4-4-0 rods

[joegideon]

Question:  The (prototype) Ma & Pa 4-4-0s, as well as most other 4-4-0s have their side rods OUTSIDE of the main rods.  It looks funny- but I looked at plans and photos of the Ma & Pa engines on the 'net and in a 1965 M.R., as well as other 4-4-0s on my  roster- a PFM V. & T. Modern Reno, an Alco brass model of one of these same engines (#6) and a brass S.P. E23 by Fujiyama... ALL run the side rods OUTSIDE of the main rod.  The Spectrum models have the main rods configured convetionally- Main rod outside... I believe it would be easy to move the rod- hopefully, it wouldn't cause the crankpins to back out. 

[Jim Banner]

In the real world, side rods outside cause more of a dynamic imbalance than side rods inside.  As well, side rods outside is possible only if the main rods are to the lead driven axle (as on your 4-4-0.)

On the model, putting the main rods outside allows spacing the cylinders a little farther apart which may be required to let the front truck swing enough to negotiate the tight curves we model railroaders all like to use.

I would expect the brass models to get it right, but then I would not expect the brass models to run on 15" radius curves.

[ebtnut]

Joe is correct that many, if not most, 4-4-0's had the main rods inboard of the side rods.  I believe PRR 1223 at Strasburg is this way as well.  If you want to "correct" it, it should not be a big deal.  You'll need to get a longer crankpin screw for the rear driver (probably the same screw as the front driver crankpin) and then find a piece of brass tube or small washers to bush out the side rod to keep it square to the crankpin. 

[caboose101]

An interesting observation about the outside side rods.  Just a prototype note about the Ma & Pa.  With nearly 500 curves between York, PA and Baltimore, it took old Nos. 4, 5, and 6 about 5 hours to cover the 77 miles.  With a cruising speed of 20 mph, dynamic imbalance was not the concern it might otherwise have been.

Regards,

Caboose101

[Jim Banner]

The Ma and Pa may have been limited to 20 mph by the trackage, but some 4-4-0's were capable of speeds up to 95 mph. 

[paustinsmith]

Well that is something I never noticed. As best I can determine, the MDC 4-4-0 has the main rod outside.

Peter Smith, Memphis