This might just be the coolest tool I've seen. http://www.rollingrails.co.uk/ Any one have one, or know of other such things? Do they work?
They appear to be well made. My only reservation would be the length of 143mm being too short for a lot of U.S. steam locos, the wheelbase of a GS4 for example is about 190mm. They should be ok for diesels though.
I have a similar product consisting of four independent sets of rollers that one can move to whatever position along the track. I can't remember the brand, but the same company also makes them in HO scale.
A Canadian company called Bachrus makes roller sets called running stands or saddles and they allso make a longer bar shaped device called a stirrup that is made to hold the tenders of steam locomotives. They are handy because they can be placed on an existing track section or just on a plain piece of track. Just apply power to the rails and the locomotives run on double ball bearing rollers. On top of that, they also make a speedometer sensor built into a running stands. It can hook uo to the PC using DecoderPro or that also have a handheld unit. Makes speed matching DCC locomotives a breeze! But without the speedometer, the running stands and stirrups can be used to run locomotives for testing and break in.