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Steam & Excursion > Modified main drivers applied to older locos.Date: 01/29/25 12:23 Modified main drivers applied to older locos. Author: wcamp1472 At the waning days of larger orders for new steam locos, many RRs saw the benefits
of newer advancements in locomotive engineering.... and could add improvements, without adding a lot of increased costs. Locos, during their lifetimes saw maybe 2 or 3 extensive re-build and overhaul procedures, about every 5 years of service. One area that saw a lot of changes and improvements was centered around better counterbalancing and lightening of main and siderods. Early spoked drivers had counterweights that were 'best guesses' at compromise counter balance weights. The counter weight cavities cast into the driver centers, were hollow, and divided by hollow spaces between the spokes at the driver rims. The open cavities had molten-lead added, but probably will not fill the open cavities. With several spokes through the counterweight spaces, you'd have pockets, partially filled with molten-lead. In srevice, the neatly melted lead was pounded into a white powder, crowded at the outer limits of the cavities. Once the molten lead had cooled, steel cover plates were welded to cover the open-backs of the counterweights. One engineering concept that was developed in counterbalancing was mitigating the impact the mass of counterweights as the drivers increased in RPMs. Badly over-balanced counterweights could lift the whole driver, when the counterweight was traversing it's upper and lower circuits, at high RPMs. The drivers could lift the axle, when over the top, and add to ( double) the impact --- when closest to the rails--- and often might kink the rails where counterweights added that extra force*. So, design engineers added cross-counter-weights at the mating driver on the axle. The 'cross counterbalance' weight could be reduced in mass, if mounted at distance ( axle) from the main counter weight. Drivers fitted with cross-counter balance weights could be identified with small weights adjacent to the ends of the primary weights. Designers also calculated that they could shift the crescent-shaped cointerweights slightly off-center from the true-180-degree centerline commonly used to 'center' the counterweight--- in the days before cross-counterbalancing was adopted. So, you could have a cross-counterbalanced loco, but, with apparent out-of line position with it's crankpin. SOOO, let's get back to this loco... It has gone hrough an extensive rebuild. Adding the improved main drivers was a reasonable expense, and a performance increase. The new driver set uses a lighter, but stronger steel, wheel-center and the cross-counterbalacing is cleverly concealed. The newer cast steel driver-centers are lighter, and stronger, than the original, spoked wheel centers. The equipped engine would ride-smoother with the newer driver-centers, and they're easier on the tracks. Also, it was was common to retain the drivers that were NOT main-drivers. So, you will see the other drivers, on an up-graded re-bilild, will be the originals.... mainly because their counterweights were much smaller and lighter --- no need for 'modernization'.... They might have added other, additional improvements during the recent rebuild. W. ( * Reference, E.P. Alexander: The Pennsylvania Railroad, .. 1947 ). Edited 4 time(s). Last edit at 01/29/25 19:45 by wcamp1472. Date: 01/29/25 13:57 Re: Modified main drivers applied to older locos. Author: hawkinsun Wes, This topic always interested me. Locomotive wheels almost seem like sculptural artwork in their design. Very interesting castings that were probably pretty expensive to make. I wondered, at what point a railroad desided to replace just a set of main drivers, or do the whole set. When ballancing , I can see all the spaces in say GSC wheels where balancing weight could be added, but in the design of say, Scullin disc drivers, where did the ballance weights go ? Were these wheels cast with a front and rear, and hollow in the space between ? It would be fun to see all the different styles of wheel castings from all the manufacturers, including early spokes, and later spokes redesigned with strengthening webbing near the rim, like I've seen on Pennsy engines.
Thanks for all your informative posts. Craig Hanson Vay, Idaho Date: 01/29/25 14:56 Re: Modified main drivers applied to older locos. Author: Frisco1522 Date: 01/29/25 17:15 Re: Modified main drivers applied to older locos. Author: railstiesballast It is always a bit humbling to read your informative posts. We have to admire the design refinement
Date: 01/29/25 18:01 Re: Modified main drivers applied to older locos. Author: wcamp1472 When I first got up close, and volunteered on steamers,
I had thousands of questions ..... when I asked others, I got answers that did not make sense, or were plain false fabrications. So, my quest had always been to understand the principles behind apparently complex systems. And, I read all the sources I could find... I also had to be able to explain to others, what "work" I needed performed; and, and what to 'report' about apparent problems. My major area of RR learning remains understanding ---- and being able to explain train airbrakes. I'm still a "patzer"* at understanding train air brakes. W. ( "Patzer" = an incompetent chess player....) Edited 3 time(s). Last edit at 01/29/25 18:20 by wcamp1472. Date: 01/29/25 18:18 Re: Modified main drivers applied to older locos. Author: WrongWayMurphy This is my favorite steam locomotive, speedster 667 of the St L S-W .
It is no coincidence it too has all disc drivers like Frisco 724 above. ![]() Date: 01/29/25 20:51 Re: Modified main drivers applied to older locos. Author: weather Wes, greart info! What about BOXPOK?
Date: 01/29/25 23:34 Re: Modified main drivers applied to older locos. Author: Evan_Werkema wcamp1472 Wrote:
> Also, it was was common to retain the drivers that were NOT main-drivers. > So, you will see the other drivers, on an up-graded re-bilild, will be the originals.... > mainly because their counterweights were much smaller and lighter --- no need > for 'modernization'.... A couple of Southern Pacific locomotives in San Francisco, CA in 1956 sporting replacement disc main drivers while the others remained spoked: 1) 2-8-0 2864 (ex-Cotton Belt 768) on 61-inch drivers out-of-service in a deadline at Bayshore Yard. 2) 4-8-2 4354 on 73-inch wheels passing the Mission Bay roundhouse (and the westbound Coast Daylight) on eastbound commute train 140. Photos by E.K. Muller courtesy the Western Railway Museum Archives. ![]() ![]() Date: 01/30/25 01:17 Re: Modified main drivers applied to older locos. Author: wcamp1472 Re: 4354 loco
Notice the distinction between the sizes of the counterweights on drivers 3 & 4. Some supervisor has failed to ensure that the heavier counterweight on #4 driver is supposed to compensate for the combined weight of two halves of 2 siderods.... as found on #3's crankpin. Here, in the #4 position, it's more massive counterweight far exceeds the weight of it's lone siderod & crankpin. The #3 driver got placed in #4's axle position. It's heavier counterweight is more properly placed --- when at the #3 axle position. And, the lightest counterweight is more properly placed when at the #4's axle slot. Driver #3 has two-times the masses revolving around the axle.... there are ends of two siderods on one crankpin. So that weight of the 2 siderods would be better balanced with the heavier counterweight.... at the 3rd-axle position. The 'jointed connection' ( to #4 siderod), at #3's crankpin also adds more weight If properly arranged, driver #4 would have the lightest counterweight, of all the axles, since only one end of the last drive rod would be the lightest mass of the 4 axles . ( The no. 1 axle -drive wheel also has a correspondingly-light counterweight --- with only one side-rod end on it's crankpin). W. Edited 4 time(s). Last edit at 01/30/25 01:53 by wcamp1472. Date: 01/30/25 07:53 Re: Modified main drivers applied to older locos. Author: elueck The various applications of cast driver centers on the Texas and Pacific 2-10-4s of the 600 series is a study in itself. They went from just the main, to the main plus 1, or main plus 2 to all 5.
#650 illustrates the replacement of the main driver only. #604 illustrates the replacement of the main and #4 drivers #615 has only the #5 drivers replaced Edited 3 time(s). Last edit at 01/30/25 07:56 by elueck. ![]() ![]() ![]() Date: 01/30/25 08:00 Re: Modified main drivers applied to older locos. Author: elueck #608 illustrates the final form of the rebuilds.
New frame with cast cylinders. Replacement trailing truck replacing the Lima articulated trailing truck. All 5 drivers replaced with cast centers. ![]() Date: 01/30/25 09:39 Re: Modified main drivers applied to older locos. Author: wcamp1472 At the time that Lima designed and built the early version of the 2-10-4,
the technology for advanced, cast, one-piece loco frames had not been perfected or introduced. The trailer truck was pivoted behind the last driver with a frame cross-piece & pivot. The trailer truck was a rectangular box, and the drawbar was connected at the truck's rear cross bar, to the drawbars and tender. In pulling-power applied, all the forces tend to keep in-line, pulling the load. The design of these trucks doesn't handle shoving moves, in reverse, very well. If, however, you're attempting to shove against a heavy train, the drawbars from the tender apply sidewise thrusts to the trailer-truck frame, and only the 2 wheel flanges of the truck ( and the rail), keep the truck in-line. When there is too much force, applied at an angle, to the tracks, it can result in derailing the trailer truck. Too much force applied --- against a heavy train--- , and the weight and shoving-force of the train is applied to 2 outer flanges of the truck --- and it slips up & over the rail-head, and you're "on the ground" It took several years and several failures and variants, before cast, one piece, steel loco frames were produced and successful. They made several attempts before they got enough angular bracing to confine the cylinders. Early attempts at cross-bracing cracked early in testing on heavy trains. Finally, GSC got enough steel at that cross-joint, that torsion cracks never appeared. As far as I know, these giant castings are the largest steel castings produced..... Like C&O/PRR 2-10-4 and ATSF 2-10-4 locos. Large, articulated locos used 2, smaller cast frames, with draw-pins between the 2 frames. W. Edited 1 time(s). Last edit at 01/30/25 11:48 by wcamp1472. Date: 01/30/25 09:56 Re: Modified main drivers applied to older locos. Author: tomstp T&P found out the hard way that their 2-10-4's could not back thru the switches of Dallas Union Terminal. They could run thru them forward. Like wise on many industrial switches. That kept the 2-10-2 engines on the roster way past years when they normally would have been retired.
Date: 01/30/25 15:27 Re: Modified main drivers applied to older locos. Author: Frisco1522 I like the 608.Delta truck, roller bearings and disc drivers. I'll bet she was a good fast freight engine.
Date: 01/30/25 18:55 Re: Modified main drivers applied to older locos. Author: rmusselman Hello, the Reading G3s built in 1948, as I recall, had Boxpok main drivers and spoked on the others, as built new. Likely the frugal Dutchmen at the Reading shops used the same drivers for the 1st and 3rd axles as other G classes. Did they have roller bearings on the axles
Cheers! Posted from iPhone Date: 01/30/25 19:15 Re: Modified main drivers applied to older locos Author: timz B&O 4-6-2 5304 got Kuhler streamlined and Boxpok, then lost the Kuhler and at some point lost the Boxpok too. When it was restreamlined postwar it had traditional spokes. (Crossbalanced, tho.)
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