ALL IN THEFAMILY

but only 130 on the other due to a blowby problem. The average was 137.195, and it was a record. It beat the other diesel record-seeking car in the group—the Waukesha Silver Comet—by 4 miles per hour.

Growth

From there, the Model H was in production and being used in every venue where a diesel could be found. The automotive applications were few at first, but the H saw widespread use in marine and stationary applications—both areas in which it became a staple.

The 1930s saw a gradual increase of diesel applications in trucks, and the 1932 list included Gotfredson, Indiana, International, Kenworth, Klieber, Linn and Nelson-lemoon. By the late ’30s, the list had grown to include Autocar, Available, Corbitt, Dart, Diamond T, Fageol, FWD, Gramm. Hendrickson, Hug, Mack, Marmon-herrington, Moreland, Oshkosh, Peterbilt, Sterling, Ward La France, Walter and White.

Tweaks

Updates to the Model H started almost immediately, with the first one coming in 1935 by increasing the main crankshaft journal diameters from 3.250 to 4.50 inches. The H and all its progeny would retain that dimension. At that point, the updated engines became the HB models, and the previous engines became the HA models by default. The HA six was commonly rated at 125 hp at 1,800 rpm and 420 lbs-ft at 1,000 rpm. The HA four was rated at 83 hp at 1,800 and 340 lbs-ft at 800 rpm. The HB six jumped to 150 hp/500 lbs-ft, and the four to 100 hp.

Early Cummins engine designations have been the source of some mirth over the years. At the beginning, automotive units were to be called HA, bus versions HB, industrial versions were designated HI and marine versions HM. After the bus deal flopped and updates started, the naming convention changed (as noted in the paragraph above).

Further designations were HBI for industrial offhighway applications, HI for industrials with feet for base-mounting, HIP for an industrial with feet and a radiator, HP for a power unit with an enclosure, radiator and clutch, HM for marine and HGA for a generator set. From there, the cylinder configuration was indicated by a “400” for the four and “600” for the six. This “alphabet soup” would only grow like a fungus over the years to cover all sorts of combinations.

Development for the first big evolution of the H began in 1942, and the first production engines appeared in January 1945. These were dubbed the NH. The upgrade started with four-valve heads, as well as a displacement increase to 743 cubic inches for the NH-600 via a bore increase to 5.125 inches. Much speculation exists about what the “N” signified. Some claim it was for “new,” but old hands interviewed years ago by Lyle Cummins (Clessie Cummins’ son) for his various historical writings about the company indicate there was no established meaning. However, it was generally considered to stand for “new head.” The standard HB engines continued to be produced in the various configurations.

Another upgrade came in 1949 with the advent of the HR, a two-valve “economy” version of the NH. The second 1949 update was the Double-disc (DD) pump, a refinement of the original SD rotary pump. Although the SD had become outdated in many ways, it was as reliable as gravity. The DD became a stumble in Model H history. On the plus side, it was half the size and

 If you wonder what the pumps looked like, here are the four varieties of SD pumps. They were the size and weight of later econo car engines! The “compressor” types were plugged outboard of an air compressor that was driven directly from the accessory gear drive at the front of the engine. The “less-compressor” types were driven directly off the accessory drive.

 When Cummins began adding turbochargers to the line in 1954, NH power outputs jumped to 300 and 335 hp for the automotive applications. By 1958, Cummins engines began being known by their model line and hp (for example, NH-335 for the 335 hp NH).

 The DD pump was more compact and was designed to provide better metering than the SD pump. It met those standards but wasn’t nearly as reliable or adaptable as the SD pump.