Way back in 1993 an “Extra Issue” was published of The OO Road where Bill Johann focused on diesel conversions from HO. What got him started was

… I decided to research Athearn’s products with a view toward chopping, cutting, piecing and scratchbuilding Irv’s hood locos, which had perfect OO hood width (6’), so as to make close to scale OO locos — the “good enough” philosophy. The trucks would have to be widened to match the OO track gauge.

The most straightforward model to rebuild from this article with a “good enough” focus is the 1965 EMD SD40 prototypes (also referred to by railfans as the SD40X) number 434A through F (a prototype photo may be found here; these nine engines were all were sold and did see revenue service for many years — noting however that the SD40X designation also can refer to a very different locomotive that was the test bed for the SD50). The basis of the conversion would be a vintage Athearn SD45 hood, as the first four of these SD40 prototypes had flared radiators as seen on a SD45 with fans in the same configuration and size as seen on the vintage HO shell.

Johann in the article noted that Dave Sacks had taken a simple approach to this general conversion by modifying the trucks and running them in OO more or less as is. Two of those models actually made it to me but in pretty sad shape (seen here), drives completely shot. He had fun running them I am sure but they visually were pretty unsuccessful I feel.

The main wrong detail as those models came to me was the too small (HO) cab. Of course, regular readers know I just had two of these very cabs 3D printed for OO. I had been working on converting these two engines off and on for some years now actually, but was totally stalled by the cab. But not now!

Which brings us to these three photos seen here. What you see is the basics of the conversion, with each photo also showing the comparison of this model to a stock, modern Athearn HO SD40. Big picture, this model will certainly have the heft and look of being a full scale 1/76 model when done, just don’t look at the fine details too close. A recent production Athearn loco is the donor for the drive, which has already been modified for 19mm gauge operation (and much more easily than the old style drives Johann was working with). The frame portion of the original body was widened to match the width of the cab, and the long hood is from one of the Sacks models but raised to match again the height of the cab. From the top and front you can see it clearly is a 1/76 model, the HO roots are not obvious.

The conversion should go pretty quickly from here, reusing the original hand rails and adding other HO details. I will be making a pair of these (#2 will be built on a shorter frame, closer matching the prototypes) and also a GE locomotive for which I also now have a 3D printed cab and an overwide Athearn GE body to mate it with. It will be more or less a GE U23B when done, planned as of now as a dummy rather than powered model, and likely on EMD trucks, as some of these were built with them. None of the three modern diesels will be really accurate models, of course, but I will make them as close as practical to correct and believe they will meet the standard of “good enough.”

Going back to the original Johann article on the conversion, he suggests doing the SD40 prototype or the U23 conversions first (they would be the easiest to complete), and the H16-66 conversion later. Actually I already did that one (see here) which helps me with confidence for the process as well. Johann states he has converted a total of 14 HO diesels to use in American OO, including building SD28 and SD35 models that required extensive body work. Another model he does not note in the article that would be a good candidate is the EMD SDL39, which would be the best conversion of all really as it uses six wheel trucks that are actually of a shorter wheelbase than the standard EMD truck — HO trucks being about right! Maybe someday I will come back and try that, but for now we have these underway, should be some real progress on them by summer.

Continue to Part II of series