Cessna stated read the book that says go by Lycomings figures. ( which I had)
Lycomings figure for the static rated RPM for the Engine was higher than the Cessna figure by quite a large amount and even swopping props with an overhauled one or renewing the RPM gauge I was able to reduce the figure...
The only figures you can use are the type certificate data figures. These are what must be determined when performing an inspection. Lycoming may have engine limits, but this says nothing about propeller limits, and propeller limits say nothing about engine-propeller limitations.
These are spelled out in the type certificate data sheets for the airplane. That Lycoming states the engine may be run to a particular RPM is meaningless. The only figure that has meaning is the one established for the engine-propeller combination, specifically the one found in the TCDS.
Amother reason is that a prop can "untwist" if its not the tacho this happens over a time so its not working so hard and the revs rise slightly....... Overhauling the prop you can have it set to be a climb prop or a cruise prop... If they can, ask them to swop tachos with another one if they have 2 or more aircraft, see it it makes any difference.
"Untwisting" fixed pitch propellers?
There's little point swapping tachometers if you can't verify the calibration of the replacement tachometer.
The answer here is to verify the actual propeller RPM, first. If you don't know the actual propeller RPM, then you don't know anything, and no matter what you do from then on, it's purely guesswork with no baseline for comparison.