I have a 657 no dash with a 3” barrel that I picked up a not too long ago that I finally opened up for a proper cleaning. When I got the side plate open my suspicions that bubba had been there before me grew. I looked like someone had just slapped a handful of red grease in the frame then squeezed the excess out with the side plate.


The primary issue I’m having is with releasing the cylinder. When I push the thumb piece forward it takes way too much pressure to get the cylinder to open, especially compared to my other N Frames. This has been a problem since I picked it up and was hoping that the cylinder just wasn’t tightened down all the way. But once everything has been cleaned and put back together it persisted. I then took a slight amount of material off of the thumb piece to make sure the bolt could go fully forward in the frame. This seemed to help slightly but there is still considerable resistance to overcome when opening the cylinder. I then compared the locking bolt on the front of the ejector shroud to my other N-Frame’s and there is a big difference to the profile of the part of the locking bolt that connects with the end of the ejector rod.

Does this sound familiar to anything anyone else has experienced or is there something here I’m overlooking? My initial thought would be that the locking bolt might need to be re-profiled but admittedly this problem is over my head.

The other issue I have it when I went to tighten down the strain screw it “bottomed out” and was still protruding from the front of the frame way more than any strain screw on any of my other revolvers. After checking it seems like this strain screw was never fitted to this gun and it putting too much pressure on the mainspring. I backed it out and the trigger seems like it feels about right but the screw head is out to the point where it barely clears the grips when I install them. Is there a standard length for the strain screw on n frames or at least a ballpark value that I could grind it down to or is it a piece by piece kind of thing?

If anyone has any tips or resources for me to reference that would be great of if the best advice is to stay in my own lane and get an actual gunsmith to correct things please let me know. I’d appreciate any input. Also I’ll put up a couple pictures of what I’m talking about so hopefully it is something someone has the answer to.

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I would check out the plunger under the barrel. Sometimes they get crud in the small space they function in. Flood it with cleaner until the junk comes out and it moves back and forth freely. The mainspring strain screw looks long enough that it could be shortened. Does it go all the way in when not pushing the mainspring?
SWCA 892

A couple of other things to check and eliminate as possible causes: check for excessive end shake on the cylinder. As end shake develops, the cylinder moves forward, affecting the extractor rod's interaction with the front locking bolt. (sticking or hang up when opening the cyl)

Another possible cause would be the actual fitting of the center pin. If the center pin isn't long enough, it doesn't retract the front locking bolt past the end of the extractor rod when the thumbpiece is pushed forward.

You can verify proper fitting of the center pin by removing the cylinder from the yoke and placing it extractor side down on a flat, hard surface. Then, while pushing the cylinder down fully on the bench block or table, observe the area at the end of the extractor, and confirm that the the end of the center pin comes fully to the end of the extractor rod, or just a bit beyond the end of the extractor rod. This will indicate that the center pin is properly fit. (check the end of the extractor rod for burrs while you're here)

Excessive runout on the extractor rod can also cause rough opening, as the end of the extractor rod is out of position when the thumbpiece is pushed forward.

Proper enter pin position when the thumbpiece is fully forward:





Carter

__________________
Ret. LE, FA Instr, S&W Armorer

That main spring strain screw is for the square butt models. There is a different screw for round butt frames that is shorter and a different head shape.

__________________
Richard Gillespie
FBINA 102

Beside what's mentioned above, take a look at the breech face/recoil shield. Is the end of the bolt at least even with the surface when the thumb piece is pushed all the way forward. If not, some filing on the face of the leg below the nose is in order.

You might also look at the locking bolt. There's supposed to be a flat on the end to help bridge the gap between the center pin and the ejector/extractor rod. Look very carefully at the end of the rod in the picture in post #3. A locking bolt thats too pointy can catch in that gap.

Good call on the strain screw. I found some online and can see the difference from photos. I’ll be ordering a new one.

I was just able to check this and it looks like my center pin does sit slightly below the extractor rod, enough to catch a fingernail so probably enough to catch the bolt stop as well. I’m going to take the cylinder apart and reassemble again to see if I can tighten it down a little more but if that doesn’t work what is the fix for this? New center pin?

A couple of ways to deal with this. You can simply dress down the end of the extractor rod, or you can take a bit of material off of the extractor rod collar. (make the collar shorter)

The extractor rod collar is inside the cylinder assembly, and can be dressed down if needed to shorten the OAL of the assembled extractor rod, without removing material from the end of the rod itself. Shortening the extractor rod collar doesn't affect any of the other gauges in the assembly, only the OAL in terms of the extractor rod end.

Since your correction is small, it would be simpler to just carefully dress down the end of the extractor rod until the end of the center pin position is correct after assembly. A little polishing of the end of the ex. rod with crocus cloth or very fine wet/dry paper after filing will also help.

BTW, As indicated on the drawing below, Smith and Wesson used to make three different lengths of the extractor rod collar, to accommodate different barrel lengths, and the inevitable adjustments necessary. .190" is the only collar length still available.






Carter

__________________
Ret. LE, FA Instr, S&W Armorer

IT'S A LOT EASIER TO FILE THE END OF THE EXTRACTOR ROD!

Make sure the muzzle end of the centering pin isn't slightly mushroomed and sticking inside of the extractor rod. I had this problem with a pre-owned Model 29-2 that was shooting a lot of full mag stuff before I got it. A discussion on this forum helped me correct the damage and this greatly reduced the needed thumbpiece pressure.