Lionel 8702 Southern Crescent Locomotive Driving Wheel Diameters

That is by design so the engine would navigate 027 curves.

Thanks Chuck. That makes sense. It's hard to imagine such a big locomotive operating on 027 track. I am going to try running it on an 027 layout to see how well it does.

The design of this loco is derived from the postwar 2046 and 646.  My cousin brought his 2046 to our house when we had O27 curves, and it worked just fine (but with a ton of overhang.)  I don't have a postwar large Hudson handy.  But my guess would be that the center driving wheel is also slightly undersized relative to the flanged end wheels.

Ted - the middle driving wheel diameter is 1.338". The forward and trailing driving wheel diameters are 1.392". All three axles are coplanar, so with the naked eye you can see daylight under the middle driving wheel. It is quite noticeable.

This is a really nice locomotive - very powerful, but the smoker isn't too effective, and I don't understand why this locomotive doesn't have a horn.

Have you ever replaced the headlight incandescent bulb with an LED bulb?

@Mossback Mike posted:

I don't understand why this locomotive doesn't have a horn.

Do you mean whistle?

@Bob Paris posted:

Yes. Why wouldn't Lionel include a steam whistle or some sort of air-horn sound with this locomotive?

They didn't have a whistle because at the time the locomotive was made, 1977, they were 'in between' developing an electronic whistle. the first attempt at an electronic whistle was in the 8206 4-6-4 in 1972. It really wasn't too bad, but the design of the circuit board wasn't compatible with postwar transformer whistle control and was dropped after one production run. (Along with the C&O 8204 4-4-2 of the same time period.) It wasn't until 1980 when Lionel finally perfected the electronic Sound of steam and whistle with the 8003 Chessie 2-8-4 to be used with a postwar transformer. Lionel thought at the time a whistle sound really wasn't that important to operators. So, the 8702 was in this 'dry spell'. Lionel did supply instructions in 1980 to add the new whistle and SOS board to older locomotives like yours and the Blue Comet and the 8600 and 8306, and 8900 4-6-4 engines.

All of Lionel's postwar Magne-traction Hudsons used the same wheels, which had a 2035- part number.  I just dug around my workbench and found a 2055 chassis.  I only have a dial caliper so my measurements aren't as precise as yours, but the flanged end wheels measure about 1.37".  The blind center wheel measures a little more than 1.35".  So the center wheel IS smaller on postwar locos and you can see a little daylight under it.  But the difference isn't as pronounced as what you're reporting.

The first 6-drivered locos of the MPC era were the 8206 and 8603 small Hudsons.  These used die-cast "Baldwin Disc" type drivers.  When Lionel MPC re-introduced  the 2046-style Hudson with Magne-traction in 1976, it was equipped with spoked drivers.  The similar 8702 Southern appeared the following year.

I guess it's possible that the wheel dies were so worn by 1976 that MPC had to commission new ones.  If that's true, I don't understand why they didn't make them to the same dimensions as their postwar predecessors?  The driving wheels on the 8600 are lighter in color than postwar wheels, so they might be made of a different ferrous material, but I never noticed the size difference.  @Chuck Sartor  @PaperTRW  do you know what really happened?

Thanks Ted. I think I might eventually swap out the old Lionel SOS board with a new ERR steam railsounds board. I installed one of these in a Marx tender, with a tethered connection to a Marx 666 locomotive. It was a fun project. The hardest part was mounting the reed switch. I wont have to worry about that with the 8702 because I'll just use the existing signal from the proximity switch that is part of the smoker assembly.

If the gap bothers you, you could always install the motor assembly from a postwar Hudson, they all run on O27.  Of course you would have to paint the sidewalls white yourself!

The 1970s smoke units contain a pair of contacts that momentarily supply full track voltage to the Sound of Steam circuit in the tender, triggering a burst of static.  I don't believe the reed switch supplies full voltage, so be careful not to burn anything out.  If you get it to work please post back!

@Ted S posted:

If the gap bothers you, you could always install the motor assembly from a postwar Hudson, they all run on O27.  Of course you would have to paint the sidewalls white yourself!

The 1970s smoke units contain a pair of contacts that momentarily supply full track voltage to the Sound of Steam circuit in the tender, triggering a burst of static.  I don't believe the reed switch supplies full voltage, so be careful not to burn anything out.  If you get it to work please post back!

Ay Caramba! Thanks for the heads up. Maybe I'll just use the reed switch & magnet instead.