Have you ever wondered why the W-irons on model 4-wheels wagons never end up quite right? They always seem to have to be bent in or out to make the wheels fit properly.
It turns out there is a "standard" for W-irons and bearings documented in the UK around 1982, but most of the manufacturers don't seem to adhere to the standard.
26 mm axles (also NMRA standard)
24 mm width inside W-irons
1 mm deep holes in bearings.
|UK "standard" measurements (from CLAG website)|
The readily available W-irons from Railwest are available in 2 styles:
|"Closed" and "Open" W-irons by D&S (UK)|
The "Open" W-irons (labelled "DS520") are 24 mm inside when folded.
The "Closed" W-irons (also by D&S but not branded) are 23.3 mm inside when folded.
At various times, Railwest has also supplied two different styles of brass bearings. The depth of the conical holes in the different types is approx. 1.15 mm deep vs.1.36 mm deep (averaged over measurements of 5 bearings of each type).
The CLAG website specifically mentions Markits bearings as being "different" with a depth of 1.375 mm - so the deeper bearings probably are genuine Markits ones. The shallower bearings are most likely from North Yard in New Zealand. (Railwest has advised that they will mostly selling the Markits bearings in the future.)
The various combinations possible between the W-irons and bearings are as follows:
DS Closed W-irons, North Yard (shallow) bearings: 25.6 mm between pinpoints
DS Closed W-irons, Markits (deep) bearings: 26.0 mm between pinpoints
DS Open W-irons, North Yard (shallow) bearings: 26.3 mm between pinpoints
DS Open W-irons, Markits (deep) bearings: 26.7 mm between pinpoints
Despite neither conforming to the supposed UK "standard" the combination of DS Closed W-irons and Markits bearings perfectly suits 26 mm axles and the W-irons end up being nicely vertical.
The only downside is that, due to the deeper bearings, the W-irons have to be sprung out further to insert the wheelset. (This issue can be alleviated by grinding or filing a groove in the bearing as explained in the CLAG website. The groove need only be in the bottom half of the bearing.)
The combination of open W-irons and North Yard bearings sort of works provided the W-irons are bent in a bit, and the closed W-irons with the North Yard bearings sort of works but the W-irons have to be bent out a bit.
The combination of open W-irons and Markits bearings is not recommended as the W-irons would have to be bent in quite a bit to suit a 26 mm axles.