These notes apply to all S&W revolvers. Only minor differences:
Find a perfect fitting screwdriver.
Remove the grip.
Unscrew all the screws on the side plate, don't mix them up.
Roll gun over, push the thumb latch in and open the cylinder.
Slide yoke and cylinder off the frame, go easy not to scratch it.
Roll gun back and find a plastic hammer and tap the frame (near where the grips would be) and the side plate will come loose.
Remove slide plate.
Lift out the hammer block (sheet metal part with a hole on one end, hook on the other CENTENIAL MODELS OMIT).
Loosen strain screw and remove main spring. (J frame insert cotter pin into hole, remove from stirrup).
Pull thumb piece to rear. Press trigger to cock hammer, lift hammer up and off the stud.
Find a screwdriver, and pry the rebound slide off the stud, rebound spring and stem will fly out so keep a finger over opening.
Pull back the hand to clear window, then wiggle trigger off the stud.
You can remove the cylinder stop and bolt but the gains are not worth the trouble.
But if you must, then flip gun over and unscrew thumb piece.
Flip gun back, pull bolt to rear and lift out of frame, watch out for plunger and tiny spring.
Pry out spring for cylinder stop, let the stop drop down and remove stop.
Reverse the operation to put it back together. Find a special rebound slide tool to put the rebound spring back on. It looks like this:
Remember all the guns from J frame to X are nearly all the same internally.
The hammer block sits all the way up before the slide plate goes back on. One end sits on the stud of the rebound slide, the other end sits in front of the hammer. Picture of 500:
Here is a picture of a 686 without the hammer block: