Operates on what Radius???

The manufacture's design of the loco....

Had a similar thing happen to me. Bought my 2-4-2 lionchief scout set, supposedly O-27 compatible, nope O-31 and really O-36. the minimum radius is determined by how flexible the engine is. Flangless wheels, removed under cab detail, the slight side to side movement of wheels, how trucks are mounted, how the engine is attached to its tender/calf/cabless/B unit, wheel spacing, how many wheels are coupled as a unit all determine minimum curve it can negotiate. 

No.  I have purchased many locos and found they operate on tighter curves - a steamer advertised for O-54 might run fine through 48" curves, etc., but I have never found an engine that is advertised for, say, O-36 curves that won't go through O-36 curves.  

Caveats:

- curved sections of switches are sometimes a problem, even at the advertised diameter.  My Legacy Mohawl will make it around my O-48 curves but not through O-48 switches curves - fortunatley no problem since I switched them to O-60s.  I have heard of some O-36 steamers that have problems with Fastrack O-36 switches but I can't remember which . . 

- I have two H-7s and one of them really doesn't like O-72 switches unless the front pilot truck is fiddled with just so . . . I've learned how to fuss it into behaving, but i can't explain how . . . it just sometimes binds but I can tell when its on the track so it won't, somehow

No.

Lee,

You may have a good point there. I may try to run this beauty on the 0-48 to see what happens?

What determines the operating radius? The closeness of the drive wheels and trucks or something else?

With my new Legacy ES44, it is the couplers/pilot.  The locomotive by itself with take 0-48 curves, but the couplers will not make the turn if connected to another car. The locomotive minimum  is stated as 0-54.

No, since I have smaller than O-72 curves (O-63 & O-54) I watch that pretty close before making any purchases. May slip up someday, but haven't yet.

Don't confuse radius with diameter.  O-36 is 18in radius.

My 3rd Rail N&W 2300 supposedly will operate on 054. Mine really doesn't do well even on 072. It is fine on 080 and above.

Gilly 

I have engines that run on smaller curves than advertised but never had any that required larger than advertised. That said, be careful with "S" curves. If you have a right hand curve or switch closely followed by a left hand curve or switch an engine rated to run on the radius of the curves might not be able to handle the "S" Curve.

I should add with my scout engine, what happened is Lionel could not agree with itself on the radius, the online store and paper catalog were correct saying O-31 while the website at the time was wrong in saying O-27 was the minimum. Not sure how that happened. Even with highly spaced, broken up with straights between each piece, O-27 curves it derailed constantly. Admittedly a little more complicated than the first question, and something I hope does not happen again. Regardless I hope someone from Lionel hears and fixes it and the online hobby shop stores too.

Lee Willis,

   For the most part I agreed with your findings, until I ran across my new Legacy Shay Engine, that is rated for 036 curves, the coupler is actually to short, once a normal consist is being pulled to allow passage thru 036 curves.  The funny thing is the Shay Engine all alone, will negotiate the 036 curves.  I had to alter the back stairs, uprights on the Legacy Shay, to accommodate the pulling of the consist thru the 036 FasTrack curves.  The new Legacy Shay Engine with full consist runs thru the 036 curves and 036 FT switches just fine now.  Somebody at Lionel goofed on this one, as they did with the 036 rating on the original K-line Shay Engine.

PCRR/Dave

Neat subject. With my 036's I've learned to go by 15 inches max engine length with diesel's. A Williams FM Trainmaster my say 031 but at 17 inches long it looks and runs poorly on my layout where all curves are 036. With steam engines I have always suspected that it has to do with drive wheel size. When I look at MTH Premier and Lionel Legacy steam I rarely see anything less than 054. Just as well I guess, they are very expensive.

I wrote to Lionel about their heavy mikado in the 2015 catalog. It states 36 radius but Lionel admitted that was an error. It should be 54 radius.

With steam engines I have always suspected that it has to do with drive wheel size.

and spacing.

I ran into this problem, too, plus my Shay had a bad right side driveshaft.  It would pull some cars on 36 though, at least mine would, , if the couplers on those cars were cooperative enough.  It seems particularly to have no problem with RMT stuff.  

But there is a fix for the coupler - two actually: one involved a saw and quick and one involving some additonal parts that Elliot Scher went over sometime back.  I made a copy, sort of, of the parts he posted and fixed mine.  The new driveshaft was more problematical but i got mine to work okay on 36.   Not my favorite loco though.