UP Big Boy Tender Tender Type: 14-wheeled Water Capacity: 25,000 gallons Fuel: Coal** 56,000 lbs.
But far from the ‘biggest’. In perspective the ATSF tenders we were discussing are substantially heavier.
We aren’t counting tenders with ‘water bottle/A-tank’ auxiliary water tenders. I don’t offhand know the exact weight of the ‘tender’ that 3985 toured with, or the one that 4014 currently uses, but the added ‘water car’ would have substantial tare and loaded weight. Of course if the restored 2926 were to tour, they could use a comparable range-extending auxiliary tank… and remain ‘biggest’…
Incidentally I cleared up the ‘eccentric main pin’ thing in PM, but for anyone puzzled: the main pin on a reciprocating locomotive with the sort of Timken rods on a PRR T1 is mounted to produce the shortest possible stroke before the metal between the main pin and axle holes becomes too thin for distortion or cracking in service – this is what determines the ‘throw’ of the side rods at 26". On a normal engine this also determines the stroke of the mains.
For very high speed some designers want the stroke of the mains to be shorter than the throw of the rods (for balance reasons covered in references like Ralph Johnson’s). This could easily be done by cranking the main pin… but this would make it impossible to service the side-rod roller bearings without pressing the main pin out of the wheel, not a good idea for a great variety of reasons.
What Baldwin noticed, and Vauclain described to the audience in the presentation from Atlantic City, was that on a duplex engine the thrust from a main is low enough that a smaller main-pin diameter can be used for the corresponding roller bearing. Normally when the main pin is machined, this smaller diameter would be concentric with the inboard bearing diameter. Baldwin instead machined it ‘eccentric’ so that when the main pin is installed in the wheel, t
For very high speed some designers want the stroke of the mains to be shorter than the throw of the rods
I believe this was a feature of the Ivatt “Alantics” of the English Great Northern Railway. 1898 was a little before Timken bearings were a consideration, but the Atlantics were the first fast express locomotives on the GNR that had coupled axles, so they may have thought deeply about balance…
Peter
I should probably have been clearer: the idea is to be able to get the ‘inside’ rod (and its brass) off without having to pull or manipulate a ‘cranked’ pin.
Conversely to normal American practice, the eye or at least the bushing bore of the main rod has to be smaller than that of the side rod. This is much less a concern for the Timken lightweight rods than for solid construction with adequate plain bearings.
The Ivatt engines had a 6" diameter journal for the side rods and 5" for the main, implying an axis offset of ½" for a stroke difference of 1" (23" vs. 24", which appears appreciable when augment stresses at high cyclic are concerned)
https://www.gnrsociety.com/locomotive-class/c1/
Going back to the T1s, I’m ticked because there was a drawing right in the coverage of Vauclain’s remarks that showed the detail of the pin, and I can’t find it to post an URL or cite. There are certainly drawings in the T1 Trust engineering repository but I can’t link those here.