<html> Terry, There are always so many factors involved with tuning instability, it's really hard to solve something like this.  In addition to what others have written, keep in mind the following generalizations, which might be contributing factors: - A smaller soundboard tends to react less to humidity changes than a larger one. - An old soundboard tends to react less to humidity changes than a new one. The pinblock gap at the plate flange is not likely to be the issue, as Yamaha grand pinblocks in the past were not fit to the flange.  Some pianos would go together with some contact, but many  did not contact the flange at all.  Same is true for Kawai, by the way.    I believe Yamaha later changed to doing a resin fit, but I am not sure what they are doing now.  In any case, these pianos usually hold tuning just fine without having the pinblock fit to the flange. If you are going to wedge the gap, I would recommend lowering tension and tightening the plate screws first. Have you not already tightened the plate screws?  If not, it might be good to simply do that and see how the piano holds before taking more elaborate steps. Don Mannino RPT At 06:26 PM 9/22/2002 -0400, you wrote: <blockquote type=cite class=cite cite>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   _______________________________________________ pianotech list info: <a href="https://www.moypiano.com/resources/#archives" eudora="autourl">https://www.moypiano.com/resources/#archives</a> </blockquote></html>