Endshake in S&W 686 revolvers

Is there a factory specification for acceptable cylinder endshake in a new 686? Is there any difference in acceptable endshake in early revision numbered revolvers as opposed to later revision numbered revolvers?

Historically any End shake over 0.002 inch should be corrected. Because the farther that the cylinder can move under recoil the more the cylinder can act like a slide hammer and do more damage at a higher rate.

Note, just to be very clear to someone who may be new to revolvers End Shake is NOT the movement of the cylinder when the yoke is open. When the cylinder is open the normal movement can range between about 1/32 to 1/16 inch and this is not a problem. End Shake is the difference in the Barrel/Cylinder gap with the cylinder pressed towards the barrel and with the cylinder pressed towards the rear. I'll also note that the total amount of pressure applied to the cylinder during this test shouldn't exceed about 5 lbs, the newer revolvers use a spring loaded yoke screw that can be "sprung" a bit and possibly damaged by excessive force on the yoke during an End Shake measurement. On older revolvers you should also feel for movement at the fitted surfaces at the front of the Yoke Frame interface because that can cause a false reading of high End Shake that is actually due to a worn or improperly fitted Yoke Screw.

My Toy said:

Is there a factory specification for acceptable cylinder endshake in a new 686? Is there any difference in acceptable endshake in early revision numbered revolvers as opposed to later revision numbered revolvers?

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Spec on endshake is .000" - .001" doesn't matter rev number. Measure by using a feeler gauge to measure barrel cylinder gap with cylinder pushed forward and pulled back.

bountyhunter said:

Spec on endshake is .000" - .001" doesn't matter rev number. Measure by using a feeler gauge to measure barrel cylinder gap with cylinder pushed forward and pulled back.

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That would be a tad too tight. Others will chime in with the correct specs.

sodacan said:

That would be a tad too tight. Others will chime in with the correct specs.

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They can chime away, but what I posted is correct. Read the Kuhnhausen service manual, page 26:


"Install the cylinder and recheck for end shake. Trim the yoke face carefully until approximately .001 end shake remains."

Like I said, zero to .001" is optimum. If it gets beyond .002", you shim it. That's why the shims come in .002" size.

Thanks for the replies.

Zero endshake is definitely not optimum, nor advised by Kuhnhausen, who suggests approximately .001" endshake as ideal; zero endshake and firing rounds are a recipe for binding due to thermal expansion.

To answer OP's question: 1) I don't think any of us knows what current factory specs are for endshake; 2) endshake that's either ideal, tolerable, or in need of correction is functionally the same throughout revisions.

Kuhnhausen, again, states that ideal endshake is approximately .001", and that gross cylinder endshake is "enough play so that the cylinder hits or drags the barrel, or somewhat over .006"."

Hapworth said:

Zero endshake is definitely not optimum, nor advised by Kuhnhausen, who suggests approximately .001" endshake as ideal; zero endshake and firing rounds are a recipe for binding due to thermal expansion.

To answer OP's question: 1) I don't think any of us knows what current factory specs are for endshake; 2) endshake that's either ideal, tolerable, or in need of correction is functionally the same throughout revisions.

Kuhnhausen, again, states that ideal endshake is approximately .001", and that gross cylinder endshake is "enough play so that the cylinder hits or drags the barrel, or somewhat over .006"."

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"Approximately .001" translates to .000 - .001" because the accuracy of measurement on end shake is about .001" since it is done using feeler gauges, and it should not exceed .001". Ergo, the cylinder is adjusted so that there is sufficient play to have no binding (which is just above zero) and not to exceed .001". As I said: the target spec is 0 - .001" (obviously without drag or binding which would mean an interference fit).

As for what SW currently does: the new revolvers I have worked on showed that the end of the crane tube is set up loose and then swaged and trimmed in to get proper fit. New revolvers should have zero end shake. For the record, all revos loosen up on end shake with use so setting it on the loose side to begin with just accelerates the time to when you have to service it to correct it.

EDIT TO ADD:

I can answer what a new SW end shake is because I just went in and measured it. I have a PC 627 with only about 100 rounds fired through it that I bought new a couple of years back. I measured the cylinder end shake as follows:

I used a machinist's feeler gauge set which has gauges in .001" increments from .001" to .015" and also some "halfs" like .0015" and .0025" to be able to get half thousandth readings.

1) I first measured the barrel cylinder gap with no pressure applied to the cylinder. .004" was a "loose fit" and .005" was too tight. I used a .003+.0015 to get .0045" and it was "just snug" fit.

2) With the .0045" gauge in place I pushed the cylinder forward (toward barrel) and moved the gauge but did not feel any tightening up on the gauge fit. I pulled the cylinder back away from the barrel and again felt no change as to the gauge's snugness in fit.

Based on that, it shows no detectable change at all in cylinder position pushing front to rear which means no significant end shake, ie the end shake is very close to zero (definitely far less than .001" which would have easily been seen in the measurement method since changes of 1/2 thou caused a significant change in the tightness of the gauge).

That seems to show that the "factory" setting is to get the end shake as close to zero as possible without any binding. It is clearly not .001" on this new 627, it is very close to zero.

bountyhunter, you stated "because the accuracy of measurement on end shake is about .001" since it is done using feeler gauges".
I would suggest that you use a ten thou micrometer and some feeler gauges so that you can see the resolution of a feeler gauge. It is closer to one ten thousandth than one thousandth. Once you learn the feel of the drag, using a micrometer to learn, your accuracy is around 2-3 ten thou. and even better with much practice.

Stu
retired Mercedes mechanic and user of feeler gauges

bountyhunter said:

"Approximately .001" translates to .000 - .001" because the accuracy of measurement on end shake is about .001" since it is done using feeler gauges, and it should not exceed .001". Ergo, the cylinder is adjusted so that there is sufficient play to have no binding (which is just above zero) and not to exceed .001". As I said: the target spec is 0 - .001" (obviously without drag or binding which would mean an interference fit).

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Kuhnhausen's quite clear that the target is .001", not .000" to .001"; a measure of endshake needs to be dialed in to mitigate the potential for stacking tolerances, just like a measure of slop in the cylinder rotation on lock up is part of the design. His several pages of discussion on correcting endshake with either shims, peening, or a combination repeatedly target .001"; less than that is never mentioned.

I can answer what a new SW end shake is because I just went in and measured it. I have a PC 627 with only about 100 rounds fired through it that I bought new a couple of years back. I measured the cylinder end shake as follows:

I used a machinist's feeler gauge set which has gauges in .001" increments from .001" to .015" and also some "halfs" like .0015" and .0025" to be able to get half thousandth readings.

1) I first measured the barrel cylinder gap with no pressure applied to the cylinder. .004" was a "loose fit" and .005" was too tight. I used a .003+.0015 to get .0045" and it was "just snug" fit.

2) With the .0045" gauge in place I pushed the cylinder forward (toward barrel) and moved the gauge but did not feel any tightening up on the gauge fit. I pulled the cylinder back away from the barrel and again felt no change as to the gauge's snugness in fit.

Based on that, it shows no detectable change at all in cylinder position pushing front to rear which means no significant end shake, ie the end shake is very close to zero (definitely far less than .001" which would have easily been seen in the measurement method since changes of 1/2 thou caused a significant change in the tightness of the gauge).

That seems to show that the "factory" setting is to get the end shake as close to zero as possible without any binding. It is clearly not .001" on this new 627, it is very close to zero.

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If a single data point can be used to divine "factory spec", then my new J-frame -- which arrived with .014" barrel-cylinder gap -- is by-the-book S&W?

And why didn't you use the correct method to gauge endshake?

As an armorer, I've always thought of examining a revolver for "end shake" as a diagnostic tool for determining a possible out of specification condition....and not just an arbitrary measurement that has to be dealt with on it's own. While this very close (.001") or "zero" gauge is critical and desired when the revolver is first assembled and fit, the constant evaluation and constant maintenance of this close tolerance in the "real world" of normal wear and regular use seems quite unnecessary, as long as the proper recommended front and rear gauges are maintained.

The cylinder inevitably moves forward with use (wear). This progressive movement will cause the rear gauge or headspace to increase and the front gauge, or B/C gap to decrease. The existence of cylinder end shake, the gauge between the end of the barrel of the yoke and the bearing surface inside the cylinder, then becomes an indication that there may be an out of spec. condition in either the front, rear or front and rear cylinder assembly gauge.

Since some gauge (cylinder end shake) is necessary for the cylinder assembly to work properly, (open, close and rotate) it follows that if the front and rear gauges are correct, or are within specifications, then the end shake present would be incidental, and would not affect normal function.

If excessive end shake is found, then this conditon certainly warrants further examination and evaluation (measurement) of the front an rear gauges to determine if they are within specifications. If the headspace and B/C gauges are within spec, then the arbitrary removal of all remaining end shake seems unnecessary, and may in fact interfere with the assemby's ability to accomodate necessary lubricants and inevitable dirt and debris.

Endshake discussions are always a can of worms...

On the "newer" guns with the spring loaded plunger in the yoke screw, minimize the yoke endshake first with the yoke screw removed. There are shims for this.

Now you can set the cylinder endshake. I like squaring up the end of the yoke and using shims rather than stretching the yoke. I do it even on new guns as the shim(s) make for a better bearing surface and the gun will stay in spec longer.

.001" endshake is fine on .44 or .357 mags firing magnum ammo, they'll stay in spec better, but will make the gun a bit fussy. If you can feel any endshake you have at least .002" endshake.

I set my .38 special and .45 acp revolvers up with .002" to .003" endshake. When they "grow" to .004"+ I add a shim. It's a matter of practicality.

617s etc get set up with .001" endshake to help me get a light DA pull with good ignition (rimfires are the most difficult) and I deal with checking for crud under the "star" regularly.

YMMV

I definitely agree using the shims is an improved bearing surface. They are much harder and slicker than the steel end of the tube and will wear much slower. The crane tube end will wear a groove into the cylinder over time and it seems to happen faster with stainless guns (I assume the steel is not as hard). Anyway, installing washers slows the rate that it loosens up.

"If you can feel any endshake you have at least .002" endshake."

Maybe, but I have seen it on guns that measured .001 so I think it is detectable. The point I was making is I never see end shake on new guns. I see MANY other defects on new guns but it appears that SW does set the end shake correctly. The cranes I have seen on new guns show what appears to be swage marks on the end of the tube. I suspect they cut the tubes a shade short and assemble, measure end shake, then swage whatever distance is needed so that it is "dead on" with one operation rather than multiple trim and checks. Anyway, whatever they are using I am not seeing loose cylinders on new guns here.

As for cylinders binding, never had one but then I don't shoot my guns until they are so hot they glow in the dark. The guns I have seen that bind usually have an accumulation or dirt, crud and carbon under the head of the extractor star causing it.