2 Rail 3 Rail Minimum Radius Query

The differences would be the blind drivers on a steamer.   Probably (and I am not familiar with MTH/Lionel steamers) there is no difference in the lead truck and trailing truck pivots.   

The talgo coupler mounts on the tender would be different than the more prototypical body mount on the 2 rail.

You CANNOT (generally) run a 3 rail engine on 2 rail track because the drivers are not insulated.    In 2 rail you pick one side of your  current from one side of the loco, and the other polarity from the other side or the tender.    If the loco has uninsulated wheels, you get a dead short.   

Flange size and shape is a different issue.

If you buy the 3 rail engine you can definitely put 2 rail wheels on the engine truck and trailing truck. I do it on all of mine. NWSL 172 tread wheels. However when you go to scale diameter wheels there are sometimes clearance problems. If you use 72 inch radius curves, one may not have a problem. But, it makes the loco present so much better.

Modified 3 rail masterpiece hudson

Thanks for the advice guys, I was half under the understanding that it was a simple flick of the 2rl-3rl switch,but if I have to go buying or modifying one side of drivers and/or pilot/trailing truck axles to insulate them I may give it a miss,unless replacement wheel sets are available out there,I only have MTH engines,8 diesels and 1 steam,

Oh can I buy after market 2 rail drivers or drivers and axle sets for a 2 rail MTH Southern Pacific GS-4?

gbarnewall 

 

Oh can I buy after market 2 rail drivers or drivers and axle sets for a 2 rail MTH Southern Pacific GS-4?

 

I don't understand your question. If you have a 2 rail GS-4 then it would already have 2 rail drivers on it. Why would you need another set? 

If you meant to say that you want 2 rail drivers for 3 rail GS-4 then unfortunately the answer is No they are not available. Believe me I wish they were. Then I could convert 3 rail steamers at much less cost then paying someone to machine new drivers which is very labor intensive. 

To go from 3 rail to 2 rail on a MTH steam locomotive IS as simple as flicking a switch and removing the center rollers. I assume you're wondering if it will handle the curves on your layout? I cannot say for sure that it will but I can say that Mike Pitogo has stated more than once that his MTH Big Boy (which also is rated for 72" radius curves) ran on much sharper curves than what the catalog stated. I may be remembering wrong but I think Mike stated that his Big Boy actually ran on 36" radius curves. Remember it is articulated. I believe it is the MTH 2-10-4 rigid locomotives that require the larger curves. 

prrjim posted:

You CANNOT (generally) run a 3 rail engine on 2 rail track because the drivers are not insulated.    In 2 rail you pick one side of your  current from one side of the loco, and the other polarity from the other side or the tender.    If the loco has uninsulated wheels, you get a dead short.   

 

Jim, in conventional 2 rail vs. 3 rail you are 100% correct but in this case none of this applies when discussing MTH 3/2 locomotives. They are sometimes called 2 rail and 3 rail locomotives but I think it is best to call them either Hi-Rail or Scale Wheels. Both versions can run on either 3 rail or 2 rail track. There is no need to insulate anything. The OP mentioned the Big Boy and the Challenger which both are offered in the 3/2 version. I'm not sure about the FEF. I think that one may be the just regular 3 rail locomotive. 

Obviously, on the Hi-Rail version the flanges are larger and (I have found that 3 rail usually has the flanges closer together and not in compliance with NMRA 2 rail Standards) so the gauge is smaller. The Scale Wheels version has all drivers flanged with typical 2 rail flanges set to NMRA Standards. The Hi-Rail version may not perform well on scale turnouts and the Scale Wheels version will not perform well on tubular track. 

Hudson J1e posted:

gbarnewall 

 

Oh can I buy after market 2 rail drivers or drivers and axle sets for a 2 rail MTH Southern Pacific GS-4?

 

I don't understand your question. If you have a 2 rail GS-4 then it would already have 2 rail drivers on it. Why would you need another set? 

If you meant to say that you want 2 rail drivers for 3 rail GS-4 then unfortunately the answer is No they are not available. Believe me I wish they were. Then I could convert 3 rail steamers at much less cost then paying someone to machine new drivers which is very labor intensive. 

To go from 3 rail to 2 rail on a MTH steam locomotive IS as simple as flicking a switch and removing the center rollers. I assume you're wondering if it will handle the curves on your layout? I cannot say for sure that it will but I can say that Mike Pitogo has stated more than once that his MTH Big Boy (which also is rated for 72" radius curves) ran on much sharper curves than what the catalog stated. I may be remembering wrong but I think Mike stated that his Big Boy actually ran on 36" radius curves. Remember it is articulated. I believe it is the MTH 2-10-4 rigid locomotives that require the larger curves. 

My apologies for the confusion,that was a second thought I was having,my 2 rail GS-4 wont run on my curves(my own fault as I thought I had bigger than 42" radius curves,I do in fact have 40.5" radius curves) so I was just thinking if I could get my hands on the 2nd and 3rd drivers with axles,(if the drivers differ from one another on this engine) I could machine the flanges off making the middle two drivers blind much like a 3 rail engine but in 2 rail form

Thanks for clarifying the 3rail to 2 rail switch,I will bare that in mind for future purchases as for any 2 rail engines which wont run through 40.5" curves I will buy 3 rail.

Thanks again for the help as I'm relatively new to the hobby and there is so much to know/learn

gbarnewall posted:

Thanks for the advice guys, I was half under the understanding that it was a simple flick of the 2rl-3rl switch,but if I have to go buying or modifying one side of drivers and/or pilot/trailing truck axles to insulate them I may give it a miss,unless replacement wheel sets are available out there,I only have MTH engines,8 diesels and 1 steam,

 

Oh can I buy after market 2 rail drivers or drivers and axle sets for a 2 rail MTH Southern Pacific GS-4?

 

Some of the MTH later Premier steam locomotives are designed as 3 rail/2 rail with the flick of the switch.  Instructions are included.  This small decapod is a 3/2.  The left side/right side wheel/axles are isolated/insulated.

One of the tender trucks is set for left side pick-up, the other for right side pick-up. 

Note the insulated axle bearings.  You can also see the left and right wheel isolation.  Note the non-conduction bushing, between the wheel and axle,  second picture.

Steam is tricky because you have several variables involved. In 3-rail (Hi-rail) configuration, every 3-rail steam locomotive built to date will negotiate 36" radius (O-72) successfully because the inner drivers are blind (flangeless) and the pilot wheels tend to be smaller.

in 2-rail configurations, all drivers have flanges which restricts the sharpness of the curves the unit can negotiate. This is further complicated by the typically larger (correctly sized) pilot wheels which may hit the cylinders on sharp curves. That said, SOME MTH scale-wheeled steam locomotives will negotiate 36" radius (O-72) curves. This includes:

• The ATSF 4-6-4 Hudsons (un-shrouded and Blue Goose)
• The Big Boy (go figure on that one and I suspect the Challenger can do it too)
• USRA 0-6-0 and 0-8-0 switchers
• The USRA light Mikado (as I recall)

Needless to say, don't try something like that with a Northern, Mountain, or Texas.

I have several MTH scale-wheeled diesels that I run at the 3-rail club (I have a lot of YouTube video on this). All have the scale wheels in place because I'm too cheap to spend $60 for hi-rail axle sets (besides, I've been hanging around this list too long and it would seem "wrong" to do so). None has derailed on 36" radius (O-72) with cars in tow, but the larger six-axle units (longer truck wheelbase) will find the bad spots on the layout. The ones I have include:

• SD70ACe (SD70M2 applies, too). I have nine of them with scale wheels and have run them all on the layout at one time or another.
• C40-8/C40-8W
• C44-9W
• ES44AC. The GE Evolution Hybrid runs fine along with its test car in tow
• GP35
• GP38-2
• U25B

Make sure your track work is even if you're running MTH scale-wheeled engines on 3-rail track as dips in the running rails will allow the engine to ride on its pickup rollers and derail. As a practical matter, good track work should be done on anything other than a beat up old branch line, but that's another story for another time.

As to rolling stock, there are also a lot of variables, but the 2-rail rolling stock I buy has all worked. The one I thought would be a problem was the 89-foot Atlas trailer flat, but they work fine. You have to be judicious about what you couple longer cars to, though, otherwise the long car will derail the shorter car coupled to it unless you have REALLY big curves.

Hope this helps.

In 3 rail when we talk 072 we are talking a 72 inch circle. In 2 rail 72 inch radius means a 144 inch circle. Huge difference.

Ros Miller

Thanks for the advice and information guys! 

So would I be right in thinking that newer steam locomotives,which are stated to be "Proto 3-2  3-Rail 2-Rail conversion capable" can be simply made to run on a 2 rail layout by a simple flick of the 2rl/3rl switch and removing the pick up rollers?

As for my 2nd problem,created whole heartedly by myself as I tend to do,is there a fix that can be done to my 2 rail GS-4 so it can run on my 40.5" radius curves,does anyone know of replacement blind center drivers available after market? is removing the two center driver/axle sets and machining the flange off an option(albeit an ugly ill-advised fix)?

Just as an example, I have an MTH scale wheel H3 2-8-0 which is a small late 19th century consolidation. It will negotiate 24" radius just fine. In general terms you will find that MTH overstates the minimum requirement for their steam engines. They are able to negotiate tighter curves than most traditional 2 rail engines due to the compromises that are built in to allow them to operate on 3 rail as well.

If you want the middle drivers "blinded" send the model to Joe at Baldwin Forge and Machine. He will take care of it for you. His work is top notch. That should allow a tighter radius operation.

I agree with Jonathan on the MTH minimum radius. It is also sometimes true for Sunset/3rd Rail. I have a Sunset Mohawk that is supposed to be 56" minimum and it can handle an Atlas 49.5" radius. True, not a large difference but when it comes to space every little bit counts. 

GBARNEWALL, if you still are interested in having your drivers cut down to make blind drivers you can contact CSX Al of Millhouse River. He knows a guy who will cut down the extra large flanges of MTH Hi-Rail steam engines so that they run good on regular 2 rail track. I assume he could go a little further and make blind drivers. Well, it can't hurt to ask.