I’ve noticed on my Mantua 4-6-0 Rogers locomotive, and on my MDC old time 2-6-0 that the rear set of drivers is placed much further back on the locomotive. What is the purpose of this? Also was it only done to six wheeled steamers or where there others that this was done to as well? Thanks for all the wonderful help guys.
Dave
The rear drivers were set further back to support the extra length of the locomotive. As for your second question, I don’t know.
EspeeC9,
The Southern Pacific GS-4 (actually, all the GS-series engines) had extra spacing between the first set of drivers and the second to allow for an Alco lateral driving box, used to relieve stress on the front drivers and reduce flange wear. When the engine entered a curve, the flange pressure would exceed a certain amount and the box would allow the main bearing on the front driver to move to the side, allowing the second pair of drivers to share in the thrust. (From “Those Daylight 4-8-4’s” by Robert J. Church, page 15.) This book also contains schematic drawings and extensive pictures showing the difference in driver spacing.
I have read where the three cylinder engines had a larger spacing between the first and second driver also, but this was for clearance of the center piston rod (over the axle of the first driver set) to the eccentric crank on the axle of the second driver. I have not seen blueprints or schematics of this arrangement.
Mark C.
On the Rogers loco, the rear coupled wheels were set back to allow space for the firebox and ashpan, which were placed between the frames to give adequate depth. I gather the MDC model is largely freelance, but the same reason applies.
You’ll also find that spacing on some older 2-8-0s, for the same reason. Other 4-6-0s and 2-8-0s had the firebox on top of the frames, but still had a slightly larger gap between the 3rd and 4th axles, to allow room for the components - slides or links - that secured the firebox to the frame, and in some cases the equalising beams between the spring hangers, particularly on older BLW-built 2-8-0s.
You’ll also find many 6 and 8-coupled designs with a larger spacing between the first and second coupled axles. This was to allow space for inside Stephenson valve gear - look for the rocker and valve rod to the valve chest.
All the best,
Mark.
Really? Odd then, that there were many 2-6-0s and 4-6-0s with equally spaced coupled wheels…[;)]
The extra spacing between the second and third driver was only done on 19th century locomotives. Eventually, the engine designers realized that pushing the rear driver forward and using a trailing truck to support the rear of the locomotive created an engine that could operate at higher speeds because it allowed room for a deeper and wider firebox. The PRR eventually went the other way when they replaced the trailing truck on their Mikado with an extra driving wheel to make their famous decapod. They achieved a remarkable drawbar pull (over 90,000 lbs) with only a slight reduction in speed capability.
The three cylinder arrangement didn’t last long, partially because it was a maintenance nightmare. But mostly due to the fact that it didn’t contribute a significant boost in power.
Look at the particular type 10 wheeler he’s talking about. You’ll see that the design had extra length to it due to the fact that it had a firebox between the frame rails. Many locomotives had the firebox supported on the frame rails. here’s an example in this next quote.
Wrong, on both counts.
Yes, I pointed that out in my initial response to your nonsense post.
The next quote is from me, correcting your comments.
Really? Only 19th century locos? You might want to check your facts…
WRT 3-cylinder locos: On the New Haven RR, they had almost simular 4-8-2’s, called R-2a’s and R-3’s. The R-2’s were two cylinder, while the R-3’s had three. The R-2’s were 362,500lbs while the R-3’s were at 374,000lbs. Same driver size (69"), same boiler pressure (265lbs), same grate area (70.8 sq. ft.), built the same year in 1926 by Alco. The R-2’s had two 27x30" cylinders, while the R-3’s had three 22x30" cylinders.
The operating dept. loved the R-3’s. From “New Haven Power”, by Jack Swanberg, page 184-185. “Listen to retired General Road Foreman Bill Copeland as he lights up when he thinks of his many years on these locomotives: The three cylinder engines had a terrific draft; the sound was chickety-chick, chickety-chick; one strong and two light…They could run like a scared cat, and pull an awful train at high speed. They could take 5000 tons up the Shore Line while an R-2a might take 3500 tons at best…and coming west out of Boston with 125 empties, how they would come!”
So why did almost identical locos have such different performance if it wasn’t that third cylinder?
Paul A. Cutler III
Weather Or No Go New Haven
Mark:
I think that Jeff was mainly talking about 3-cylinder American locomotives, which, unlike British locos, were never really that successful. ALCO was able to adapt the British Gresley 3-cylinder design, but the third cylinder always tended to run hot, possibly because of the weight of the locos that it was used with–the UP 4-12-2 and SP and UP 4-10-2 locos, for example. I know that the 3-cylinder design was very successful with British locos (and probably most British exports), but that might have had to do with their lighter design.
Baldwin also experimented with a 3-cylinder design (not the Gresley, which was copyrighted by ALCO) which consisted of a double eccentric gear on the engineer’s side of the loco to activate the third cylinder. Their most notable usage was on the Rio Grande 1600 series 4-8-2’s and their own experimental #50000 4-10-2, but by and large, the 3-cylinder locomotive in America was not the resounding success that it was in Britain and other countries.
As to the odd driver spacing on 4-6-0’s, I can only say that from my observations of the Southern Pacific ten-wheelers, it was to support a long, narrow f
I stand vindicated. Long-time trains unlimited fan.