Yamaha Tuning Instability

[Farrell]

My son's piano teacher has a 1983 Yamaha G5 (6' 7") grey market piano. Other than tuning instability, the piano is in VERY good condition. She also has a 1930ish Aeolian 4'some" microgrand in the same room. I have tuned both pianos several times at six month intervals. The Yamaha consistently goes out of tune significantly more quickly than the microgrand. No RH monitoring and no DC (on either piano). The Yamaha does have business card gaps between the pinblock and the flange.

I will be servicing both these pianos two weeks from now. I plan to check the rim screws and pinblock/flange fit on the Yamaha. I will shim any pinblock/flange gaps I can find. She is going to start monitoring RH in the room. But keep in mind, the Yamaha goes much more quickly out of tune than the microgrand. Any other suggestions for things to look for? This is a significant problem for this piano owner. I need to solve it. Any input will be greatly appreciated.

Thanks.

Terry Farrell