In pursuit of "oiled eel" running.
You know it when you see it. The silky-smooth rolling of drivers and rods, without any hesitation or binding. It can be elusive to capture. I thought it worth a try. After all, this Forney has only four drivers!
The Forney parts though, had another tale to tell. For one thing, some driver springs seemed softer than others. Some drivers had more up and down play in them than the others. In carefully measuring the frame with the loco's weight upon it, it leaned to one side as well.
The culprit was uneven spring seats in the frame. Also, the main pin end of both side rods were egg-shaped, as seen here. They had been filed by a previous owner to eliminate binding but that only made it worse!
And, as you can see, the driver springs had varying lengths. Making the spring seats the same for all four drivers and installing new springs would keep the drivers level, with equal contact on the rails.
Here, the Vernier caliper is used to measure the spring seat depth to make sure all four spring seat depths are equal. The deepest cut seat became the measure for all the others, which were cut back with files.
The side rod's main pin end holes were repaired by inserting brass bushings into the egg-shaped holes, to restore them to roundness and above all, accurate spacing. Some brass tubing wall was thinned with a Dremel and cut off disc, slowly rolling an end of the tubing on the disc as it spun. The tubing was reamed to clear the rod pin screw shank. The egg-shaped hole in the rod was enlarged slightly so that the new bushing would be centered in it correctly.
To center the new bushings, measurements were taken from the frame with a Vernier caliper. The forward sides of the journal bearing slots were measured on each side of the frame. They were equal. That measurement would also be correct spacing for the driver pins. It was transferred to the side rod holes, using the inside face of both holes toward the forward end, as that hole had very little wear. Both side rod bushings were fitted to the same exact measurement.
On reassembly, the drivers and rods rolled effortlessly back and forth, up to one point of a very slight bind. It took a lot of patient examination to locate the problem. Turns out, it was one of the crosshead piston rods, becoming tight as it reached the end of its travel into the cylinder.
More about that later. In solving that 'tiny' issue, it turned into a bigger job than I planned!