Re: Side Rods

Posted by Mike Trent on Jun 22, 2018; 1:26pm
URL: http://c-sng-discussion-forum.254.s1.nabble.com/Side-Rods-tp11906p11909.html

Hi, Keith.

As steam locomotives evolved through the late 1800's, the science of physics advanced, and improvements relative to greater tractive effort and efficiency took root in the steam locomotive accordingly.

By 1897, it was accepted that one of the ways to increase both of these areas was to use the 3rd driver on a 2-8-0. This allowed, because of the longer length to the crankpin, a higher level of efficiency.  1897 was the year the B-4-E class was built. The following year, the B-4-F class engines were built by Brooks for the C&N ry, and they also employed use of a third axle main driver.

There are different ways to calculate tractive effort on a steam locomotive, but length of the main rods is not generally considered. Rather, boiler pressure, bore and stroke of the cylinders, and driver diameter are the typical factors.

On D&RGW narrow gauge 2-8-0's, it is interesting to consider the C-18 and C-19 classes. The C-18's were rated in the conventional way at 18,000 lbs TE, hence C-18. The C-19's, which included three engines which were leased to the C&S in 1936, were rated in the conventional way at 19,000 lbs TE. The D&RGW was phasing out the C-19's because it was found that the C-18's, which had the 3rd axle as the main driver, pulled their tonnage better than the slightly heavier C-19's. That is why C-19's were available for lease. On the C&S, engine crews constantly complained that the C-19's couldn't pull tonnage nearly as well as the B-4-E class, which was also rated at 19,000 lbs TE, despite having added half flanges to the blind drivers. The C-17's were classed the way they were because they were likely a bit smaller. The C-18's may have been classed in the way they were to differentiate them from the C-19's, as they probably could have been rated at 19,000 lbs.

At the time the B-3-C's had been rebuilt from the old Cooke design, the main rods were not changed in position.

I don't know why the SP Northern you have on your desktop had the main driver at #2, but they must have done it for a particular reason, possibly for a certain area of their system where that worked better. The UP "800's", which I would consider the Gold Standard of Northerns, had the main drivers at #3. The third series of 800's was built in 1944.