Lost motion refers to the amount of movement that is not transferred between different parts of the piano action when it is engaged. It is usually because a small gap is present between different components. Because the energy is not transferred, it is referred to as ‘lost’.
Function:
This space is designed between mechanisms to allow a tolerance for action parts to not interfere with eachother. By having this small gap, the parts will always return back to their original place at rest position. For example, with a little lost motion when an upright piano key is released after being pressed, the jack will return under the hammer butt correctly. When there is none or negative lost motion (too much in the other direction), the jack may not return properly and cause the note to misfire next time. This is bad regulation.
Lost motion in most piano actions is usually measured by very lightly tapping the key so it moves slightly down. This should cause some action parts to move and not others in other words, the ‘lost’ motion.
Though it is usually wanted, lost-motion may or may not be needed depending on the type of instrument and the part where it is/isn’t taking place. As such, it is an important part of the regulation procedure in both acoustic and electric pianos along with keyboard regulation, let-off, and damper adjustment.
The electric piano instruments that have lost motion in their design are Rhodes and Wurlitzers, but it occurs in different places:
Rhodes:
For Rhodes piano actions, as the key pedestal directly engages with the hammer cam, there is no lost motion in the lower action. However, the damper arms that are pressed against the tines via damper felt can be adjusted so that they lift a little after the key is depressed. This is a form of lost motion, and is put in place so the damper always fully dampens the tine when a note is not being played.
A minimum amount of lost motion should be approximately 1/8” or 3mm. This is adjusted by slightly bending a damper arm at its centre point. More lost motion can be added than this if desired; and the effect will be to make a note feel slightly lighter. Too much lost motion however and the note will feel sluggish, and the damper may not lift away from the tin at all.
Wurlitzer:
Wurlitzer pianos have lost motion in a handful of places. The first and most notable is the capstan that adjusts when the key engages with the whip assembly. According to the Wurlitzer manual, there should be a slight wiggle in the key up and down of 1/32” or just under 1mm. This is to allow the jack to return to its rest position under the fly, ready for the hammer to strike the reed again. This can also make the touch of the Wurlitzer feel somewhat lighter.
However, because of the low density wood of Wurlitzer keys, and the lack of weights in the keys like grand pianos; adjusting the lost motion to ‘correct’ specifications can lead to an irregular and uneven key height. This presents itself by the rest position of the key varying between different times it is played. Adding mass to the back of the keys can help, but this increases the weight which makes the touch heavier. In later Wurlitzer manuals, no lost motion is suggested here.
For correct regulation here, we would recommend a small amount of lost motion so they key moves a very small amount. If key height is being affected then back it off. This adjustment is made using a thin capstan wrench that is turned clockwise to decrease lost motion, and counter clockwise to increase it.
The other place lost motion is present is the damper regulating screw. This is the hex screw found at the top and back of the action. The damper screw is pulled down by the whip assembly, before pulling down on the damper grommet which in turn raises the damper of a note.
Similarly to a piano or a Rhodes, the lost motion here is designed to prevent dampers lifting when at rest position. Roughly 1mm or 1/32” of lost motion is recommended between. More can be added if dampers are sustaining or to make the touch a little lighter. Here the adjustment is the opposite, clockwise decreases the lost motion and anti-clockwise distresses or.
Sustain pedal:
For both the Rhodes and Wurlitzer pianos, and upright and grand acoustic pianos; the sustain pedal is an important mechanism that requires lost motion. A gap between the pedal mechanism and the damper lift rail allows us to be certain that the sustain pedal is not interfering with the proper position of the dampers. If there is no lost motion, then some dampers may be lifted off the string, tine, or reed; causing an unwanted sustain of the note to happen.
There is no exact amount for how much lost motion to put into the sustain pedal, but 3-5mm of clearance is usually enough to allow the pedal rod to clear the damper rail when released.
For Rhodes pianos, this is adjusted by adjusting the nut on the pedal rod. Be aware that the Rhodes pedal in Mark I and II pianos is a notoriously unreliable design and the slightest movement of the pedal can affect the lost motion and therefore the dampers. Best advice, on a gig or session – tape the pedal down.
For Wurlitzer pianos, turning the knurled nut in the housing assembly underneath the keybed can be undertaken. This can be adjusted to find the ‘sweet spot’. Sometimes if loosened too much the pedal won’t lift the dampers. The opposite is true. If the pedal isn’t working. See our post on this.
