Help needed...

[AJR337]

I just finished doing a detailed cleaning and spring replacement on my new to me 640 no dash.

Additionally, I installed shims to eliminate some minor yoke play (front to back) and cylinder endshake. The lockup is now very good and the barrel/cylinder gap is measuring .007/.008 so I'm happy with those results.

After reassembling and visually reviewing/function testing, I noticed that if I apply pressure to the side of the cylinder, the yoke moves slightly away from the frame.

I checked the yoke screw and it was tight so I went ahead and removed the yoke/cylinder, removed the yoke shim, reassembled and it still had lateral play.

Next, I tried a new J frame yoke screw and that seemed a bit better but I still had yoke play/movement.

Finally, I had an extra yoke screw for my 686 so I tried that to see what might happen...while the screw is obviously too long, once iI tightened it, the yoke play/movement was gone.

So with the standard 640 yoke screw, there's yoke play and with the longer 686 there's none but it's too long/the head protrudes from the frame.

And ideas about what's causing this issue and how to address it?

 

[AJR337]

If it helps, here's a picture of the yoke...

And I'm using the newer spring/plunger screw.

 

[steelslaver]

The yoke screw isn't supposed to stop lateral play. It is supposed to limit front to back play. lateral play is a function of the center pin riding in the recoil shield, the cylinder riding on the yoke tube and the barrel lug fitting into the end of the ejector rod. With the gun empty does the yoke move away from the frame when your cocking either via single action or double action? I suspect its something other than the yoke screw. The yokes pivot should fit snugly into the frame. The hole in center of the ratchet should be snug on center pin, center pin should fit snug in recoil shield. Ejector rod should be straight and the barrel lug should enter it about 1/8". Ejector rod should fit its hole in yoke snug. Should be no real lateral play even with the yoke screw out.

With the 686 screw tight does your cylinder open smoothly?

 

[AJR337]

I understand what you're saying but my 686 does have some minor lateral yoke play until I tighten the yoke screw. Once the yoke screw is tight, the yoke play is gone.

I can't remember if I tried to open/close the cylinder with the 686 yoke screw installed.

If that's important to know, I can reinstall it and report back?

 

[WR Moore]

On your pistol, the yoke screw is a fitted part. As noted above, it's to keep the cylinder assembly from falling out of the frame when the cylinder is open.

Just sticking any old screw into that location can cause you problems, specifically with excessive wear on the button on the end of the stud. In fact, it appears there is wear on it in your picture. Possibly the previous owner(s) mixed the screws up?

Sticking that too long screw in forced the yoke stud against the frame. It would probably not allow the cylinder to swing out. As also noted above, lateral movement is regulated by the center pin, breech face, locking bolt and extractor rod and the alignment of yoke to breech face and yoke/cylinder tolerances. NOT by the yoke screw. You might closely inspect how the locking bolt and extractor rod fit together. Poor fitting and/or idiots "improving" the product can cause issues here. I worked on several pistols where people dealt with bent extractor rods by hacking away at the locking bolt.

Might be time to consider a visit to the mother ship or a good revolver mechanic. Another option is to quit applying side pressure to the cylinder.

 

[AJR337]

Thanks for everyone's responses.

The locking bolt should operate with fairly firm spring pressure - correct?

I took another look and noticed the the locking bolt does not appear to be have much spring tension...I can actually lightly tap it and it'll move about a 1/10 of an inch before the spring begins to push back which is a bit strange since I just replaced the spring and cleaned everything out. I did notice that the old spring seemed to be a bit longer... I'm assuming that this could be the issue?

 

[WR Moore]

May or may not be the issue, but it's not right. The amount of spring pressure isn't really firm, but there shouldn't be free travel and the locking bolt is supposed to engage the extractor rod and prevent/limit sideways movement.

Itty bitty parts sometimes get confused in parts bins. I've received K frame parts when I ordered N frame parts. You might try another spring and locking bolt 'cause something isn't right.

 

[AJR337]

I agree... the locking bolt on my 686 is under constant spring tension and provides much more resistance when pushed... I just ordered a new locking bolt and another spring so I'll give that a try and see if it helps.

 

[steelslaver]

Not just a spring in there short rod too. Not all the same

 

[WR Moore]

I'm pretty sure we're talking about the widget out on the barrel (locking bolt), at least I am. Not the bolt inside the frame. I can sort of see the logic to the naming, but it can get confusing.

 

[AJR337]

Yes, I'm referring to the locking bolt and spring...I looked at it again this morning and noticed that the bolt is not making any meaningful contact with the ejector rod so I'm assuming that's the issue. I'll report back once I receive and install the new parts. Thanks again.