Piston rod failure of a NYC Niagara (Oct 1949)

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Posted by Miningman on Thursday, November 22, 2018 5:05 PM

Good information. Have noticed you refer to the C1a on numerous occasions in several different threads. Too bad a prototype or a small run of them did not happen. Have to assume it was pretty darn close. 

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Posted by MidlandMike on Thursday, November 22, 2018 10:12 PM

...tandem rods.

I'm having a hard time trying to picture those.

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Posted by M636C on Thursday, November 22, 2018 10:59 PM



...tandem rods.


I'm having a hard time trying to picture those.


The rods were really in parallel rather than in tandem, thinking about the real meaning of the words. Tandem compounds had one cylinder in front of the other which is a correct use of the term.


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Posted by Overmod on Thursday, November 22, 2018 11:20 PM

The rods were really in parallel rather than in tandem, thinking about the real meaning of the words.

And it doesn't help that there are two different senses of 'tandem' applying to side-rod practice!  (Neither of these having anything to do with tandem compounds...)

The earlier approach, which I believe was first used in the 1920s, used a combination of fork-and-blade rods and concentric bushings to spread the effective thrust of the main rod between the main pin it worked on and another pin, usually the one in the following driver.

The type seen on the Niagara (and the original J configuration) has two parallel thin Timken rods sandwiching the big end of the main rod, passing back to sandwich a single rod at the following driver pin.  This puts all the thrust of the main in a straight line down three sets of drivers.  ("Tandem" here being two side-by-side, as if 'yoked', as opposed to two in line as on captain/stoker bicycles)

It is interesting to compare the rod layout of the original and 'revised' versions of the N&W J, which we discussed several years ago here.  That puts the big end completely outboard of the rod system, with only the valve eccentric crank further out. 

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Posted by Jones1945 on Friday, November 23, 2018 5:22 AM


What happened, of course, was that the improved Niagara turned out to be most of the things the C1a intended, without the drawbacks and compromises that the duplex 'state of the art' then involved. 

Thank you, Overmod. I find this thread from 2005 created by forum member feltonhill, he provided even more background about "the sketch in Trains magazine", I think he implied a sketch of a NYC C1a in the Trains mag but I am not sure if it was the same sketch I posted.

NYC C1a for UP829


"feltonhill : I located the book you referenced which had more info than the sketch in Trains mag. Thanks for the info! 

The drawing is dated 3/28/45. The Niagara test report was dated 7/3/48. Tests with 6023 were run 6/46 to 11/46. Tests with 5500 were run 6/47 to 11/47. As you can see, the tests were run after the C1a sketch was made. It was probably one of the considerations that came out of the design process for the Niagaras and Central's awareness of PRR's activity with the T1's. 

I have no "official" performance estimates for the C1a. I ran some of my own figures to see what if may have done. I assumed the same boiler as a standard Niagara, but with the increased 290 psi pressure noted on the sketch. 

In regular service, it would have been only a slight improvement over the Niagara as far as fuel and water economy is concerned. It would have had a higher DBHP output at speeds above 70 mph due to the improved steam distribution of four small cylinders. However, considering how conservatively the Niagaras were designed with respect to tractive effort and adhesion, the C1a would have been harder to handle under the usually-found variable rail conditions on most railroads. A pair of jointly controlled two axle engine sets is touchier than one directly controlled four axle engine. Baker valve gear may have helped because poppet valves could reduce back pressure to the point that there was little to help arrest a slip once it occurred (other than shutting the throttle and waiting until everything settled back down). IMO Central was wise not to bother with the C1a."

Speaking of wise, I would spend more time to study B&O's business strategies since the 1930s. Just try to be practical. Coffee



Regarding the 100mph thing......



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