The worldwide pandemic is causing significant disruption in nearly everyone’s lives throughout the Puget Sound Region, but a core group of dedicated specialists is continuing to work on locomotive 924. They are practicing social distancing, and limiting the number of workers in the shop at once, but still achieving success. Until this week, that meant not more than ten people at a time. However, now the Governor has ordered non-essential workers (and pretty much all volunteers) to stay at home for at least the next two weeks. So this seems like a great opportunity to reflect on and highlight recent progress, and what all the public donations have supported.
Packing – Mechanical packing seals the gap around the piston rod where it penetrates the steam cylinder. The packing has to be installed before the rod is inserted into the cross head. So Jay was busy assembling this puzzle on a Saturday morning earlier this month as everyone else was preparing to install the rods. There is more to this than meets the eye – the packing gland has to be able to resist 185 lbs of saturated steam without leaking.
Radius rods – Meanwhile, Paul and Larry were cleaning up the radius rods for the valve gear, which with Stephenson motion are located between the lead and main drivers. It is an awkward place to reach, but the Museum’s Conservation and Restoration Center has pits 60 inches deep, providing ample room to work from below.
Eccentric straps – Over on the work bench, David and Vic were cleaning and preparing the eccentric rods or straps in advance of their reinstallation. These rods fasten around the main driver axle on an eccentric (offset center) and as the axle turns they convert rotary motion into a longitudinal oscillating displacement (back and forth motion) to move valves that control steam entering and exiting the cylinders.
Cross head – After Jay completed tightening of the packing, the piston rods were inserted into the cross heads. The cross head is the assembly that most observers will recognize on a steam locomotive. It is the component that moves back and forth with each rotation of the main driver, and at high speeds might appear to some to be just a blur. The rod has a taper and fits just about perfectly into the cross head – so there is no movement between the two parts. Then a tapered key or keeper fits through the cross head and the end of the piston rod to ensure they remain tightly in position.
Main rod – Installing the main rod is a delicate dance. This forged assembly is – even on a light locomotive such as the 924 – amazingly heavy. Fingers or toes that are in the wrong place will be effortlessly and mercilessly removed. So with the aid of a wheeled hydraulic table to adjust the height and position of the rod, the work was performed with just three workers. The first milestone was installation of the little end into the cross head. It is attached with a pin just behind the piston rod end.
The next step was to raise the big end of the rod into position ahead of the main rod crank pin. This involved another form of dance as the entire cross head, piston and rod assembly was gently moved forth and back until it was in just the right place. And yes, there was a great deal of careful measurement and calculation, too. Otherwise when the bearing brasses were installed and wedges tightened to hold them in place, the rod would be either too long or too short, causing catastrophic failure.
With the rod in the correct position, the bearing brasses, wedge, and a large fitted bolt were applied to hold everything in the correct position. Lyle was careful to apply anti seize coatings on all the components prior to assembly.
The resurrection of Northern Pacific locomotive 924 is continuing to take shape at the Northwest Railway Museum. Support from 4Culture, Washington Heritage Capital , Schwab Fund, Microsoft, Osberg Family Foundation, Boeing, Emery Rail Heritage Trust, more than hundred individual donors, several awesomely skilled employees, and dozens of dedicated volunteers is making this work possible. Additional progress will be described in another article that will appear in early April.
Project 924 continues to welcome your support! To make a donation online, please visit the Northwest Railway Museum donation portal and select “steam locomotive.”
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