Hey has any body ever notice the hammer efect on o gauge steamer?

Wow fun thread. I'll jump in to get ripped apart as well.

As for toy trains, any hammer blow seen from the 90 degree crank offset and the light weight model drive rods would be  incredibly small.  Also since the actual drive is through some form of gear reduction from an electric motor its just not the same thing. If your engine is wobbling look for a mechanical problem. 

irl cross balancing does work on two piston locomotives up to the design speed.  However even a reasonably well maintained large steam locomotive will show much higher forces at the rails then a diesel electric consist of similar horsepower.  Reference ace 3000 research trials with c and o 614.  Also many European locomotives had 3 and 4 cylinder drive to reduce the weight of the drive rods and spread out the force applied locations to every 120 or 90 degrees.  Big UP 12 driver engines had 3 cylinder drive in the US . 

The baby is back to sleep  now so I'm going back to bed . 

The hammering of a poorly balanced engine most certainly could and did damage the track.  Frisco's spot series 2-10-2 drag engines were limited to 35 mph, faster than which they tended to kick the rails out from underneath them.  Joe Colias relates a wonderful story about one of them doing it on a curve in the middle of a high trestle over the Big Piney River.  The Operating and Plant Departments hated those engines and turned most of them into 4-8-4s.

I don't think you'll see the effect on models because the hammering starts from of the explosive exspansion of steam in the cylinders forcing the driving the main rods against the pins and therefore the drivers against the rails.  Since our models don't drive the rods through the cylinders in pulses, the forces aren't there, even in miniature.

Very entertaining reading from the resident engineers, particularly the disagreements.  Kinda reminds me of my earlier IT career within the aerospace & semiconductor testing industries when the design engineers & machinists would argue with each other on whether a design on paper will actually work once it's fabbed.  Good cheap entertainment! 

I have been analyzing and designing dynamic systems since 1966.  If the analysis is done correctly, it will predict the performance of the hardware very closely.  Recently I have done the analysis and design for several gyro stabilized precision gimbals.  My analysis has predicted the performance of the gimbals quite accurately.  The rule is this:  If the analysis predicts it will work, you have a chance.  If the analysis predicts it won't work, don't even try.  I have redesigned systems for which no analysis was done.  Once the system was redesigned and a proper analysis was done, the system worked.  

Were there analytic tools in the '50s that could analyze a steam locomotive?  Yes.  They were called analog computers, and commercial, electronic analog computers became available in 1949.  Mechanical analog computers were designed in the '30s and are still available today.  Commercial digital computers were not available until 1955, and they were very slow,  too slow to solve this problem.