Difficulty removing hex head screw from drivers to replace traction tires

You are turning the crankpin.  What you will wind up doing is removing the driver from the axle, pressing out the crankpin, lightly knurling the pin, and re-inserting.  If some Loctite got on the machine screw threads, some serious heat will release it.

You might try the heat before sending the mechanism to Joe - if there is enough friction left in the press-fit, then maybe . . .

If you can get the crankpin partway out without removing the driver, try a teeny bit of shaft Loctite on the pin, then reinsert and wait 24 hours before trying again with the wrench.

I just had one of these through here - a Museum MTH had the crank pin come completely out of the driver.  This is apparently not uncommon.

I don't understand, whats the crankpin?

I'm not sure what you're trying to remove?

Personally I hate rubber tires, they are unnecessary and should be optional.  But the last time I did this job it required a 5mm socket driver to remove the hex head screw holding the side rod to the LAST driver only.  Once the side rod is loose you should be able to slip the tire between the rod and the wheel.  Then work it around the circumference of the wheel and into the groove.  It must be FLAT.

Not sure why you would be messing with the crankpin, although I disagree with Bob. Those wheels are pressed on tight at the factory.  Unless you're half gorilla, I can't imagine you getting it off its axle with hand tools.

Feel free to disagree - we have had three such failures.  You do need a wheel puller.  That's why I suggested the mechanism would have to go to Joe.  Joe also knows how to quarter the driver, which is an essential step at reassembly.

A crankpin is generally a steel pin of sorts, on which a connecting rod exerts force. The steel pin on a model locomotive is a cylinder, pressed into the driver, and drilled/ tapped for the crankpin screw.  Generally, a crankpin cap is what keeps the rod on the pin.  This is basic for model train mechanics, which is what the OP needs about now.

Automobile, airplane, lawn mower, and steam locomotives all have crankshafts, and the part the rod bolts on is called a pin, no matter how big it is. On a steam locomotive, the crankshaft doubles as, and is called, a driver assembly.

I am not sure if it is a crank pin or just a sleeve. (Since some drivers don't have a bearing surface, the side rod screw has the bearing surface).

But Bob is saying the screw may not be turning rather a metal sleeve pressed into the wheel that has threads is turning.

Or, it is possible it was over tightened and the side rod screw is stripped and can't screw out naturally.  If the latter you can try turning with pliers while pulling out at the same time.  If it is the sleeve or crankpin that is turning it may partially or fully come out also, but it would be best to have the other side rod screws and eccentric crank removed so that the side rod comes off when you pull the stuck screw out.  Since the threaded sleeve will keep the screw attached to the side rod.   G

It turns out the rear set of drivers have a typical hex head screw that I finally was able to coax out. The front set of drivers had a sleeve that finally came out when I applied a slight outward pressure while turning. It appears to be a friction fit rather than threaded. Very odd and I have never encountered it before. The engine is an early version of the GN R2 articulated from about 2000. 

The screw is still stuck in the sleeve so you can grip the sleeve and get the screw out.  Than do as Bob stated to get the Sleeve reinstalled in the driver.

Normally you don't need to take all the screws out.  Just the screw in the traction tire wheel, and loosen the next closest to give a gap to get the tire in.  G

Bob I'm sorry I didn't mean to be rude.  Now I understand the situation.

Yes if the crankpin comes all the way out of the wheel, the original poster might have to remove the wheel to reattach the crankpin properly.

I thought you meant that by turning the crankpin, this would remove or loosen the wheel on its axle.  I don't have an R2, but every MTH loco I have has the wheels firmly pressed onto axles which are captive in the frame.  At least some of this nonsense could be avoided if the frame were designed properly with pedestal binders or a "bottom plate," so the wheels and axles could be removed as a set.

What I meant was that it would take a strong puller or some careful work with a punch to get the wheel off; I don't believe it will come off by accident even if the crankpin is completely removed.  Sorry for any misunderstanding.  -Ted

I have run into this a few times on articulated locos for some reason. What I did, once I realized what was happening, was to rotate the driver so I could push gently on the back of the screw and crankpin, and gently levered out the screw and crankpin, I then staked the crankpin, held it with a small pliers and removed the hex head screw, using heat if necessary; once the two are separated, I put the crankpin in the freezer for a while to shrink it a bit, dabbed a little Loctite red on the outside of the pin and pressed it into place and let it set up overnight. I then put on the new traction tire, and started the hex head screw, just tightening it a touch more than finger tight. Too much torque is no good, as you can understand when you see how small the threads are. All the screw does is hold the rod to the driver, so less is more when tightening. you can always tighten it s a bit more if needed, but once it is too tight....