First, the ejector rod on your model 66 uses a left hand thread. Because of this it's possible to tighten the ejector rod with the cylinder closed. To do this you will need some fingernail on your left hand thumb, if you're a nail chewer put a bandaid on that thumb for a couple of weeks so it can grow out.
If there are any unfired cases in the cylinder you'll have to exercize extreme caution and make quite sure that your muzzle is pointed in a completely safe direction because this will require cocking the gun and releasing the hammer with the trigger repeatedly. Wedge your left hand thumbnail FIRMLY into the knurling on the ejector rod. Then start cocking and releasing the hammer to rotate the cylinder while you keep the ejector rod from turning with your thumbnail. After enough turns of the cylinder it will tighten enough that you can then open the cylinder.
Note, if you've used locktight on this, you may not be able to apply enough force to keep the ejector rod from spinning. In this case, it will mean a trip to a gunsmith, a real tounge lashing, and probably a new ejector rod and possibly having a new extractor fitted to the gun. As someone who once lived in the greater Cleveland area, using locktite on something like this junction is what we would refer to as Polish Engineering. Basically, locktite isn't called for and it's a bad idea that will just create more work down the road.
Worst case, what will be required if the ejector rod won't turn in with fingernail pressure is having a small pin TIG welded to the ejector rod so that a higher degree of force can be used to get it to thread back into place. If that won't do it, the ejector rod will have to be cut from the gun using a small end mill in a milling machine. However, this would mean that the ejector rod has unscrewed WAY out of the extractor and that normally won't happen with just one loading of the cylinder.
In most cases what will be required is opening up the sideplate, removing the hammer and cylinder bolt, and using a corectly bent piece of heavy wire of the correct diameter to push the locking pin far enough that the cylinder can be unlocked at the front. Once that is accomplished, a small screw driver can be wedged into the front lock to keep it clear and the wire withdrawn to the point where the cylinder unlocks at the rear. Then the cylinder can be opened, the crane removed, and everything can be put right. If it sounds a bit fussy, it is.
When properly tightened, the ejector rod will NOT shoot loose. The key is to properly tighten it so that it doesn't work loose. Basically, it's about as tight as an average person can achieve using one hand on a large handled # 3 Philips head screw without grunting it tight. BTW, a # 3 philips head is a LARGE screw recess and #3 screwdrivers are a bit larger than normal.
What I like to do is grasp the cylinder, loaded fully with fired brass, firmly in my left hand and use a bit of worn out leather belt folded over the knurling and grasped by some old fashioned pliers. As for how firm a grasp, picture shaking hands with a returning Marine without attempting to start a grip contest. In simple terms, a good firm handshake firm that says you respect his effort. This will act as a slip clutch so that you don't damage the threads. If you find it still tends to shoot loose, picture a larger and taller Marine and use a firmer grip on the cylinder. Once it's tight enough, just leave it be. BTW, until you've found just the right feel, make sure to check your cylinder rod with a finger test each and every time you reload at the range and stop shooting as soon as you feel it's loose. It's also a good idea to take some pliers and a screwdriver for the crane screw to the range so that you can re-tighten it at the bench until it stops shooting loose.
If the above just won't prevent it from shooting loose, the threads on the ejector rod or the extractor may be damaged to the point where both parts need replacing. If that's the case, have a gunsmith or S&W replace the parts and fit the extractor to the hand to make sure it times properly. Do NOT use locktite, you'll just create more expense and work, either for yourself or a subsequent owner of your gun.
