S&W yoke bearing problem

[RJ357]

I bought a used model 66 (no dash). The cylinder had a slight drag at one position in it's rotation. After disassembling, I found a high spot on the front bearing surface of the yoke. The inside of the cylinder must have also had a slight high spot inside, although I couldn't seem to measure it. I left the cylinder alone and took down the high spot on the yoke by about 1 or 2 thousanths and polished everything. That fixed it.
Gun was in nice condition otherwise. Shot just fine.

Anyway, some questions:

1) The bearing surfaces were very uneven and rough. Is that common for S&W's?

2) There were 4 slots cut into the front bearing surface of the yoke. These were at right angles to the bearing axis and were in pairs at two locations. Does this have any purpose?

3) Would it be a good idea to replace the yoke? I think the cylinder is probably not making full contact with the front yoke bearing.

 

[Jim K]

I think you are referring to the part of the yoke called the arbor, the part that houses the extractor rod and on which the cylinder turns.

That arbor has two high bearing surfaces, at the front and the back. They are usually smooth; what is in between is often rough because it doesn't matter. (With that said, I will have to say that S&W quality control has had its ups and downs in the last 30 or so years, and yes, there can be some roughness.)

But note that the cylinder of an S&W revolver does not bear on the small ring in the front of the arbor but on the rear of the hole in the cylinder contacting the back of the arbor. It is there that back and forth cylinder movement (end shake), barrel cylinder gap, and headspace are controlled. The ring at the front, by being in close contact with the gas ring in the cylinder, serves keep crud out of the cylinder hole.

The slots were cut to allow crud from burned powder somewhere to go. They need to be cleaned when cleaning the revolver.

I would not replace the yoke unless there is a serious problem. End shake can be corrected by shims, and as noted above, the cylinder gas ring should contact, but not bear on, the front ring of the arbor.

The Model 66 is a good one, and if the gun is working OK otherwise, shoot and enjoy.

Jim

 

[RJ357]

OK, thanks! The slots were baffling.

What I was mainly worried about was the front of the arbor. The diameter measured from the left to right side was a few thousanths larger than the diameter measured from top to bottom. The front of the cylinder had a little more vertical movement on the yoke. Side to side was OK, since I more or less fitted it in that direction in taking down the high spot.

Actually, the central, non bearing part of the arbor was in better condition than the ends. But it polished up pretty nice, just not perfectly round.

 

[Jim K]

Yes, I think you might want to send that gun back to S&W and let them look at it. Call them up and explain the situation. With luck, they will send you a return label so they pay the shipping. The gun is out of warranty, but S&W has (again) become very good at fixing their stuff with minimal or no charge.

Jim

 

[bountyhunter]

If you are referring to what I call the "yoke tube" which is the tube that goes inside the cylinder when you slip it onto the yoke?

1) You are correct that the very end (rear as installed on gun) of that tube is a bearing surface against the inside of the cylinder. It is this critical fit that sets cylinder end shake. That is the place end shake washers are used to remove end hsake which accumulates from rotational wear there. On old guns, you will see a groove cut into the inside surface of the cylinder by the tube.

2) My new 66 had the same as yours:

"There were 4 slots cut into the front bearing surface of the yoke."

On the edge of the yoke tube. That looked to me like a "swaging press" was used to "stretch" the length of the tube by forcing down part of the end, so the other parts raise up a bit. The end looked like a checkerboard pattern to me. Short yoke tubes are stretched to fit when necessary, but swaging the end is new. They used to peen the end to make it stretch out.

Point is, as you noticed, the tube end was rough and it tore into the cylinder face and loosened up the end shake in about 500 rounds. I fitted an end shake washer to remove the end shake and smoothed the tube end a bit. The washers are made of much harder steel, so the rough end of the tube doesn't wear the washer as much as the inside face of the cylinder.

 

[RJ357]

OK. I'm going to see if I can find out what they would charge.

The very end of the tube (arbor) looked OK, though.