Cylinder stop height adjustment for full notch engagement?

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OlongJohnson

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Read the FAQs, did a search, didn't find what I was looking for. I'm going through a new M&P 340 and cleaning it up, deburring, etc. For example, I just finished addressing the three long ratchets the factory gave it. Bonus metal...

Anyway, it's a Centennial, so it will only be fired and dry fired DA. One goal is to minimize cylinder notch peening. I measured the protrusion of the cylinder stop from the frame, the depth of the slots in the cylinder, and the clearance from the cylinder to the frame. It looks like I have ~0.010 of cylinder notch depth that isn't engaged by the cylinder stop.

There's plenty of trigger pre-travel before it picks up the stop, so I could adjust the stop to sit upward ~0.008 or so in the frame. Still wouldn't be bottoming the stop in the notches, but would have a little more engagement of the stop against the side of the notch, increasing the contact area when the cylinder stops rotating, thereby reducing the stress on the side of the cylinder notch and theoretically reducing any tendency for peening to develop. To put numbers on it, I would increase the engagement of the stop in the notches from ~0.037 to 0.045, slightly more than a 20% increase, but due to the shape of the stop, the increase in contact area would be even more. Seems worthwhile if there are no negatives associated with it.

(The gun does time and lock up correctly, no rotation in either direction. I'm just talking about maximizing engagement to optimize durability. Also, I'm not going to type an essay about it, but given what I've just been through fixing on this gun - and a bunch of other S&Ws I've worked on - the notion that S&W built it right in the first place and I should leave it alone is fully hydrophobic.)

Is this a thing that is regarded as worth doing? Is there any problem I haven't figured out that would arise if I do that?
 
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When I started fooling with guns back in the 70’s, the more I learned, the more re-engineering I thought I could do... with LEO as my profession, I attended armorer’s school for S&W, HK, Glock and Sig. I learned that interchangeable parts were designed to work in several models thus having a range of adjustment that could be accomplished. Some parts are R&R as in remove and replace with no smithing due to the time it would require an employee to “fix” a part rather then just replace a part. I also learned that guns have life expectancies and when enough parts wear, they are beyond the time cost of repair and therefore deemed “worn out”. Keep in mind that continuous repairs do not sell new guns and profit is the bottom line. This is a round about way of indicating that most every gun out there could possibly be improved but at what cost? The gun in question, a DA pocket pistol the OP owns sounds like it works fine but the OP wants to maximize the life expectancy. A noble thought and if not on an employer’s time clock, a worthy experience. To the OP’s question, just consider the cylinder weight of a J frame being turned DA with or without casings or ammo in the cylinders has a minimal effect on any potential “peening” due to weight force of metal to metal. If this was a larger frame with larger (heavier) parts then that effect must be considered. My last point was made by one of our instructors that most every part that makes up a revolver works in conjunction with other parts and the modification of one may or will affect other parts either in a positive or negative manner. In summary, a critical fine tuning with everything working in exact concert may not be possible and why tolerances are acceptable.
 
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In my experience, severe peening of the stop notches is more of a sign of abuse than normal use, and unless the stop won't hold when tested while the gun is at rest, additional engagement may not be necessary.

No problem that I can see with removal of material from the adjustment step on the cylinder stop, as long as the interface/timing of the bevel and the trigger hook would not be negatively affected. In terms of your desired outcome, I'm not sure the adjustment step, if totally removed, would give the ball of the stop the additional height desired.

Without looking at the gun, speculation (by me) about timing problems caused by doing this would be just that......but it might be best to have a replacement stop handy just in case.


 
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Another point is that peening of the stop notch if and when it occurs, can be remedied with a small hammer with a polished face. A couple taps on the raised metal on the edge of the stop notch will move it back down. I have a "pre" model Highway Patrolman, that showed it had a lot of rounds through it when I got it. I tapped down the peening on it. Bu, you could see very distinct casing marks on the recoil shield. it was butter smooth etc. Now there you have about as heavy as cylinder as there is that had cycled a whole bunch of times.

Like others said a J frame cylinder doesn't have much mass and will take much longer to peen, Plus, your less apt to cycle the cylinder on a J frame as fast as often as an N frame 38/357 simply because you have deal with it being lighter and more difficult to aim and operate.

Plus, a minor amount of rotational "looseness" on a revolver that isn't being used for precision shooting isn't an issue unless it spits lead. As the bullet leaves the cylinder throat it enters the slightly opened forcing cone and as it does the bullet will move the cylinder into perfect alignment for the bullet to finish moving into the barrel.
 
I applaud your efforts to fine tune your revolver whether or not the potential for peening the notches is an issue. It's your hobby so your time and effort doesn't matter, it's the fun and satisfaction.

The one caution I offer to be aware of is this:

Do not raise the cyl stop ball higher than the trigger hook is able to lower the ball in the frame slot and be flush. You don't want the ball higher than flush with the slot in the frame window when retracted, to score or drag on the cyl anymore than they already do. In other words don't raise the ball any higher than it now measures below the surface of the frame slot at full retraction.

Hope that helps and let us know your results,
 
Changing the height of the stop only changes the end point of its travel, which is the location where the trigger will pick it up and starts moving it. The geometries that determine the relationship between the stop position and the trigger position are not affected. Once the stop moves past its original end of travel point, the timing and geometric relationships from there throughout the rest of the trigger stroke remain unchanged.
 
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I agree totally with the other revolver smiths in that it is not needed and can lead to other problems to have the cylinder stop raising to the ultimate depth of the notches. What I would do and did in tuning was to use a hard Arkansas stone to 'break' the leading edge of the cylinder stop just enough to minimize the track oft left around the cylinder when some cylinder stops 'drag' on the surface of the cylinder.
 
The Kuhnhausen book says to give yourself an extra .005" cylinder stop height after fully engaging. This is to be sure that the stop doesn't roll by. The other thing would be to make sure you have a good cylinder stop spring that would also help this.
I bought a used model 29-5 that had a little cheesy mim stop with a short ball. Guess what? It left peeing on the cylinder stop slots. Once I installed a power custom oversize stop with the extra .005" height, the peening ended. Cylinder stop drop timing can be effected by removal of material from the top of the stop adjustment surface. The stop must hit the cylinder prior to the cylinder stop lead. I suggest you get and read the Kuhnhausen book before proceeding.
 
I have the book, and read it before going to the internet.

p. 69 of Kuhnhausen says:

...the next step is to check for and adjust the cylinder stop to full vertical cylinder stop/cylinder locking slot engagement plus an extra .005" and then check for possible cylinder roll/backroll disconnect.
Click to expand...

It's not obvious to me what is meant by "full engagement." Is it make the cylinder stop "bottom" (upward) into the notch, then an extra .005" so that when the cylinder is swung out, the stop is .005" higher than the deepest point of the notch? (That seems logical to me.) Or is "full engagement" defined as enough to lock the cylinder in each direction, and then add another .005"?

When you installed the Power Custom stop with the extra .005" height, what was your measurement reference for making that adjustment? i.e., how did you determine "full engagement" in order to add .005"? Was it just .005" higher than the original one?

Next point, it's not obvious to me how drop timing would be altered by adjustments to the height adjusting pad. Once the trigger picks up the stop and begins moving it, the height adjusting pad has zero influence on any geometric relationship that would determine timing.
 
Full engagement to me is what you first stated.

There is a visual clue with the sideplate off and looking at the gap between the top adjustment surface of the stop and the bottom of the frame at the stop window. You can see if there is a gap or not, a gap would mean the ball of the stop is bottomed in the cylinder. You can fit and measure the gap with a feeler gauge.Then when you open the cylinder there should be no gap as the stop then moves to it's highest position. This is all dependent on the stop being clearanced properly to fit the cylinder slots and hand window without dragging or high spots.

Also anytime you mess with a cylinder stop it is imperative to check the barrel cylinder alignment with a range rod!
 
1. Full engagement means the top of the cyl stop ball just touches the bottom of the cyl notch (determined with machinist ink) when in its highest position. Adding .005" to its height means the ball is under spring tension pressing against the bottom of the notch. And the adjustment step is .005" from contacting the frame at the bottom of the cyl stop slot.


2. Raising the stop ball by relieving the adjustment step surface also pivots the entire cyl stop part upwards under spring tension and of course the notch at the bottom (for the trigger hook) upwards as well. That's what changes the engagement geometry of the trigger hook to the cyl stop. If that trigger hook notch is pivoted upwards enough, the trigger hook will no longer fit into the cyl stop hook notch w/o putting downward pressure against the bottom of the notch, thus keeping the ball from raising to its full height.

Someone not realizing that, keeps filing more off the adjustment step but the ball doesn't rise!

So you may have to relieve the bottom edge of the hook notch somewhat for the hook to fit into it w/o putting downward pressure on the cyl stop. Removing material in the bottom of the notch is how the downward travel of the cyl stop ball by the trigger hook can be affected/lessened. The ball may stick up above flush with the cyl stop slot in the frame and drag on the cyl.

I hope that helps,
 
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Hondo44 said:
1. Full engagement means the top of the cyl stop ball just touches the bottom of the cyl notch (determined with machinist ink) when in its highest position. Adding .005" to its height means the ball is under spring tension pressing against the bottom of the notch. And the adjustment step is .005" from contacting the frame at the bottom of the cyl stop slot.
...
I hope that helps,
Click to expand...

Thanks, that does help. That's the reading of Kuhnhausen that made the most sense to me, it just wasn't airtight. One other factor that led to doubt was the drawings in the book show the engaged stop ball not touching the bottom of the cylinder notch.

I would expect the clearance at the adjustment step to be about half the over-engagement of the ball in the notch, though, due to the motion ratio (the adjustment step is closer to the pivot pin).

As it all worked out, I ended up not making any changes. I had watched the ball rise into the notch a few hundred times while dialing in the ratchets, but the side plate was on for that. When I took the side plate off and looked at the engagement of the stop ball with the frame window, it was clear that raising the stop ball at all would reduce its engagement against the side of the frame window. (The end of the ball hook was already even with the lower edge of the window.) Since the frame window is softer than the cylinder and more expensive to replace, I left the adjustment alone.

Will review if I ever mess with a bigger frame size.
 
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