The Gen­eral Mo­tors 71 Se­ries two-stroke diesels are iconic and leg­endary mem­bers of the Black Smoke Hall of Fame. They may have done more to bring Amer­ica into the diesel age than any other en­gine. The lin­eage goes all the way back to 1913 and a new diesel en­gine Alexan­der Win­ton and the Win­ton En­gine Com­pany pro­duced for ma­rine ser­vice. GM pur­chased Win­ton in 1930 to fast-track their en­try into diesel en­gine man­u­fac­tur­ing. The Win­ton was an ef­fi­cient two-stroke de­sign but the tech­nol­ogy had only been used in ma­rine and sta­tion­ary ap­pli­ca­tions.

Con­cep­tion of the 71 Se­ries en­gines be­gan in 1934, when GM de­cided to ex­pand the prod­uct line, up­date the Win­ton ideas and im­ple­ment them in a line of smaller diesels to be sold through a new out­fit called the GM Diesel Di­vi­sion (later known as Detroit Diesel). Much of the de­vel­op­ment fo­cused on a new unit in­jec­tor and prod­uct de­vel­op­ment started in a cor­ner of the Cadil­lac plant. By 1937, GM Diesel had the bones of a new en­gine de­sign. By March of 1938, they had the line tooled up, the test­ing done, and pro­duc­tion be­gan in April on two-stroke diesels in one, three, four and six-cylin­der con­fig­u­ra­tions.

Called the 71 Se­ries, the “71” rep­re­sented the cu­bic inch dis­place­ment of one cylin­der (ac­tu­ally 70.93 ci) with a 4.25x5” bore and stroke. The in­di­vid­ual en­gine des­ig­na­tions used the 71 pre­ceded by the num­ber of cylin­ders, so a four-cylin­der 71 Se­ries was called the 4-71, a six was the 6-71, and so on. This be­came the nomen­cla­ture con­ven­tion for the en­tire GM lineup and it con­tin­ued for decades. These en­gines con­tin­ued in main­line pro­duc­tion un­til 1995 and mil­lions are still in ser­vice. They are still in lim­ited pro­duc­tion to­day for cer­tain mil­i­tary mar­kets in which they are the pre­ferred pow­er­plant.

The 71 Se­ries shared many parts and came in a wide va­ri­ety of con­fig­u­ra­tions. To­day we might call it a mod­u­lar de­sign. The first flag­ship en­gine was the 6-71; this leg­endary diesel would soon earn a name for it­self in the firestorm of World War II. It pow­ered ev­ery­thing from gen­er­a­tors to tanks. Marinized by Gray Ma­rine, it pow­ered the ubiq­ui­tous 36-foot Hig­gins LCVP (Land­ing Craft Ve­hi­cle Per­son­nel) onto many hos­tile shores. The 1-71, 2-71, 3-71 and 4-71 weren’t as “front-line” vis­i­ble but were no less im­por­tant to the war ef­fort in their less glam­orous uses. The short-lived 1-71 was the small­est, pro­duced in the least num­bers, and has been al­most lost to time.

The 1-71 came in three known con­fig­u­ra­tions: a gen­er­a­tor model (with a “G” suf­fix, e.g. 1-71G), a power take-off model (“P” suf­fix) and a ma­rine (“M” suf­fix). There might have been a fourth ver­sion built for pumps, but the de­tails have proven elu­sive and the des­ig­na­tion for it is not known. The 1-71 was gen­er­ally rated at 15 con­tin­u­ous horse­power at 1,200 rpm and 87 lb-ft at 800 rpm. It was rated for an in­ter­mit­tent 20 hp at 1,200 and at 25 hp at 1,600 rpm for very brief spurts. In this era, the 71 Se­ries were the so-called low-block en­gines that had a rather frag­ile head gas­ket. Ex­pe­ri­ence has shown the 1-71 doesn’t like rev­o­lu­tions above 1,200 for more than min­utes at a time. At rated con­tin­u­ous power, the 1-71 used about one gal­lon of diesel fuel per hour.

Be­cause it was in pro­duc­tion for such a short time and so few en­gines were built, the pro­duc­tion story on the 1-71 is far from com­plete. The best avail­able in­for­ma­tion states the 1-71 started pro­duc­tion in April of 1938 with the 3-71, 4-71 and 6-71 (the 2-71 came in 1940) but no fi­nal pro­duc­tion date has been found. The best ed­u­cated the­o­ries are that the 1-71 pro­duc­tion ended as early as 1940. It’s known that en­gines were in­stalled later, pos­si­bly from un­sold stock, and the most re­li­able sources list less than 1,000 en­gines built.

The small group of 1-71 col­lec­tors have pooled their in­for­ma­tion and Chris Kouttron has be­gun a 1-71 data­base. Over sev­eral years of col­lect­ing 1-71 in­for­ma­tion and doc­u­ment­ing sur­vivors, he tells us the ear­li­est se­rial num­ber is #8 and high­est is #926. The cur­rent count of known 1-71 sur­vivors world­wide cur­rently stands at 79 units. Fans of the 1-71 have adopted Smok­stak (www.smok­stak.com), a vin­tage en­gine col­lec­tor’s web­site, as a clear­ing house

and gather­ing place. Sources within Detroit Diesel have been con­tacted re­peat­edly over the years for more 1-71 in­for­ma­tion but it’s ei­ther lost or they aren’t will­ing to dig it up from what­ever repos­i­tory in which it might be hid­ing.

The rea­son for dis­con­tin­u­ing the 1-71 is an­other elu­sive fact. Col­lec­tors and his­to­ri­ans spec­u­late that be­cause it was one of many such small en­gines on the mar­ket, and pos­si­bly over­priced in that mar­ket, it didn’t gen­er­ate as much en­thu­si­asm as the rest of the 71 Se­ries. A loom­ing war likely had an in­flu­ence on pro­duc­tion choices. The 2-71 de­buted in 1940 and was pos­si­bly deemed a bet­ter prod­uct to rep­re­sent the bot­tom of the lineup. Dur­ing the war, pro­duc­tion was strictly con­trolled so in­dus­try would de­liver what was needed most for the war ef­fort and the 1-71 might have been con­sid­ered re­dun­dant. Once the war ended, it’s clear the GM Diesel mar­ket­ing team did not see a need to bring the 1-71 back.

In the en­gine col­lect­ing com­mu­nity, the 1-71 is highly prized and in the “Holy Grail” cat­e­gory. It com­bines the ca­chet of a leg­endary line of en­gines with a tiny pro­duc­tion run, with few sur­vivors and great porta­bil­ity. It isn’t a cheap, en­trylevel en­gine col­lectible, and if you have to ask what it costs to join the club, you prob­a­bly can’t af­ford it. On top of that, parts are ex­tremely dif­fi­cult to source. Though some were com­mon to the early 71 Se­ries, the 1-71 had a lot of unique small parts as well and they are vir­tual un­ob­tainium. First­gen­er­a­tion 71 Se­ries parts are dif­fi­cult to find any­way and the more mod­ern parts are not al­ways suit­able re­place­ments or re­quire ma­jor adap­ta­tion to make them work.

As with all 71 Se­ries diesels, tales of longevity are of­ten told. One in­volves a 1-71G that was used at the weather sta­tion on top of Mount Wash­ing­ton, New Hamp­shire (home of the worst win­ter weather in North Amer­ica), from 1939 to 1986 and was al­most never shut down. That en­gine is now in a pri­vate col­lec­tion and is still run­ning. That’s longevity!


Here is a 1-71G, a gen­er­a­tor model, miss­ing its gen­er­a­tor. It’s one of the ear­lier sur­vivors, be­ing the 191st built. The ro­tors in the Roots three-lobe blower are the same di­am­e­ter as all the other 71s in this era but only 2-5/8” long. The GM two-stroke blow­ers can be used on a nat­u­rally as­pi­rated four-stroke en­gine to make boost but on the two-stroke diesel they pro­vide air­flow at very slightly above at­mo­spheric pres­sure.

A com­plete gen­er­a­tor weighed in at 1,480 lbs. A bare en­gine, with­out ra­di­a­tor, tipped the scales at 875 lbs. This one has the cor­rect in­stru­ments, which is rare, but is miss­ing the tach. That tach is one of the un­ob­tainium items that costs thou­sands for a cor­rect re­place­ment. It’s also got the cor­rect pe­riod starter. Miss­ing is the orig­i­nal by­pass oil fil­ter. The gen­er­a­tor ver­sion has a speed ad­just­ment on the con­trol panel for fine tun­ing un­der load.

The bell­hous­ing on the 1-71 was an SAE #1 and the fly­wheel was the heav­i­est in the 71 lineup at over 400 lbs. This was be­cause it was a one-cylin­der en­gine and needed the ad­di­tional weight. A 10 kilo­watt gen­er­a­tor head would have been at­tached here. The gen­er­a­tor ver­sion was by far the most com­mon 1-71 vari­ant and is the most com­mon sur­vivor.

If you are at all fa­mil­iar with the 71 Se­ries GMS, this ex­ploded view will be both fa­mil­iar and un­fa­mil­iar. The 1-71 had a lot of unique parts ver­sus its larger sib­lings but used the same Uni­flow two-stroke prin­ci­ples of op­er­a­tion, with a Roots blower sup­ply­ing air into ports in the cylin­der, a camshaft-driven unit in­jec­tor sup­ply­ing fuel, and an­other camshaft open­ing two ex­haust valves.

Cer­tain 1-71 ap­pli­ca­tions, not this one, fea­tured a hand crank and com­pres­sion re­lease for emer­gency start­ing. That equip­ment is rare, as is an emer­gency shut­off. Ap­par­ently, these fea­tures were found to­gether only on 23 en­gines used as emer­gency gen­er­a­tors on WWII US Navy Pat­ap­sco Class gaso­line tankers, of which 23 were built. An­other sel­dom­seen op­tion was a glow plug sys­tem for cold weather start­ing. Spe­cial types of wicks, called “glow pa­pers,” were lit and in­serted into a re­cep­ta­cle in the head to heat up the com­bus­tion cham­ber. An­other type called “cig­a­rettes” could be in­serted un­lit and ex­po­sure to diesel fuel started a chem­i­cal re­ac­tion that cre­ated heat.

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