We have just completed two new main rods, and a new piston rod, as well as modifications to one piston, and repairs to one combination lever for the Western Maryland #734.
The original main rods for #734 were of the strap and split brass big end style, which had been modified into a floating bushing big end style by bolting new big ends onto the rods. One of these new big ends broke several years ago resulting in serious damage to the machinery on that side. The engine has been running since then with parts on loan from the Illinois Railroad Museum.
Dan Pluta from the Western Maryland contacted us last year to see about repair or replacement of the damaged parts so those borrowed from Illinois could be returned. Stress analysis revealed that the area where the new big end broke was a weak design, and exceeded the stress limits covered in the Baldwin Standard Practice, breaking right where Baldwin said it would.
We agreed that new rods of one piece design would be the surest route to avoiding another failure. In order to ovoid disturbing the counterbalance of the engine, Dan specified that the new rods have the same weight and center of gravity as the old ones. Since one piece rods are more efficient than built up rods, this meant that we had to add about 200 pounds of steel to the basic design in order to make these weigh as much as the old ones, about 1100 pounds each. We use a CAD program in design work, which can forecast the weight of any odd shaped part to within 0.5%. We used a big end design in the 1930 Locomotive Cyclopedia as a basis for the new big end design, with the extra metal around the grease fitting adding needed weight.
They measure 141" long x 18" tall x 5" thick. 1045 steel was specified, and delivered by the steel supplier already annealed, and ultrasonically tested for internal flaws.
There is a machine shop nearby equipped with a CNC mill large enough to machine the entire length of these rods in one setup. We contacted them, and they quoted a reasonable price, completing the machine work in about one month.
Back at Strasburg, we drilled the holes for the grease fittings, and pressed in the iron outer bushings for the big ends. We made a new piston rod (the old one was bent), with some modifications in the crosshead and piston fits, where calculations had shown some weakness in the old design. A new piston rod key was also made. We then modified the old piston to WMSR specs for a different design of piston rings, and mounted it on the new rod.
See more pics at http://www.strasburgrailroad.com/wmsr/
Strasburg Rail Road
kelly@strasburgrailroad.com