VINTAGE SMOKE
THE DIMINUTIVE CATERPILLAR D3400
The Caterpillar Tractor Company wasn’t the first American engine maker to offer a diesel, but their engines set an industry mark for power, economy and practicality. Caterpillar was the first in America to apply diesel power to a production tractor in the form of the legendary 1931 Cat 60. It’s not a stretch to say Cat’s D9900 diesel quickly powered Caterpillar to a leading position in engine manufacturing and the Cat 60 did the same thing for their crawler line.
Before those first D9900s were brokenin, the father of Cat’s diesels, Art Rosen, had the design teams working on new diesels for an expanded line of crawler tractors. That new line eventually included the 1938 D2, Cat’s first small diesel tractor. The D3400 diesel was developed especially for it, along with the 3400G gasoline derivative, and both were also installed into the 212 motor grader. The D3400 goes down in history as the smallest diesel engine Caterpillar has ever mass-produced.
Starting in March of 1939, industrial power units with the D3400 were introduced, as well as a marine propulsion version. At nearly the same time, Cat added it to their generator line as the 34-15 Diesel Electric Set, sold in relatively large numbers into 1947. With the engine running at 1,200 rpm (making 25 hp and 128 lb-ft), it produced 15 KW (kilowatts) polyphase or 13 KW single phase, both at 60 cycles. Mounted on a skid and weighing 3,030 pounds, it was portable and versatile. Properly serviced 34-15 gensets could, and did, run for decades without major work.
The D3400 engine was a wet-sleeve, indirect-injected, four-cylinder diesel displacing 221 cubic inches from a 3.75-inch bore and a 5-inch stroke. The crankshaft was supported by five main bearings and the highest no-load rating listed was 1,525 rpm, with a peak power
rating of 35 hp at 1,500 rpm. Those higher rpm intermittent ratings were seen on the D2 crawler and 212 grader or the marine propulsion engines. Generator continuous ratings ranged from 25 to 31.5 hp from 1,200 to 1,440 rpm.
The Cat D3400 Goes to War
The war dominated American industry through the first half of the 1940s and, of course, the D2 crawler and 212 grader joined up and went to war wearing OD paint. So did the 34-15 generator sets and many other Cat products. Less known are the Cat D3400 engines that went to the Navy and Merchant Marine for installation into ships as backup generators. We discovered a Cat D3400 aboard the SS Red Oak Victory (see sidebar), a World War II cargo ship that
served both the U.S. Navy and the Merchant Marine. It’s original to the ship and drives a 15 KW, 240-volt DC (Direct Current) generator that was, and still is, used as backup power.
Cat Evolution
The D3400 engine was produced from 1938 into 1947, with 19,161 built for the D2 tractor, 1,797 for the 212 grader, 6,047 for generators and power units, and 216 as marine propulsion units. Additionally, 2,492 3400G gasoline engines were produced from 1938-42 and were among the last gas engines Cat built. Starting in 1947, the D311 series engines (251ci), replaced the D3400 and became Cat’s smallest diesel. The D311 had dimensions and architecture similar to the D3400, but a larger bore, a crossflow head and more power (57 hp @ 2,000 rpm).
By the end of the 1930s more than a third of Caterpillar’s income came from diesel engine sales and it just went up from there. Postwar, Caterpillar increased its line engine offerings and is still a leading manufacturer of diesels known worldwide.