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4-4-0 rods

Started by joegideon, February 03, 2007, 04:56:44 AM

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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.
Growing older is mandatory but growing up is optional.

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. 
Growing older is mandatory but growing up is optional.

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