Cessna T-210 propeller balance problem

[mcdriver]

T210, just finished annual by trusted mechanic.

Another service on our field offered a discount for propeller balancing. I agreed, even though I have not noticed any vibration, he said it might improve performance and lessen noise level in flight.

He was unable to balance the prop.

He states "Unable to complete propeller balance due to mechanical problem with engine or propeller." No other opinion from him.

I have not had any vibration problems with this plane.

Engine has less than 400 hrs since factory reman.
Prop has about 900 hrs since overhaul.
My mechanic who just finished the annual says he cannot find any reason for the prop to not balance. On test flight no noticeable vibration.

Anyone have an idea what the possible mechanical problems might be?

Thank You

[Big Pistons Forever]

I saw a similar issue with a Cessna 185. There was some vibration but not an unusual amount, but the owner decided to give prop balancing a try. The technician could not balance the prop because he could not get a steady reading on his equipment.

After much research it was decided that there was likely an internal engine issue. It was also found that one prop blade serial number was different from the other blade but there was no record of any prop work in the logs. Finally there was a "rumor" that the airplanes tail had been blown up in a wind storm with the prop vertical causing one blade to hit the ground and be bent when it was operated by the previous owner.

Bottom line: The engine was torn down and a crack in the front main bearing web was found. It was considered likely that the engine would have eventually suffered a catastrophic in flight failure :uhoh:

[ChickenHouse]

- internal engine problem, not steady enough operation
- engine shock mounts worn (were they changed on OH?)
- disbalanced spinner (cracks on the bulkhead plates?)

These are the first three coming in my mind. I had No 2 and 3.