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.
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.
Still serving! Built in July of 1944, this Cat D3400 diesel has been aboard the SS Red Oak Victory since the ship was commissioned and currently has 683 hours on the clock. This generator set differs significantly from the 34-15 AC (Alternating Current) units Caterpillar built in-house. DC power was required for marine operation, so Fabick Brothers Equipment Company in Sikeston, Missouri, took specially built D3400 engines and added the Ideal Electric 15KW DC generator heads and the other gear needed for a shipboard installation. This D3400 carries an “SP” suffix in its serial number, indicating Special Parts included by Cat. Those include a water-cooled exhaust, dual oil filters, electric start, a higher rated rpm (1,440 vs. 1,200) and a higher 31.5hp rating. The silver paint was applied at Fabick, OD green being its original color.
Placement of the backup generator varied among the Victory ships, of which there were four common subtypes. It was always in the superstructure above the hull for a good reason; it was well out of the way in case of major damage in the engine room or hull flooding. Power could be maintained even as the ship was sinking. On the Red Oak Victory, the backup generator was placed on the boat deck (second up from the main deck) of the superstructure. The cover behind the “Oak” on the sign is the radiator outlet, which would be opened when the engine was running. Alan Burns, a retired naval officer and now a volunteer aboard Red Oak Victory, stands by after allowing Diesel World access to the generator. The backup generator compartment isn’t part of the normal tour but the tour guides can show it to you by special arrangement.
Unlike most of the land-based generator sets and power units that used a 2-cylinder gas pony engine to start, this version is electric start. It is cooled via a radiator with a blow-thru fan that pushes air out from the compartment. The radiator shell also incorporates a very large oil cooler. Cat built its own injection pump and injectors that popped at 1,750 psi. The daytank above the engine holds about 100 gallons and with the engine burning 3.3 gpm at a full load, that’s about 30 hours of run time to a dry tank.
Much of the small compartment is taken up by a power distribution panel. This is old-school stuff but the unit still works as designed and when main power from the ship’s two 300 KW steam turbo-generators drops off, the old Cat will automatically fire up and take the load within 20 seconds. It cannot take the ship’s entire electrical load, but it feeds the most vital equipment. This includes emergency lighting, communications, gyro compass, certain pumps in the engine room, the electric anchor windlasses, and a capstan located on the stern.
This is a place all Cat fans should visit! As Caterpillar’s smallest diesel, the D3400 is an important part of heritage display at the Doug Oberhelman Visitor’s Center at Cat’s Peoria, Illinois, headquarters. Shown here is a restored 34-15 generator that’s a part of the exhibit. It was restored by Kent Bates, a retired Engineer from the Caterpillar Engine Division. Bates had a 35-year history with Caterpillar and has a passion for the company’s old gear. This unit was built in 1947, the last year of production for the D3400 and the 34-15 generator. Reportedly, it was the backup generator for an Illinois hospital. Yellow paint is the “tell” for a power unit built after WWII. During the war, all Cat equipment was painted military Olive Drab, even the small amount of stuff built for civilian use.
This is a 1941 Cat D3400 power unit and you can clearly see the two-cylinder, 10hp gasoline pony engine mounted over the bellhousing and geared to the flywheel via a clutch. The pony engine could be manually started with a rope or, as shown, with a 6-volt starter/generator. Restored by Kent Bates, it’s now on display at Caterpillar’s engine plant in Peterborough, England. The history of this unit is unclear but it came from Michigan and was possibly used at a municipal water plant. You will be wondering about the gray paint versus the yellow in the other image. Though the tractors were yellow after 1931, Cat painted its industrial engines gray prior to World War II. After the war, everything got the signature Cat Hi-way Yellow.