I read in the new MR about steam locomotives. The article said that the trailing truck was incorperated to support larger fireboxes. Is there a huge compression spring between the truck and the firebox?
Just curious,
BB
I think there are usually a pair of sliding support plates (one on each side) on top of the trailing truck frame, that support plates under the rear frame of the locomotive. The Firebox is supported above the rear frame.
Or, on some trailing trucks, the firebox was supported directly from the truck frame using a pair (one on each side) of centering devices with rollers to allow the truck a bit of sideways movement while still supporting the firebox.
That may not be exact, but it’s probably close.
Regards
Ed
I’m not sure about the latter case in Ed’s post, but he pretty much nailed the first, about flat bearing surfaces that were greased … First, there was the pivot for the truck, a heavy bushing on a machined pintle. Then, somewhere between the wheels, flat machined surfaces that slid against each other to support the firebox.
If you have a BLI large steamer, it has a small wire coil spring on a pintle to force the trailing truck to track well against the rails. I didn’t like the dip that my Hudson cab made over the trailing truck, so I cut a ball-point pen coil spring to see if that might prop up the cab and make the loco appear to be more level. Long story short, the old spring is back in 'cuz the other spring, even cut down considerably, was too strong and lifted the rear drivers right off the tracks. I haven’t given up on the matter, though. I’m determined to win this one…somehow.
Now that is a question I’ve wondered about too, as model locos just have them swinging on a small spring loaded bar whithout any support from above, I pondered over where the weight was transferred to the wheels, good question.
On some model locomotives, the weight IS transferred to the trailing truck. This is not a good thing, since this weight is tractive effort that is removed from the drivers. Athearn’s 2-8-2 and 4-6-2 are good examples of this. I bought a pair of Athearn Mikes for general freight service and was very disappointed in their lack of pulling power. The stock loco, with tender, weighed 16.5 oz. I added weight to the boiler and frame areas, bringing the weight up to 20.0 oz. This was dis-
tributed so that the total weight of the locomotive was balanced about a point mid-way between the 2nd and 3rd drivers. Before ballasting, this loco would pull a 28 oz. train up the ruling grade on my Erie Northshore sub. This train con-sisted of 3 loaded Athearn 2 bay hoppers and an Athearn bay-window caboose. After adding the extra 3 1/2 oz. of weight, there was no change in the locos pulling ability. (I always use Athearn hoppers like this, loaded with a loose coal made from locomotive traction grit, to test the pulling power of new or recently modified engines. In actual service, one such hopper is equal to two regular freight cars.) Some time after these disappointing results, I read about removing the spring on the trailing truck to increase tractive effort. After doing so, the Mike was able to drag one additional hopper up the 2.5% (on a curve) grade. While this is an improvement, the two Mikes will still not move the required 12 hoppers plus caboose over the division and have been assigned to lighter duties. Any suggestions for further improvements would be welcomed. In the meantime, a couple of Grand Valley 2-8-0’s (Bachmann 1914) have been delegated for this train: when required, a couple of cars of general freight can even be added to the train.
Wayne
On a prototype loco, the trailing truck frame is spring supported off the wheels, and then the firebox/rear of the boiler is usually supported on a sliding plate arrangement similar to the pad portions of a semi tractor trailer truck fifth wheel.
On a model the trailing truck is there for looks and accuracy, but any load it supports is going to detract from the tractive effort available as noted above.