For very old pianos.
The walls of the drilled holes in an old piano pinblock can lose their grip on the pin. The interior walls of the hole become too smooth to hold the pin fast. There are other causes too, but the repair is the same.
Remove the pin.
Wear leather gloves.
Loosen the pin using a tuning lever. Go slowly. You will need to remove the wire from the small hole in the pin. The wire is old and brittle. If you turn the pin too much, you will break the end of the wire. If you break it, you just made an easy repair a difficult one.
After you remove the end of the wire from the hole in the pin, slip the coil of wire from the pin. Set it aside.
Continue turning the pin until you can remove it.
Three options now.
Option 1 – (The quick fix). Cut a small sliver of aluminum from an empty soda pop can. Use tin snips. The strip of metal should be the width of 1/4 of the circumference of the pin hole, and not longer than the pin hole.
Option 2 – Use a two-part bonding glue. (Available at Walmart). Mix the two agents onto a piece of paper. Coat the pin and return it to the pinhole. Let the glue set. Use the tuner lever to “break” the bond of the glue. Restring the wire and tighten to pitch.
Option 3 – Replace the old pin with a pin one size larger.
Returning the pin to the piano.
Grand piano – Remove the action. It is VERY IMPORTANT to block the pinblock under the hole of the pin to be replaced. Use pieces of 2 x 4s to create a brace between the underside of the pinblock and the keybed. Use a small jack if you have one. Make sure the pressure of the brace does not put undo upward pressure against the pinblock. The idea here is to redirect the force of a hammer blow (needed to drive the pin back into the hole) to the brace, and then to the keybed. The brace should be snug. Wedge it into place with light taps of a hammer. If you do not do this properly, you can crack the plate. END OF PIANO.
Place the strip of aluminum into the pin hole. With a 4-8 lb hammer, and a pin setting tool, drive the pin back into the hole. Leave the pin a little higher than the surrounding pins. Return the coil of wire, and CAREFULLY reinsert the bent end of the wire into the pin hole. DO NOT BREAK IT. Slowly tighten the wire, lifting the coils of the wire as you tighten the coil is tight. Use a string lifter tool to do this. Check the alignment of the piano wire to make sure it is exactly where it was. When the piano wire begins to tighten, use the hammer again to tap the pin so it is 1/16th of an inch above the height of the other pins. Tighten the wire and retune the string.
For an upright piano, there is no need to block the pinblock.
It is much easier just to pay a technician to do this. That is what I recommend. The tech will have special pinhole inserts that are better than using a piece of aluminum.