Yamaha out of tune

[Elian Degen]

Hello List and all

My experience with Yamaha, and I have seen lots of them in the last years,
is as the easiest piano to tune and Yamaha tunnings last a long time ( they
have greater stability than many pianos. )

Several month ago I was called to repair a Yamaha, it is an Upright model,
serial  M1JD3467278, not much to do, an action adjustment, some hammer
reshaping, very much out of tune, but I considered it was dur to the long
time without service. I took the pitch up, tuned it to 442, and I convinced
him to have it tuned twice for the next month.

After that he kept calling me and every time I check the piano is out of
tune again, tuning won´t last a month.

I checked tunning pins, they are firm and look excellent condition.
I checked the bridge, hitch pins.
Cheked humidity and temperature

Also pitch stays were it is (442) in general,  when I tune it some strings
seem to be higher others lower, to give you an idea they move about half
beat appart from each other. I haven´t seen anything like it.

The place where the piano is located is cool, stable temperature, there are
no heaters nor air conditioners,

The pianist plays nicely, doesn´t strike the keys.

If anybody has any idea........


Thank you

Elian