Excessive cylinder to yoke movement (not exactly endsahke, but...)

[DocSkinner]

SO first, I know true end shake (cylinder movement while locked) is a key to accuracy. And that is not what I am talking about. this has no end shake when locked.

And know that GENERALLY a little cylinder movement on the yoke with the yoke open is not a problem.

but - when the cylinder hits the forcing when closing unless it is held rearward, that becomes a problem!

There seems to be shims for everywhere else on a SW revolvers except there!

Now may be to long of forcing cone (another issue - CG is only ~0.002 snug or a slip all way around, .003 will not fit any positions), so that is too tight, but not sure getting that opened up to minimum of .003 or up to .006 max will clear enough as when closed and locked there is a 0.016" gap between cylinder and yoke bosses. See attached drawing (yes, crude, I know)


Forcing scone stands proud 0.125".

so opening CG to .006" would give .004" more clearance, but cylinder can still move 0.016. So counting CG, its ~.014 of a problem now, and with .006" CG fix on forcing cone, would still leave ~0.010 interference.



Yoke fit seems perfect. closed there is no discernible edge transitioning from the yoke to frame or vice versa

Is it normal to have that much forward/back play with cylinder open?

are there specs for how tall the cylinder (0.091") and yoke (0.0565") bosses should be so I can see if someone tried a hack gunsmithing job on it?

Best fix if not a cylinder/yoke bearing/shim?


Specs:
Bought used 3" 657. product code 103951 (Special order 6203) so it was an original 3"

 

[Hondo44]

Yes, you clearly have an excessive cyl to yoke gap. Shims come in all sizes or the ctr hole can be opened up to fit the yoke shaft where the issue is shown in your drawing (perfectly sufficient by the way to illustrate the problem).

Or you can replace the the cyl gas ring and do it right. The new part will be slightly oversize so just install it and file it down to size keeping the end square.

 

[WR Moore]

OP, you mention that there is no end shake when the cylinder "is locked". Do you mean that there is no forward and backward motion of the cylinder when the yoke is closed and the hammer is at rest?

OK, the gas ring at the front of the cylinder does not locate the cylinder on the yoke. (Didn't know there was actually a spec for the fit to the yoke. Thanks Hondo44.) The cylinder is located by the rear face of the yoke barrel and the inside rear face of the yoke barrel bore in the cylinder. Usually, one disassembles the cylinder and inserts shims in the cylinder bore to eliminate end play. A properly fitted revolver I've got at hand will allow the cylinder to move backwards on the yoke somewhat when the cylinder is open (the recoil shield/breech face doesn't limit motion), but not forward. It will not contact the barrel shank.

I have to wonder if there might be some excessive play in the fit of the yoke shank to the locating screw. With the cylinder open, can the yoke itself move forward/backward? I've only seen a couple of cases where this has been an issue. Speaking of the yoke, has the yoke/frame alignment been checked with a gauge? If not, it's a good idea.

The barrel/cylinder gap appears to be too tight. Before doing anything about that, first, you should make sure headspace/cylinder to recoil shield measurement is correct (0.060-0.068 in)-usually is- and endplay is acceptable. Then, check barrel/cylinder gap on all chambers to make sure the front face of the cylinder is square. The only .41 I ever worked on had to go back the the factory to get it's cylinder face reworked it varied considerably.

Rather than experiment, why don't you give S&W customer service a call and see what they can do for you?

 

[Hondo44]

The cylinder is located by the rear face of the yoke barrel and the inside rear face of the yoke barrel bore in the cylinder. Usually, one disassembles the cylinder and inserts shims in the cylinder bore to eliminate end play. A properly fitted revolver I've got at hand will allow the cylinder to move backwards on the yoke somewhat when the cylinder is open (the recoil shield/breech face doesn't limit motion), but not forward. It will not contact the barrel shank.

I have to wonder if there might be some excessive play in the fit of the yoke shank to the locating screw. With the cylinder open, can the yoke itself move forward/backward? I've only seen a couple of cases where this has been an issue. Speaking of the yoke, has the yoke/frame alignment been checked with a gauge? If not, it's a good idea.

Rather than experiment, why don't you give S&W customer service a call and see what they can do for you?

WR Moore is correct. A simple shim in the cyl ctr hole will take up cyl fore and aft play by extending the yoke axis shaft. However on a worn revolver as I presume yours must be, too much shimming will move the cyl too far back, open the cyl gap too far and even cause closing the cyl and/or headspace problems because it will be too tight at the rear and contact the breechface.

I'm surprised to see so much play in a modern revolver. His idea of calling S&W might be the best in this case.

 

[DocSkinner]

WR Moore is correct. A simple shim in the cyl ctr hole will take up cyl fore and aft play by extending the yoke axis shaft. However on a worn revolver as I presume yours must be, too much shimming will move the cyl too far back, open the cyl gap too far and even cause closing the cyl and/or headspace problems because it will be too tight at the rear and contact the breechface.

I'm surprised to see so much play in a modern revolver. His idea of calling S&W might be the best in this case.

Thanks both -
Wasn't planning on fiddling myself other than maybe bushings, if that was all it needed, but was more trying to figure out exactly what all would need done and whether just back to S&W for a lot of work or if more minor find a good localish smith if just the CG needed opened.

I have a 57 to compare with, but not sure how much difference there is between the blued and stainless, and different generations as well.

Your questions:



With cylinder open, yes, the cylinder will move forward and back, it will close that gap depicted in the picture. But no, there is movement of the yoke relative to the barrel.

Ratchet area is definitely in full contact breech face and that is rearward limiting factor.

Cylinder closed, not cocked, it has a tiny bit of fore/aft wiggle.

Cylinder closed hammer cocked, barely any fore/aft movement.


And so rather confirmed my thoughts/fears of it probably needing to just go back for a factory overhaul.

Wonder if someone in past tried to fit a new cylinder and did a terrible job?

Thanks for confirming it needs to go back. Now I don't feel like I am just worrying about it too much. Good mechanic, but far more of a gun shooter than a gun smith!

 

[armorer951]

If you have fore and aft movement of the yoke with the cylinder closed you have what's called "end shake yoke". This can be due to wear and tear on the yoke button, or someone substituting the wrong piloted sideplate screw for the one that is supposed to be on the yoke. (perhaps someone switched the screws) Prior to yoke revision/redesign, the yoke (the yoke button) was individually fit to the yoke screw.

Repair strategies include fitting the yoke button to a new yoke screw, switching the two piloted screws in the sideplate, or peening the yoke button back slightly at the fully closed location on the button. You want the yoke to open and close freely while it is in contact with the pilot on the yoke screw.....but, there shouldn't be any "gauge" or fore/aft movement at the screw pilot/yoke button interface (point of contact) during the opening and closing of the cylinder.

I'm curious about the rear gauge or headspace measurement also....space between the rear of the cylinder and the breechface, w/cylinder closed.

Carter

 

[DocSkinner]

If you have for and aft movement of the yoke with the cylinder closed you have what's called "end shake yoke". This can be due to wear and tear on the yoke button, or someone substituting the wrong piloted sideplate screw for the one that is supposed to be on the yoke. (perhaps someone switched the screws) Prior to yoke revision/redesign, the yoke (the yoke button) was individually fit to the yoke screw.

Repair strategies include fitting the yoke button to a new yoke screw, switching the two piloted screws in the sideplate, or peening the yoke button back slightly at the fully closed location on the button. You want the yoke to open and close freely while it is in contact with the pilot on the yoke screw.....but, there shouldn't be any "gauge" or for/aft movement at the screw pilot/yoke button interface (point of contact) during the opening and closing of the cylinder.

I'm curious about the rear gauge or headspace measurement also....space between the rear of the cylinder and the breechface, w/cylinder closed.

Carter

There is no movement of the yoke. (well other than the opening closing like it is supposed to!)

And the 0.016 gap area is larger with cylinder open, the recoil shield/breech face forces the cylinder forward when closing.

getting far deeper into the parts of a cylinder than I have in 40 years of owning SW revolvers!


Correct me if I am wrong on these points below:

The cylinder assembly free floats on the yoke, correct? so the cylinder is restricted in rearward motion by the small boss on the lower left rear corner of the frame window when open, and then by the bearing surface in center of ratchet when closed? The gap between the rear face of the cylinder and the frame is consistent 0.064" top and bottom.

The ratchet teeth and center boss are uniform in height - 0.095" (shouldn't teeth be slightly shorter so that only the central bearing/boss of the ratchet actually bears against frame?)

forward motion of the cylinder is normally restricted by the rear end of yoke barrel interface with the inside face of yoke bore in the cylinder. Where you would normally place shims/bearings to correct end shake.

SO closed, the cylinder fore/aft motion is normally restrained/determined by the bearing in center of ratchet against frame and internal bearing surfaces of the end of the yoke barrel and the internal vertical face of the cylinder center bore?

Are there set specs/limits on how far the forcing cone protrudes from the frame (0.125") or cylinder length (1.672")?

 

[WR Moore]

getting far deeper into the parts of a cylinder than I have in 40 years of owning SW revolvers!


Correct me if I am wrong on these points below:

The cylinder assembly free floats on the yoke, correct? so the cylinder is restricted in rearward motion by the small boss on the lower left rear corner of the frame window when open, and then by the bearing surface in center of ratchet when closed? The gap between the rear face of the cylinder and the frame is consistent 0.064" top and bottom.

The ratchet teeth and center boss are uniform in height - 0.095" (shouldn't teeth be slightly shorter so that only the central bearing/boss of the ratchet actually bears against frame?)

Headspace/gauge is ideal, right smack in the middle of the range. The guys who build PPC guns usually reduce the height of the ratchet teeth by 0.005 in, but that adds a machining operation and can complicate fitting.

forward motion of the cylinder is normally restricted by the rear end of yoke barrel interface with the inside face of yoke bore in the cylinder. Where you would normally place shims/bearings to correct end shake.

SO closed, the cylinder fore/aft motion is normally restrained/determined by the bearing in center of ratchet against frame and internal bearing surfaces of the end of the yoke barrel and the internal vertical face of the cylinder center bore?

True, but the forward motion of the yoke is also limited by a lug just ahead of the start of the yoke barrel. It's a small projection, you might overlook it.

Not sure if the barrel shank is individually fitted or if the barrels are machined to a specification and simply installed. I once had a barrel replaced under warranty (horribly canted end of the forcing cone) and asked if they'd leave it raw and I'd fit the B/C gap. They did, I did.

Simple tolerance stack is going to produce some variation in length of the barrel shank protruding into the frame window. There is a spec for cylinder length, but again, there are production tolerances.

The general rule of thumb for tolerances is that if you're making a hole, it can be oversize from nominal, but not under size. If you're making something that goes into a hole, it can be under size from nominal, but not over size.

 

[DocSkinner]

Simple tolerance stack is going to produce some variation in length of the barrel shank protruding into the frame window. There is a spec for cylinder length, but again, there are production tolerances.

The general rule of thumb for tolerances is that if you're making a hole, it can be oversize from nominal, but not under size. If you're making something that goes into a hole, it can be under size from nominal, but not over size.

Yes, and production tolerances are exactly what I was asking for! as a licensed aircraft mechanic, we didn't just use "Hole has to be bigger, bolt has to be smaller" but instead use specifications. Everything had a nominal value and a plus and/or minus tolerance value.

So I am used to production specifications INCLUDING tolerances unless that is totally different with guns (which I doubt) so all these parts should have nominal values with a plus and minus tolerance listed somewhere. But no one seems to have that data available outside the factory?

 

[Hondo44]

Where have you looked? Don't expect that info in forum posts except for an occasional spec given. Where are specs for the aircraft industry? There are manuals with this info, correct? If you want that info for S&Ws, don't you want to start with a manual? Click on the bottom line in the below:

[ame]https://www.amazon.com/Revolvers-Shop-Manual-New-Expanded/dp/B00QVPEAE0/ref=sr_1_3?dchild=1&qid=1619023157&refinements=p_27%3AJerry+Kuhnhausen&s=books&sr=1-3[/ame]

 

[WR Moore]

As a machinist I made parts that might have tolerances of +0/-whatever or +whatever/-0. Some times I had a whopping 0.001 in tolerance. That said, the folks installing said parts didn't need to know the production specifications to include tolerances.

And, as Hondo44 notes, if you seek, you will (sometimes) find.

 

[DocSkinner]

As a machinist I made parts that might have tolerances of +0/-whatever or +whatever/-0. Some times I had a whopping 0.001 in tolerance. That said, the folks installing said parts didn't need to know the production specifications to include tolerances.

And, as Hondo44 notes, if you seek, you will (sometimes) find.

Sometimes find is key words.

And when you have to check dimensions, you kinda need, well dimensions. Great that you machine to 0.0001". I measure parts in that range to make sure they are in spec - and they will be spinning at up 38,000 rpm. But we are, I thought, talking about pistols here, not trying to compare who can talk about bigger, uhm, tolerances.

I don't plan on machining a new pistol. I don't need every spec for the pistol.

I thought maybe some friendly person on here that has them might share them so I can look at my pistol and see what I need to tell S&W about getting it repaired. Is it just an accrual of tolerances? Is it a bad cylinder? is it that someone decided to shave a few thousands off the barrel so the forcing cone was closer to get a (too) tight CG? SO is it something that is a warranty item, or is it something someone did after that I get to now pay for?

But, alas, I guess such a simple request is just too exorbitant? I am betting a few people other than me would like similar information that also don;t want to machine a pistol or any parts, but would like to see where they may be getting problems. That, I thought, was why we have these forums - to help provide information to other SW fans/owners to help them.

 

[DocSkinner]

Where have you looked? Don't expect that info in forum posts except for an occasional spec given. Where are specs for the aircraft industry? There are manuals with this info, correct? If you want that info for S&Ws, don't you want to start with a manual? Click on the bottom line in the below:

Amazon.com

Yes, we have shop manuals. Not all of them cover the specs. So this manual I can gamble that it might have these dimensions or like most shop manuals will only have measurements like CG, and then talk about endshake and how much is too much, and how to assemble/dissemble and lubricate and clean. I'll order it, if it doesn't have the measurements, it will be on your dime?

Or do you have it, know that it has the dimensions, but just don't want to share that information?