Some engines have this extra bit on the main rod just ahead of the crosshead. What is the purpose of it? That spot were the rod widens and there is a bolt and washer.

My humble thought is that that device is some manner of a lubricator, perhaps with an oil wick, for lubricating the bottom crosshead bearing . Like I said, just a guess.

Mike

Its a wedge that holds the small end brass bearings in the rod. It can be packed forwards and backwards to efectivly lengthen or shorten the rod when setting the piston clearence.

Thses might help:

That's a very different style, WL. Nothing to do with the rod in question. Nigel's answer is dead-on. The wedge works from inside towards outside, not from top to bottom. The washer-like thing is actually a hollow piece so that the end of the wedge can actually protrude past the surface of the rod into its clearance. The more you pull it towards the outside, the more it shoves the bearing towards the wrist pin end of the rod.

As the split brasses wear, you torque it up to take out lost motion, which also does somewhat lengthen the rod. This isn't critical given the clearance in the cylinder. The wedge adjustment runs out of adjustability before the clearance is lost, preventing a piston knocking out a head. When you do run out of adjustability, you pull the wrist pin, drop the rod and remove the brass; remachine the brass as necessary; shim the forward brass to move it back until the length of the rod between the CLs of the crankpin and wrist pin are the correct distance apart, and reassemble. Then the process starts over again, proving that nothing says job security for a machinist like runnning steam.

I've probably done this a couple dozen times in the wee hours of the morning during firing up.......if you're set up to do it and experienced, it doesn't take long.

dave

looks like wear compensation. Note on sound recordings on some steam engines you hear rod clank, thats worn brass bearings, time for adjustment or replacement.
You want that piston bearing tight-taut or you keep slamming the bearing.

An old master mechanic once told me "It's better to hear them than smell them" in reference to the snugness of rod bearings. Ever hear an N&W Y-6 or A while drifting or one of the EBT's mikes? The operative word is "hear."