THE ELUSIVE GENERAL MOTORS 1-71 GENERATOR
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!
THE LEGENDARY 6-71 WOULD SOON EARN A NAME FOR ITSELF IN THE FIRESTORM OF WORLD WAR II.
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.