Guys,
These single ball bearings are a "fix" (similar to the added dimple now added to the top plate of motor trucks for F-3 and Geeps 7&9) that has the effect of reducing the depth to which the "worm" on the Pullmor motor shaft meshes into the "worm wheel" pressed onto the shaft joining the driving wheels.
This change was associated with the change from a metal "worm wheel" to a plastic one. A basic problem with plastic gears is that their plastic gear teeth are only about 1/10th (one-tenth) as strong as metal gear teeth. (Yes, I know that some gear metals are weaker than others, and there are some very strong plastics, but 1/10 fits the situation in these engines well-- I recently looked very carefully at that. It seems I have some experience in very strong glass-plastic composites; I was a research assistant running an investigative research program while I was a grad student in engineering.)
What happens is that the purveyors of plastic gears, like what we have here, like to sell them as replacements for metal gears. But to do this, there is the problem of weakness to overcome. All the more so, because a case that can be made that the metal gears were already overloaded (remember that the 1st Berkshires had two worms and two worm wheels to handle the motor torque, as did the original F3s for many years). I could find no product which would be a satisfactory grease for the one worm/one worm wheel (all metal) which turned two axles in the Geeps, Trainmasters, and later F3s, all with the vertical Pullmor. (The required number is around 600; 300 to not quite 400 was all I could find; Red & Tacky was only about 315, IIRC-- well, tacky is good, even essential. Lionel postwar grease may have approached 400, but I have no data for it, and today I can't find any commercial source. The numbers are for kinematic viscosity at 40 degrees centigrade.)
So the weakness of the plastic teeth is typically made a lesser factor by increasing the base width of the plastic teeth. Since the worm itself was not changed, this makes the two sets of teeth interfere with each other unless the spacing between them is increased. This will at some point cause problems which must be investigated: lack of continuity of gear action (one gear will cut into the tooth tops of the other); lack of true involute action (uniform motion is not transmitted, leading to higher stresses on weaker teeth and thus earlier broken teeth).
Some data: Lionel gears in the mentioned diesels are for spur gears associated with the vertical motors are 40 dpi (diametrical pitch inches) with a 20-degree pressure angle. At some time in the middle 1950's this angle changed from the 14-1/2 degree pressure angle which had been standard; I do not know exactly when Lionel changed over. Plastic gears are typically made with a 25- or 30-degree pressure angle. I doubt that in this situation the "fix" would accommodate more than an increase to 25-degree pressure angle in the plastic worm wheel. (Spur gears with the two pressure angles run only with considerable drag, as I demonstrated to myself by using newer geared wheels driven by a train of older gears (the motor truck became very hot and seized after about 15 minutes of running.) The 25-degree tooth has a strength increase of about 2/3, so it's about 1/6 the strength of a 20-degree metal gear (a 30-degree plastic tooth would be about 1/4).
There is no standard for worm gears, but small wormsets as here are often made with crossed helical gears, and that is the case here. There are several ways to cut helical gears, sometimes using spur cutters, sometimes special cutters; the later worm shafts I believe were not cut but deformed into blank shafts of adjusted diameter by roller dies. (As Earle Buckingham wrote, there are 100 ways to produce an involute tooth profile; I adapted some moving bridge designs to test enclosed gearsets proposed by Earle Gear Company in actual service (locks and main drives except sector gear)). Plastic gears of course are not cut but injection-molded in a die-- the die is expensive but in sufficient number the gears are cheap. In theory, a very accurate tooth profile could be produced-- this is true for spur gears, but no method for worm wheel gears is known, some degree of running in is always required.
The worm can be taken as a rack by taking a slice along the centerline (the full method for continuity of action requires several parallel sections. offset along the pitch of the worm, say at least 5, which is a real pain). Then the teeth of this rack have straight sides. The worm wheel teeth have curved sides (a lot of them are simplified to straight sides, particularly plastic gears in model rr work with 1-thread worms). This can be awkward here with a 3-start worm and non-locking ratio ~8:1.
The tooth size on the metal gears is about the same as the 40 dpi spur teeth, but the thickness of the gear is greater to increase the contact line and the continuity of gear action (1.0 is a minimum). The metal worm wheels, being of the softer metal, wore or flowed to a line contact from the initial point contact of crossed helical gears. This does not happen with a plastic gear wheel although there may be some elastic deformation to a more limited extent. The mineral filler in plastic can be abrasive (tiny fibrous rock crystals) and may wear the worm. These wormsets are open, which is a difficult lubrication condition.
The helix angle is about 30-degrees. I have found that making a drawing works best for this type of analysis. Grid paper with 10 squares to the inch can be used to draw the teeth and their mesh to a scale of 10 times enlargement, or even 20 times, can be used. Drawing the rack is easy, but the teeth of a wheel gear have to be done by drawing the unwinding of a string off the base circle. This line must make a 25-degree angle (plastic wheel gear) with the line of centers when it crosses it. The line of centers to a rack (worm gear center here) is at a right angle to its axis. For addendum, try the usual 1.0 pitch; for dedendum, same plus clearance, try 1.2 pitch for small gears. The wheel gear segment could be cut out of a copy and rolled along the clearance line. Metal gears can be shown using 20-degree pressure angle.
I will explain the results when I have them, but I'm not likely to be very fast with this. Those with a little time can try the procedure above. I've meant to do it for several years now.
Does anyone know whether the heavy scale GG-1s, first edition of some years back, have metal or plastic worm wheels? I'm not anxious to take one apart just to see. How is factory lubrication in these-- present, or sometimes not present? (Just repeating reports for other engines.) Present GG-1? TIA.
--Frank M