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Classic Diesels

Size and Scale is a matter of precedent, not planning

Diesel locomotive sizes within O Gauge do not necessarily correspond to the car sizes.  The standard diesels are a matter of precedents set by Lionel and Marx in the 1950s.  While most Lionel diesels were 1/48, some were smaller.  They were about 1/64, or at least "semi-scale."  Marx produced only 1/64 models - in other words, O27.  Other makers' diesels match the 1/64 standard, but higher O trucks make a difference in profile.

Among the anomalies is the Lionel F unit and Alco FA.  The classic F3 or F7 is 1/48, while the Alco FA is a wide 1/64 model.  in real life, they are the same size, but in O a different precedent rules.  K-line has followed it with its own F and Alco units.  Another oddity is that K-line bills both the Alco and its MP15 switcher as O27, though the Alco is 1/64 and the MP15 is 1/48.  We must be aware of the little issues in order to better employ motive power for appearance as well as increased action.

The rationale behind the 1/48 diesels is that they are all models of types that, when scaled down, easily handle 31-inch curves.  A 1/48 F has no problem with O31 or even O27 track.  The 1/64 E7 is another story, as a 1/48 model could not handle the 31' curves easily.  Semi-scale Alcos and F3s are a convenience originally devised as motive power for smaller, cheaper O27 sets.  

Note how some semi-scale locomotives have a lower profile but similar width to 1/48 models.  It makes a difference, especially when running passenger cars.

The classic F3, F7, GP7 / 9 / 38, FM Trainmaster and NW2 are 1/48, while the classic Alco FA is 1/64.  Steam locomotives tend to run between 1/64 and 1/55.

Front view of (l to r) O27 Marx E7, O27 Railking F3, O Scale K-Line F7 and Semi-scale K-Line Alco	Marx O27 E7 has lower profile than semi-scale FA
Classic F unit is significantly linger than semi-scale F3	Marx O26 E7 is not as tall as semi-scale F3
Classic F7 with semi-scale F3	Classic F7 with Marx O27 (1/64 over O) E7.  In real life, E7 is about 20' longer than an F unit.
Scale F7 with semi-scale FA.  In real life, both are the same height and length.	Marx O27 (1/64 over O) S3 switcher with K-Line 1/48 MP15.  In real life, bot hare comparably sized

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