(Posted as user eskinner at Rimfire Central.)
I replaced my extractor a couple of months ago (because it just wasn’t there anymore) using parts from Brownells (extractor spring, plunger and extractor). [S&W was “out of stock” on the extractor.]
Look at the ends of the pin holding the firing pin assembly. One side is crowned and the other is cupped. To drive out the pin, push from the cupped end — a firm tap should start it moving. Also, the parts diagram similarly suggests the correct side to which the pin will move during removal.
The “tricks” are in re-assembly. (There’s the “pin” that holds the block in place, and also the “firing pin” in the following description so don’t let the word “pin” confuse you. I’ll always say “firing pin” when I mean that one whereas “pin” means the one that holds the block in place.)
First, rehearse the operations and possible “comes flying apart” possibilities. Some may prefer to do some parts of this inside a large clear plastic bag so that parts can’t fly too far. (I’m thinking of the extractor parts here. I did this without a baggie but, had it gone “sproing”, I might well have had to order more parts because of all the nooks and crannies where flying parts might land.)
Note that one side of the firing pin is flat and must align with the pin’s hole for the temporary (or final) pin to be inserted. When in position, the firing pin will have a small amount of pressure on it from the firing pin spring, and must be held in that position while putting the block back into the gun.
To simplify the “hold it in place while the block is put back into place” process, cut a wire nail or fat toothpick to a length that is slightly less than the width of the block. On the bench, reassemble the firing pin and insert the temporary pin to hold it together. The temporary pin will hold the firing pin in place and in the correct orientation in the block while you set the entire block into place. Then insert the real pin and, in so doing, drive out the temporary pin.
Check operation by manually pushing the firing pin “tail” from the hammer end and making sure it moves freely.