Diesel World - - Contents - Spe­cial thanks to Kent Bates, Greg Blasquez, Alan Burns, Cater­pil­lar Inc., Lee Fos­burgh, Ron Nash and ACMOC.

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.

 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...

 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...

 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...

 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...

 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...

Im­age by Kent Bates

 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...

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