Big Boy Locomotive

I went to see the Union Pacific No. 4014, a Big Boy locomotive, at a whistle stop in Greeley, CO, October 23, 2024.

Gigantic

Honestly, pictures don’t convey the impression of bulk it gives. I’ve been around the No. 4005 Big Boy at the Forney Transportation Museum in Denver. A working locomotive seems even bigger.

Noisy

Between whistles, bells, mechanical noise from complicated linkages, steam hissing from various valves, injectors, pumps and exhaust blasts, No. 4014 made quite a racket. It was stereotypical “steam train” noise, louder.

It had a computer in the cab.

Running Gear

Above, three of the right rear driven wheels and running gear. The wheels are counterbalanced individually. While reading up on the 2015 refurbishment of No. 4014, I read that the wheels got sent to a foundry for cleanup and installing new “tires”. These are original wheels, although they look quite new.

The Big Boy class of locomotives was designed for 80 mph, and has 68 inch diameter wheels.

The driving wheels have a circumference of 213.62 inches. At 80 miles per hour (1408 inches per second), the wheels are rotating at 6.6 revolutions per second (38.96 radians per second). That means that the coupling rods make a complete back-and-forth cycle 6.6 times per second.

The counterbalancing of the wheels was apparently placed to avoid any forward-and-backward vibrations from the coupling rods and pushrods. There’s an up-and-down component of the running gear motion, as well. that causes something called hammer blow because you can’t counterbalance for both forward-and-backward oscillating motion at the same time there’s up-and-down oscillating motion.

There’s been a lot of advancement in doing rotations since the beginning of the Space Age - gyroscopes, reaction wheels, jet engine turbine shafts, rotational stability has been much more important than in the past. I bet that modern engineers could do a better job of reducing forward-and-backward vibration and hammer blow than in 1940-41 when the Big Boys were designed.

Valve Gear

Here’s the right front cylinder and valve gear:

I’m beginning to think that the 1880 Railroad in South Dakota is an aberration. This mechanism is clean.

Big Boy pistons are 23.75 inches in diameter. The design boiler pressure is 300 psi. That make the pushrod carry about 133,000 pounds of compression or tension.

If you look at the expansion link support on the right front valve gear above, you’ll see a chain mechanism.

Above, a close up, showing the adjustment knob. My guess is that this is some kind of fine tuning, so that front and rear valve gears work on the same intervals. I could be incredibly wrong on this one.

The large pipe right under the running board is the steam pipe. There’s a upside down goose neck with a different texture. On the forward end of the goose neck is some kind of swivel connection. The front cylinder is on a different piece of the frame than the boiler sits on. The swivel connection accounts for the small rotation of the front frame relative to the rear frame.

Valve Gear Comparison

The 1880 Railroad’s No. 110 valve gear is somewhat different than No. 4014.

1880 Train’s No. 110 right front valve gear above, No. 4014’s right rear below. I could not get a good straight on shot of No. 4014’s valve gear due to the crowds.

I marked the common parts of the Walschaerts valve gear on the above image of both locomotives with the same color.

• Red - expansion link
• Green - lifting link, No. 4014’s is steam piston augmented
• Purple - eccentric rod
• Orange - radius bar
• Yellow - union link
• Blue - combination lever

Union Pacific apparently did a lot of inspection and testing during restoration. The did ultrasonic inspection, and hydrostatic tests of the boiler. The article on No. 4014’s frame didn’t mention any testing with modern techniques, but they had to have tested the cylinders somehow.

Note No. 4014 only has a single crosshead guide, and it’s a forging. The crosshead guides were replaced with new forgings during restoration

Pacing videos and a weird phenomenon

There are a large number of videos on YouTube featuring No. 4014. I’d like to point out something interesting about them.

Here’s a drone pacing it into Greeley on October 23, 2024. If you watch carefully from about 40 seconds to 50 seconds, you can see that the forward and rear valve gear is in synch, or very nearly so.

Here’s a longish video from someone in a car going north on highway US 85 out of Greeley, on the same day. I think the car I was in that day was right behind this pacing car for a while. At about 32 seconds, you can see that the front and rear valve gear is out of synch. Coming to a stop, then starting going at the 10th Street crossing in Greeley has gotten the front and back valve gear out of synch. Some wheels must have slipped or something. By about 12:15 into the longish video, the valve gear is back in synch. You can see a similar thing take place with metronomes. There’s enough play in the mechanisms, or slip or creep (railway kind, not the visco-elastic kind) of the wheels, to allow the pairs of valve gear to get themselves in synch. No. 4014’s cast iron frame must transfer enough energy to encourage this synchronization, and that energy has to be transferred through the articulation. Apparently this sort of synchronization has been observed for a long time, Christian Huygens wrote about it in 1665. and it’s still an area of active research.