Driving Wheel Repair, Part II

The driving wheels of the Sierra #3 are made of cast iron, and are almost 120 years old.  An old crack in one of the center driving wheels had been repaired, on one side, many years ago, and we had concerns that the un-repaired side may be further damaged by the insertion of the new crankpins. 

Cast Iron is the most difficult of all metals to weld.  Proper cast iron welding requires disassembly, and preheating of the metal.  Furthermore, an unsuccessful weld attempt can actually damage the cast iron, making it brittle. 

For this repair, we chose to work with LOCK-N-STITCH Inc., a cast iron repair company in Turlock.  Their patented cast iron repair system has been used in many different applications, including a repair on the US Capitol Dome in Washington DC, which is also made of cast iron, and is a historical artifact.  So, we knew they would understand our concerns.

Custom-cut steel for repair

Custom-cut steel for repair

Outline of proposed repair on inside of driving wheel.
Outline of proposed repair on inside of driving wheel.
We had the driving wheels transported to their shop, then Curator Lisa Smithson and Railroad Restoration Leadworker George Sapp made a visit to discuss the proposed repair methods.  This was a critical repair, and it was extremely important that we didn’t inadvertently cause further damage.  Aside from our concerns for maintaining the historic integrity of the locomotive, it would also be very expensive to replace the wheel, requiring a model, casting and transport, and would delay the entire project.
The staff at Lock-N-Stitch discuss repairs with George Sapp.

The staff at Lock-N-Stitch discuss repairs with George Sapp.

After discussing the repair process, George and Lisa gave the go-ahead for the work to proceed.  The crack was repaired by the insertion of several precision cut “locks”, pieces of high tensile steel plate that are precision manufactured to fit a precision drilled hole pattern into the side of the wheel.  First, thin locks were inserted into the holes, with a thicker lock “cap” at the surface.  These serve to add strength to the repair and prevent further spreading.  The rest of the crack was stabilized with their patented CASTMASTER stitching pins that have unique threads that actually pull the sides of the crack together and add more strength. The wheel was returned to Jamestown last week, and we’re pleased with the results.

Viola!  Completed repair.

Viola! Completed repair.

Now we’re ready for the new crankpin insertion!

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