The last New Model No. 3 rolled off the production line at Smith & Wesson 113 years ago.  Any weapon that old can and will have mechanical issues.  One cannot just ring up S&W to order replacements.  How then does one solve problems with broken or worn out parts?  You have three possibilities: 1) Obtain a like pistol and scavenge the needed item from that gun.  2) Make the part yourself.  3) Find someone who already has the part or has experience to make a replacement for you.

I think that most would agree that cannibalizing an old pistol would not be a good choice.   You could learn to machine and the heat treatment process.  I feel that for a part directly in the line of mechanical operation for a firearm should be created by someone that has experience.  The leaves option three, find someone who already has the part or will make a replacement for you.

The S&W New Model No. 3 Frontier pictured here and further described on another page, developed a soft and then broken cylinder stop spring.  Replacing this part is what will be discussed here.

First, do NOT make your initial experimentation being a gunsmith using a pistol that some might find valuable.  That would be stupid.  If you are not already very familiar with gunsmithing in general, have someone else who is, perform this work.

Having now given that warning, this particular repair can be relatively simple.  The biggest hurdle to overcome in gun repair is to correctly identify the issue BEFORE you do any repairs.  Sounds simple and you would think that everyone would follow such advice.  Most people don't.  Just like most people do not read provided instruction first.  Don't be "that guy".  One simple slip of the wrong sized screwdriver can forever mar a weapon.  Forever decrease its value.  Heed the warning..............

How do you determine that the cylinder stop spring needs to be replaced?  Or that the problem is even actually the cylinder stop spring?  Nothing is 100%.  These steps should provide you with the best chance of determining the root cause of your issue.

1) The cylinder stop spring affects the timing of the pistol.  Check the pistol timing.  Do this with the pistol UNLOADED.
2) Hold the revolver in your dominant hand to cock the hammer with your thumb.  With your other hand, have those fingers just barely touching the cylinder.  You are looking to have only the slightest pressure against the cylinder during the cocking of the hammer.
3) While slowly pulling the hammer back to full cock, listen.......
4) You should see & feel the cylinder begin to move as you start pulling the hammer back.
5) You should hear a click as you pull the hammer back over the half cock notch.
6) Nearing the full cock position, you should hear a slight click & feel the cylinder stop snap into place into one of the machined cylinder recesses, just before the hammer goes to full cock.
7) You will hear the hammer click into full cock.

The click from the cylinder stop should be heard/felt just an instant before the gun goes into full cock.  You will have to do this many times to be sure that you see, feel, & understand as each of these is happening.  You should be able to feel that the cylinder "locks" into place BEFORE the hammer clicks into full cock.  If you ever plan on firing your revolver, it MUST successfully perform this test.  Otherwise you would shave lead as the bullet travels into the barrel (That hurts!).  At the worst, the cylinder might be way out of alignment with the barrel when the round detonates, causing a catastrophe and injury.

This discussion is about the cylinder stop spring, so what you would see/hear if the cylinder stop or stop spring is the issue would be:

a) While slowly pull the hammer back to full cock,
b) You see & feel the cylinder begin to move as you start pulling the hammer back.
c) You hear a click as you pull the hammer back over the half cock notch.
d) Nearing the full cock position, you DO NOT hear a slight click.  You DO NOT feel the cylinder stop snap into place into one of the machined cylinder recesses.
e) You hear the hammer click into full cock.
f) At this point you may or may not feel the cylinder locked into position.

If the cylinder is not locked into position, DO NOT fire the pistol until issue is resolved!

The problem is likely either the cylinder stop or the cylinder stop spring.  Now to refine the diagnosis further.  Next.

8) Have a qualified gunsmith do the work!  Particularly a gunsmith who has worked on S&W Top Break revolvers before!  If you are qualified & choice to proceed,
9) Open the revolver as if unloading.
10) On the inside of the frame, above the trigger you will see the cylinder stop hole in the frame and one screw. [Image 1]
11) With the exact/correct screwdriver, loosen & remove this screw.
12) Carefully, remove the trigger housing from below with a downward pull.

Remember that this revolver is well over 100 years old.  If it does not come off do not use too much force.  Could be rusted on.  Could be bent.  If you are not adapt at understanding and resolving these types of issue, see #8.

With the trigger guard off you can now do further diagnosis . [Image 2]

13) Check the inside of the trigger guard (the portion that was against the frame).  You will see the cylinder stop spring.  What does it look like?
14) Do NOT be tempted to bend the flat spring.  Bending a spring this old will very likely cause it to break!
15) Is the spring flat against the trigger guard or is it in a bent up positon?

Flat against the guard indicates it is weak and does not apply enough pressure against the cylinder stop to force it into correct position in the cylinder.  Bent up means it may be functioning correctly and the issue is with the cylinder stop itself, not the cylinder stop spring.

16) On the bottom of the guns frame, in front of the trigger you will see the bottom of the cylinder stop.  Push on the bottom of this cylinder stop.   It should move freely up & down, in & out of the slot cut in the frame that allows the part to fit into the cylinder when in place.

If the cylinder stop does not move freely, and without any further disassembly, attempt to clean and oil this area to free up the cylinder stop.  If the cylinder stop was sluggish or did not move freely before, once cleaned reassemble the trigger guard without doing anything to the cylinder stop spring.  Reassemble and repeat steps 1 through 7 several times.  If this solved the issue, you are done.  If not, and you are sure that nothing is preventing the cylinder stop itself from functiong as designed, then..........

17) Carefully attempt to place a blade or other thin flat surface under the end of the cylinder stop spring on the trigger guard. (This is a last resort, as the spring will likely snap, necessitating a new spring).  Attempt to bend up the flat spring.  Do not over do it!

Refit the trigger guard to the frame and repeat steps 1 through 7 several times.  if this solves the problem, great!  It is likely however that this will not work.  You will retry bending the spring and eventually it will break.  A through search on someplace like smith-wessonforum.com/ should produce options for a new cylinder stop spring.  Now onto its replacement.

< With the replacement cylinder stop spring in hand, remove the trigger guard as described earlier.
< Soak the trigger guard & the cylinder stops spring it holds with oil designed to loosen stuck parts.  it is so likely that you will need this, I would not even attempt removal beforehand.
< In a padded vice, secure the trigger guard with the spring showing.
< Using a correct sized punch, strike the old spring using a hammer in a manner to push the spring out of the trigger guard.  Go slow.  Not too much force.
< Once the broken spring is removed, go over the surface where the spring is held in place with something like Emory cloth to smooth & remove any rust or grim.  Clean & oil the area.
< Carefully attempt to refit the replacement spring into the trigger guard.  Do not force as the replacement spring could become damaged.  The spring is dovetailed and only goes in one way.
< If new spring does not fit, use a stone to remove very small amounts of metal from the spring in those spots that are preventing the new spring from fitting onto the trigger guard.
< Snug is good.  Tight is bad.

*Note: The cyllinder stop spring is NOT a flat 90 degrees on the sides.  Instead it has dovetailed sides and can only be removed or installed by being pushed in and out of the slot.

Reinstall the trigger guard containing the replacement spring and again try steps 3 through 7 until the revolver functions as designed.  If after all this you are still unable to resolve the issue.  Take the pistol to a gunsmith.

Below image shows the actual cylinder stop spring: Old broken spring still in place.  New spring in place.  Old and new spring side-by-side.