One of the challenges we have faced with the driving wheels (the three sets of large wheels that the rods connect to), is the replacement of the crankpins.
Beginning next week, new crankpins will be machined of hardened steel, and then inserted by a process of freezing in liquid nitrogen (to shrink the steel to allow it to be inserted into the hole).
The center driving wheels have a very old, repaired crack. Since the general offices for the Sierra Railway/Railroad burned twice during its history, we do not have any documentation to indicate when the previous repairs were made.
The old repair has held up well. However, the repair was only made on one side of the wheel. We had some concerns that the stress of the crankpin insertion process could result in further damages, destruction of the historic fabric, and the very expensive proposition of casting new wheels.
So, the decision was made to repair the other side of the crack prior to crankpin insertion. We’ll detail that proces in the next entry.