<HTML>.           Brian          It seems like the possibilitys for geometry error in this case is could be endless. It sounds to me that you've installed a wippen that is designed to fit a 17 or 18  mm knucle placement and are still using a shorter knuckled shank. I'll bet the jack had to be regulated closer towards the player and the angle of jack to knuckle is at a less than ideal angle. This could be why the jack is slamming into the cushion. There is just not enough room for the jack to travel. With limited info this is my first thought.   What kind of action/brand are we discussing? I believe 4 1/2" is longer than most yamaha and Kawai. I think the correct spread is 112.5mm which is shorter than 4 /12". Try moving the wippen rail forward then adjust the jack farther back and see how this effects clearance, weight and reg.    >>>Dale Erwin>>>>...    <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">Hi list, I've been doing some reading, at least what I could find at my fingertips, on action geometry, and although I can find a lot of general stuff, and a lot of theory, specifics aren't quite as easy. I've changed out the wippens and shanks/flanges/knuckles on a well known action. The new parts are Renner and are the closest I could get to original dimensions.  However, they are NOT identical. The wippens are shorter in length by about 3mm, the variation appearing to be mostly out at the jack end of the wippen. When I leave the action spread at 4 1/2", as was the original, the jack doesn't have room to clear the knuckle before it burys itself in the felt stop at the end of the wippen. </BLOCKQUOTE> </HTML>