I gotta ask....ejector rod threads

[Hair Trigger]

I think I know the answer, but want verification from the S&W gurus here who do know. On almost every S&W revolver model starting in the late 50's, one of the first series changes was to change the ejector and rod threads from right-hand to left-hand thread. Why was this done? Were the right hand threaded rods more prone to loosening and backing out from the guns being fired?

One reason I ask is, I have to re-tighten the ejector rod on my M57 almost every time I open the cylinder after firing it, or at least checking it to make sure it is tight. My M29-2 extractor screw was loose when I bought the gun, and I haven't fired it (nor do I think it's been fired). Both guns have left-hand thread.

 

[bulletslap]

With RH threads, when the ejector rod loosens it tends to bind up the ejector rod as it lengthens overall and prevents the cylinder from opening.

 

[Doc44]

A little Loctite will solve the loosening of the extractor rod on your Model 57. You refer to an extractor screw being loose on your 29-2, what part is that?

Bill

 

[Protocall_Design]

With RH threads, when the ejector rod loosens it tends to bind up the ejector rod as it lengthens overall and prevents the cylinder from opening.

It does the same thing with left hand threads.

 

[armorer951]

As an armorer, I would not recommend putting Loctite or a thread locker product in this particular location. Even when the "correct" product strength and amount is used, it can cause great difficulty in disassembly if and when repairs become necessary.

There are several different styles of specific tools available for this job. Clean the ex. rod threads and the threaded extractor cavity with alcohol or Gun Scrubber and follow the directions provided with the tool.

A drill chuck also makes an excellent tool for removal and re-installation. Be sure to insert some empty casings into the cylinder chambers before tightening or loosening the assembly.

 

[Hair Trigger]

A little Loctite will solve the loosening of the extractor rod on your Model 57. You refer to an extractor screw being loose on your 29-2, what part is that?

Bill

I'm the one with a loose screw, I meant the extractor rod. I discovered it being loose when I spun the open cylinder with it while cleaning the gun.

As an armorer, I would not recommend putting Loctite or thread locker product in this particular location. Even when the "correct" product strength and amount is used, it can cause great difficulty in disassembly if and when repairs become necessary.

There are several different styles of specific tools available for this job. Clean the ex. rod threads and the extractor cavity with alcohol or Gun Scrubber and follow the directions provided with the tool.

A drill chuck also makes an excellent tool for removal and re-installation. Be sure to insert some empty casings into the cylinder chambers before tightening or loosening the assembly.

I am hesitant to ever use a thread locker on one of my firearms, unless I've seen evidence it was used by the factory. I've cleaned the threads on the rod and examined them under a 10x loupe, there is no residue of any sort and the threads are in perfect shape. When you say "extractor cavity", do you mean the recess in the barrel shroud, or the portion of the extractor that the rod threads into? If the latter, do I need to remove the cylinder, or just completely unscrew the extractor rod, remove it and the spring, and pull the extractor star from the cylinder?

The drill chuck sounds great for tightening the rod, gives more torque application than just twisting the rod with fingers, and won't slip (as long as appropriately tightened) like a pair of pliers would. That's the other thing, I can't make myself use a tool on it to tighten it up.

I still didn't get the original question answered. Why was the thread changed to left-hand?

 

[armorer951]

The thread direction was changed to discourage the rod from unscrewing further if it became loose during use. Only marginally successful. (see response #2)

Degreasing the threads just helps the parts stay put when tightened. This should be done to the threads on the extractor rod, and to the threads inside the extractor itself. If the threads are clean, and the proper tool is used, the assembly should not come loose.

 

[Doc44]

The thread direction was changed from right-hand to left-hand when S&W received reports in 1959 the extractor rod on 44 Magnums (only this model as far as I know) was loosening due to recoil and locking up the cylinder, thus preventing the revolver from being opened. The company decided to change the thread direction on all K and N extractor rods and extractor stems and issued Engineering Directive #586 on December 22, 1959. The reason for the change: To prevent extractor rod and extractor stem from loosening. Depending on the model, it took nearly three years to implement.

Bill

 

[Hondo44]

I still didn't get the original question answered. Why was the thread changed to left-hand?

When there are rotational forces at work in mechanical systems, like the bullet being forced thru the rifling twist, at 15,000 to 50,000 PSI, threaded parts that rotate in the same plane like screw threads can react with opposite forces. A barrel not tightened sufficiently for example, will actually unscrew, even pinned barrels a slight amount. Just enough to see that the front sight is no longer straight up and down.

So rotating mechanical devices that involve screw threads in the same plain often have left hand threads if they tighten in the opposite direction of the revolving forces of the mechanism, which is often the case.

So in a revolver, with a left hand threaded extractor rod, the forces of sending the bullet down the barrel will actually work to tighten the screw threads instead of loosening them.

 

[DWalt]

My theory is the cylinder turns CCW when viewed from the rear due to the hand pushing on the ratchet in the center of the extractor star. The extractor rod does drag a little on the spring-loaded catch in the barrel lug. If the rod thread has a RH thread, the normal CCW movement of the cylinder has a tendency to unscrew the extractor rod, lengthening the assembly. Shortly thereafter, the extractor rod will bear tightly against the barrel lug, tying up the cylinder, preventing it from opening. However, the opposite happens if the extractor rod has a LH thread. It will then tend to tighten.

If the extractor rod, either RH or LH threaded, is screwed down very tightly, then nothing bad happens. But if even slightly loose, a RH threaded rod will lengthen and jam the cylinder, preventing it from opening.

I have found that the best way to keep a RH-threaded extractor rod from unscrewing is to put a tiny dab of clear nail polish on the threads, let it dry, then screw the rod in place tightly. It will not come loose on its own. If you ever do need to unscrew it, just soak the assembly in Acetone, which will dissolve the nail polish in fairly short order.

 

[BC38]

My theory is the cylinder turns CCW when viewed from the rear due to the hand pushing on the ratchet in the center of the extractor star. The extractor rod does drag a little on the spring-loaded catch in the barrel lug. If the rod thread has a RH thread, the normal CCW movement of the cylinder has a tendency to unscrew the extractor rod, lengthening the assembly. Shortly thereafter, the extractor rod will bear tightly against the barrel lug, tying up the cylinder, preventing it from opening. However, the opposite happens if the extractor rod has a LH thread. It will then tend to tighten.

If the extractor rod, either RH or LH threaded, is screwed down very tightly, then nothing bad happens. But if even slightly loose, a RH threaded rod will lengthen and jam the cylinder, preventing it from opening.

I have found that the best way to keep a RH-threaded extractor rod from unscrewing is to put a tiny dab of clear nail polish on the threads, let it dry, then screw the rod in place tightly. It will not come loose on its own. If you ever do need to unscrew it, just soak the assembly in Acetone, which will dissolve the nail polish in fairly short order.

^^THIS^^
With right hand threads the direction of the cylinder rotation will UN-screw the ejector rod.
With left-hand threads the cylinder rotation will tend to TIGHTEN the ejector rod.
Simple as that.