Gary.

To get a four cylinder Lyc (or any engine/propeller combination, for that matter) balanced and running as smooth as possible, the engine/prop must be dynamically balanced as a system, while running on the airplane. Many good FBO's have the equipment, usually a Chadwick balancer (or equivalent). It requires attaching a vibration sensor to your engine and a small strip of reflecting tape to one blade of your prop, then running your engine at several different RPM's while the tech eye-balls the prop thru the Chadwick optics to determine where, and how much, weight to add to your spinner back-plate rim.

If for any reason the prop is removed (such as to replace the alternator belt on a Lycoming) be sure it's re-installed in the exact orientation it was in during the balancing or it will likely need to be re-balanced. Re-balancing will also need to be done following a prop overhaul. It also probably would be needed after an engine O/H as well.

In my experience, at least with my local wrench, a Chadwick balance isn't expensive (~$100 or so) and it makes a world of difference in the vibration the airframe and equipment must absorb.

(No affiliation with Chadwick, just a satisfied customer).

Dan Schaefer
LNC2   N235SP --
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