It just dawned on me as for this 1926 Steinway A.It actually makes a difference as for whether the piano is a Hamburg A or a New York A. In that you are in Japan,is it a Hamburg A.? ...

Hi Cy
>Another important distance is hammer flange center pin to knuckle.

Does the meaning that you say : from a center pin to the center of the knuckle board?

Cy,The piano is most likely a 1926 AIII of s/n 245... Action stack is the same as an AII. I usually buy Renner USA the modified style(larger knuckle)#913029 shank flange and #913048 angled heel wipps. This is what my rebuilder prefers as for Renner USA parts. Can't complain,they feel great on a AIII. Center pin to the wippen flange on these new parts is 113mm.

hi Pianobroker

>the 9mm knuckle for higher ratio action.
16.5 mm is the distance for the "modified" shank flange which utilizes the 10mm knuckle supposedly for a lower ratio
setup. I personally prefer the larger knuckle feel giving a smoother,lighter lower ratio feel. Personal preference


I understood.
Is level rattling of hammer shank flange corrected by paper or felt?

Yes you can paper a flanche if the center is not well aligned, but you usually have to be careful when screwing the flange for the first time, as this is when the screw makes its circular on the flange, afterthat it will tend to go back there. You can move it screwing the flange in another place while holding the shank with some pressure.

a little lube helps for the screwing.

Old Steinway stacks and keyboard where intended for a very high ratio, around 7.0; far tfrom modern (5.5) so you can end with 11.5 mm key dip with modern parts if you dont take that in account.

Modern parts and heads hardly can be used with those high ratio, adding tons of lead or using assist spring will help but the feel of the action can remain heavy. I believe that original shanks/heads where more than 1.8 g less in the treble for instance (shank -0.4, hammer -1.4g).

This is the basis of the problem with old actions the key leverage is often high (big advantage on the key side) and the stack is accelerating more than actually. When you use modern parts compromises are necessary ,like shimming below the whippen flange to get to a better spread, but then the key need a long keydip so the hammer stroke is 45mm (at last)

Having samples of the parts may help to experiment before changing.

Good luck

Olek


Unfortunately 　I don't have Renner sample partskit．
I'll try again.

17mm is the present Hamburg spec which is also available via Renner USA.
15.5 mm is the distance .....


Disclaimer: nontech opinion