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Broken Yoke!


Carmoney

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33 minutes ago, Toolguy said:

I have a SS one I might part with for a really good friend, but you probably don't want to end up with a Pinto gun.

 

Warren, I love Pintos!  My first car was a Mustang II, which is pretty much the same thing as a Pinto.  

 

I promise I would give that SS yoke a really good home!  

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On 6/28/2022 at 9:15 AM, pskys2 said:

Cause?  Did it start as gas cutting as in top straps on M19's?

 

 

No idea.  I wouldn't think my minor loads would be blasting out a whole lot of gas.  That gun does have a lot of rounds through it, maybe it just got tired.  

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On 6/30/2022 at 5:53 PM, Carmoney said:

I am very gentle.  😉

Just curious, can you tell which direction the fracture started from? Usually with a magnafier you can see where it started to crack as it will be dirty or polished depending on how long ago it started. I always try and figure out why or how in hopes of preventing it from happening again. 

Edited by Farmer
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  • 2 weeks later...
On 7/2/2022 at 12:01 PM, Farmer said:

Just curious, can you tell which direction the fracture started from? Usually with a magnafier you can see where it started to crack as it will be dirty or polished depending on how long ago it started. I always try and figure out why or how in hopes of preventing it from happening again. 

 

I can't tell where the fracture started.  I've messed around with it so much that the broken surfaces all sorta look the same to me.  

 

I suspect it's nothing more than metal fatigue over 15-20 years of heavy use.  I actually am quite gentle with my revolvers--my reloading technique does not involve the wham-slam moves that I see certain other shooters do.  Even at full speed, I open them gently, and I close them gently.  

 

I suppose it could have been caused by hot gases gradually cutting down from the cylinder gap, maybe?  This gun has never seen more than a few magnum loads, but I have shot a whole bunch of competition ammo (typically about 140 p.f.) through the thing.  I have dealt with a lot of revolvers over the years, and I don't believe I have ever seen this particular failure happen on any of them.  I'm going to chalk it up as a fluke event, I guess.  

 

One thing I have learned from this--there is a reason S&W insists on installing these at the factory.  There is nothing much involved in the actual "fitting" process, and they pretty much drop right in--but they apparently have made a ton of variations of yokes!  The stainless one that Toolguy sent me had a yoke barrel that was about .2" too short--not sure what kind of gun it came from--maybe a 625?  The blue yoke that MRBerg gave me was designed slightly differently (it came from a damaged 29 Classic), and initially it didn't work either.  But earlier this evening a machinist friend and I were able to fix it by fabricating a .06" stainless spacer to go between the yoke and frame.  I came home, adjusted the endshake slightly, and went out and shot 5 or 6 moonclips through it.  The ol' gun perked along just fine, so I think I'm back up and running. 

 

I am going to test it more this week (including our local Tuesday night USPSA match) to make sure everything is good before I trust using it at the Free State Championship next weekend in KC.  I have other guns I can use, if necessary.  

     

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Thanks for the reply. I’m one of those guys that tries to figure out “why”. I know what you mean about the “fitting”. I would do odd jobs for people and soon found out that all models weren’t necessarily the same and there were little tweaks with them even within the same model.  I do think that with the latest CNC machinery that parts are quite a bit more consistent than they used to be and that shows on more of the gun parts that interchange more freely. Glad you got her running again. 

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58 minutes ago, Carmoney said:

 

I can't tell where the fracture started.  I've messed around with it so much that the broken surfaces all sorta look the same to me.  

 

I suspect it's nothing more than metal fatigue over 15-20 years of heavy use.  I actually am quite gentle with my revolvers--my reloading technique does not involve the wham-slam moves that I see certain other shooters do.  Even at full speed, I open them gently, and I close them gently.  

 

I suppose it could have been caused by hot gases gradually cutting down from the cylinder gap, maybe?  This gun has never seen more than a few magnum loads, but I have shot a whole bunch of competition ammo (typically about 140 p.f.) through the thing.  I have dealt with a lot of revolvers over the years, and I don't believe I have ever seen this particular failure happen on any of them.  I'm going to chalk it up as a fluke event, I guess.  

 

One thing I have learned from this--there is a reason S&W insists on installing these at the factory.  There is nothing much involved in the actual "fitting" process, and they pretty much drop right in--but they apparently have made a ton of variations of yokes!  The stainless one that Toolguy sent me had a yoke barrel that was about .2" too short--not sure what kind of gun it came from--maybe a 625?  The blue yoke that MRBerg gave me was designed slightly differently (it came from a damaged 29 Classic), and initially it didn't work either.  But earlier this evening a machinist friend and I were able to fix it by fabricating a .06" stainless spacer to go between the yoke and frame.  I came home, adjusted the endshake slightly, and went out and shot 5 or 6 moonclips through it.  The ol' gun perked along just fine, so I think I'm back up and running. 

 

I am going to test it more this week (including our local Tuesday night USPSA match) to make sure everything is good before I trust using it at the Free State Championship next weekend in KC.  I have other guns I can use, if necessary.  

     

I’ve swapped a few yokes around just to see what the big deal was and found a pretty similar situation. My 929s almost all move around to any gun, and I know for a fact in my early days of shooting revos I would strip several 625s or 627s and just clean all the parts together and just put the guns back together and it was rarely an issue within the same generations and model. First time I’ve ever seen one break like that though. And if you have never seen it, I seriously doubt many of us will ever see it again.

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OK, so this is the modification we did to mate the M29 donor yoke to my M27-7 heater.  See that stainless spacer between yoke and frame?  That's what we made.  (Nothing exotic, just turned down the OD on a 5/16" flat washer, and held it on the belt sander until the thickness was right.) 

 

20220711_222244.thumb.jpg.864c66e351d92e7d09126f73de0ec2a0.jpg

 

Edited by Carmoney
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5 hours ago, Farmer said:

That’s a healthy amount.

 

Yes, around .06"

 

It's not a hyper-critical dimension, though.  The spacer just needs to keep everything in the right alignment so the cylinder can open and close normally.

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