what I found on my S&W M66 from Jim's post

D

Dill

New member
here's what I found wrong with my revolver after reading Jim's very thorough post. It seems my revolver may need a 'shim' as mentioned in that post. Is this something a qualified gunsmith has to do. I know there was some confusion about this, so I thought I'd post a picture of what I was talking about. The arrow points to the 'gap' created when pushing the cylinder towards the back of the gun..which is then closed when I push the cylinder fowards.


cylinder.jpg
 
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I'm not sure I understand what's going on. Do you mean that when the cylinder is OPEN, it moves back and creates a gap at the front???

If so, there is nothing wrong with your gun. What regulates backward cylinder movement, when in the open position, is the cylinder stop lug at the lower rear of the frame window, on the right side. This is the small circular lug that prevents the open cylinder from moving so far rearward that it would fail to close properly.

These are hand fit at the factory, and some are fitted longer than others, so there is a little more backward movement possible. All revolvers will show this gap when in the open position.

The only time a shim is needed, is when there's a problem with the CLOSED cylinder. If there is too much fore-and-aft movement in the closed cylinder, the gun has "cylinder endshake". This condition can be corrected by first trimming the cylinder crane's shaft, then fitting a hardened stainless washer, or shim.

As you described it, you have no problem with your gun, this is entirely normal.
 
thats exactly the problem, is it exibits the same front to back play closed, as it does open. There is enough play that when you move it back and forth, it makes a slight 'knock'
 
That's called endshake, and it may or may not be a problem.

It's normally a result of the gun being shot a fair amount with full-power loads, or a TREMENDOUS amount with light loads.

It's really not a problem until you start having ignition problems.

It can be fixed with either a washer or two (relatively easy), or by stretching the crane by peining or with a special tool, then recutting it for length. That is a lot more complex, requires tools, and is normally a job for someone who knows what they're doing.
 
What's the model number of your gun, including the dash number?

My 686 is a 686-1, & is covered by S&W's lifetime warranty. Now, that is supposed to be for the original buyer only but I would give it a try. S&W might fix it for free.
 
Well, that's either a 66 or a 66-1.

It'll say which on the frame cutout behind the crane when you open the cylinder.
 
Dill: the cylinders develop endshake from rotational wear between the crane end and the cylinder surface. The end of the crane tube has a small surface area and a lot of pressure on it. On mine, the end of the tube wore a groove in the cylinder face as the end shake progressed (over about 10,000 rounds). You may need to smooth the inner face of the cylinder where the crane tube rides on it before installing a washer. SW will "stretch" the crane tube on their machine and refinish it to remove the shake, so you don't need a washer. Proabably worth it if you want to keep the gun. Lubing the end of the crane tube with a good grease (like Tetra) each cleaning will really cut down on the wear.
 
Don't get too excited about that gap between the yoke and the gas ring on the cylinder. All S&W's have that to a greater or lesser extent. The end-shake is no real problem till it gets really loose.
I have two PPC revolvers built on mod-10's. One has around 2 million rds through it (I bought it used, its been through 3 previous owners and is on its 3rd barrel, it has a great deal of end shake, but it is still capable of shooting Master class scores), The other is a newer one I built in 1996 that has about 300,000+ rds through it and still delivers 1.5" groups at 50yds off a rest, and still gives me scores in the 1490's. It is nowhere near as tight as when new, but the accuracy is still there.
If you are really concerned about the end-shake, take it to a gunsmith that has experience with S&W's. If he says its excessive (It probably isn't- it took 3,500rds of .357 max. handloads to shoot a M-19 I carried in late '70's "loose", -plus a whole bunch of .38's, S&W fixed it for free) send it to S&W and they'll fix it either for free, or for a whole lot less than a free-lance gunsmith. They will either stretch the yoke or will install/fit a new one. Usually less than $75.00, plus the outrageous shipping cost now neccessary.
 
Also, I forgot to mention:
The wear is usually not from the rotation of the cylinder. If the gun is lubricated at all, the friction here is minimal. The wear is from the battering from the vibration and set-back from firing the gun. The greater the recoil and pressure, the greater the plastic deformation (stretch) from the firing forces, and eventially the hammering of the yoke and rear cylinder bearing surface and the contact on the recoil plate (face of frame). As the yoke becomes battered, the rate of increase accelerates as the end shake becomes progressively larger.

The shim method of correction is better than stretching as the stretching alters the heat treating of the already rather soft metal in these parts, so a stretched yoke gets "skwozed" back down quicker than if it was corrected by shimming. I have personally heard Ron Powers describe this, and if the gun needs correcting (I doubt it), then other than sending it back to the factory, shimming is the prefered method.
Powers is the only source of the shims that I'm aware of, and are cheaper through Brownells than directly from Ron Powers.
 
I just checked the frame behind the crane. All it says is 'Mod 66' no -1 or anything.


How much play is acceptable here? I do have some feeler gauges, and could measure?
 
Bounty,

Endshake is much less a function of rotational wear than it is of inertial battering from recoil. That's why heavier loads cause endshake much more rapidly than light loads.
 
And it's this "battering effect" that explains why I recommend checking endshake (at full lockup, mind you) on a gun you're thinking of buying.

As John Kilgore rightly points out, "some" limited endshake won't degrade performance much. And a small amount will be found on many brand new guns these days (sigh). But all else being equal, you want less :).

The advice to have a gunsmith determine how bad your case is, is worthwhile. And I too vote in favor of shimming, for the reasons stated.
 
"Endshake is much less a function of rotational wear than it is of inertial battering from recoil. That's why heavier loads cause endshake much more rapidly than light loads."

Depends what you're shooting. I shot nothing but light 115-gr .38 target loads through my 686 and it still developed about .004" end shake across about 15k rounds fired. In my case it was friction wear because I wasn't lubing the end of the crane tube (just the side surfaces) because I didn't know any better at the time.

After I installed shims, I started lubing the end of the tube with grease (tetra or Slide Glide) and the progression of end shake seems to be zero. I suspect a very good grease has enough film strength to help reduce the battering effect as well as the friction wear.

BTW: To anybody considering shims: you will need to re-surface the inside face of the cylinder where the crane tube rides before installing the shim. There will be a groove there from the tube end and the shim will not fit into the groove because it is slightly larger than the end of the tube's inner dimension. If you install a shim and re-assemble without smooting down the ridge of the groove, the cylinder will bind up tight and you may bend the crane.
 
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