[jclark003]

Over-propping means the engines are being asked to produce more HP than they should at any given RPM. Another way of looking at it is the governor is pushing more fuel than it should to achieve the desired engine speed. High exhaust temperature tends to stress the valve train and shorten engine life. In extreme cases valves can drop resulting in catastrophic engine failure. 

A lot of things can cause an engine to not achieve rated speed including fouled bottom and or running gear (as stated above) dirty air cleaner or restricted air into engine room, fuel restriction (filters, air leaks), props, etc. 

Check with Tiara to see what props were installed out of the factory. It may be the previous owner swapped them without having the prop shop dial them in. If you haven’t done so confirm rated RPM and HP via data plate on the engine. 

Hopefully you and or your engine guy can chase it down quickly.  As previous posts have indicated, ideal setup is to achieve Rated RPM + 2-3% with full fuel and load.