Unfortunately, pilots tried to operate the engine along the same guidelines as the non-geared O-300 in the C-172. How, or why, did they do that? I know that I am going to get some 172 pilots upset with me, but many of them shouldn’t be allowed to drive a car in Fargo, North Dakota, on a very slow day."
Geared Continental GO-300 175 hp Six-cylinder Engines