Would someone please explain the advantage of boxpok drivers over the conventional spoked drivers? I read somewhere that boxpok drivers were generally lighter than conventional drivers but they hardly looked it. Also, I've noticed some locomotives had a mixture of both boxpok and conventional drivers. What advantage would this offer?Thanks.

The primary advantages of disc driving wheels is more room for ballancing weight and reducing cracking of the driver hubs. Older locomotives sometimes had some or all of their wheels replaced for these same reasons. Often the main driver was the only wheel replaced because it required more weight to ballance and was subject to more cracking due to the additional stresses. This was especially true for heavy, low drivered locomotives that were hard on track and placed high stresses on the driver wheel centers. Passenger locomotives could also benefit from the newer drivers. New lightweight rods were often added to the locomotives at the same time.John Bohon

Why did N&W give them a pass? Why didthey not apply lightweight rods to the Y class?

If you ever get a close-up look at the 1218 or the 611, you'll see that the drivers do incorporate something similar to Boxpok reinforcement on the side of the driver adjacent to the crankpin. I've noticed that some artwork omits this feature, but close up photos clearly show it. The main reason the N&W wouldn't have used Boxpok drivers is they were a proprietary design and the N&W would have had to bought them or paid royalty fees to make them themselves. No doubt the N&W's engineering staff came up with their own improved version of spoked drivers which they felt were more than adequate for their needs.As to your other question, the Y's appear to have had relatively light weight rods although not of high-strength alloy material like the J's as far as I know. The engines were well-enough balanced to be able to run 50 MPH, which is moving pretty well for an engine with 58 inch drivers.

The engines were well-enough balanced to be able to run 50 MPH, which is moving pretty well for an engine with 58 inch drivers...not to mention those massive pistons on the front engine!

The engines were well-enough balanced to be able to run 50 MPH, which is moving pretty well for an engine with 58 inch drivers...not to mention those massive pistons on the front engine!

N&W was an early user of lightweight rods. The lightweight, rollerbearing rods on the J class is the oldest application of such rods on an entire class of locomotives I can think of. I would be very suprised if the Y class locomotives built or substancially rebuilt after the mid thirties did not have lightweight rods. The Y class ran to fast not to be resonably well ballanced with such low drivers. I am sure N&W put all they had learned into the late model ones.John Bohon