Know Your Diesels – The Detroit Diesel Series 71

Welcome to the first in a series of stories relating to famous diesel engines of the past and present.  I can’t think of a better one to start with than the Detroit Diesel Series 71. The story begins back in 1938 when GM subsidary Detroit Diesel unvieled thier first product, the two stroke, inline 6 cylinder 6-71. The inline models were offered in a one, two, three, four and six cylinder variants. In 1957 V-block versions were introduced and would eventually included 6,8,12,16,24 configurations. At first glance the naming convention seems cryptic but is rather straight forward when you think about it. For example, the 6-71. The six stands for the number of cylinders, the 71 stands for the cubic displacement of each cylinder. The 12V71 is a 12 cylinder in a V-block setup. To continue the code a T would stand for turbo charged. L or N would stand for low profile, a setup commonly used in buses. The larger of the 71 series in a V-Block configuration were usually two of the smaller setups married together our used the same set of heads allowing parts to be easily swapped. The applications of the 71 series were limitless. 6V-71 were common with bus and coach builders. 8V-71 were popular with firetruck manufactures, it is pretty difficult to find an old fire truck without an Detroit under the hood or cab. But to really appreciated a Detroit you have to hear it, they truly have a sound all their own. So, on to the videos.

6-71 – 190 HP

12V71 – 450 HP

8V-71 – 318 HP

I hope you enjoyed my novice homage to this great and long lived engine. Despite their unfailing ability to constantly leak oil you will still find fans of the 71 all across the globe. Please feel free to correct or and any relevant information by emailing eric@dailydieseldose.com or just leave a comment below. If you have a candidate for the next KYD story let me know!

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47 Responses to Know Your Diesels – The Detroit Diesel Series 71

  1. Pingback: The Worlds Fastest Truck |

  2. Tim Henshaw says:

    In my mind one of the best engines every made. Not the most powerful, but what other engine has lastest the test of time like this one.

    Love those Rocky Mountain Hummingbirds!

  3. willie kemp says:

    my question,I have a 6v71 lh rotation eng I am a mechanic too and want to change it to rh I know how to do this but am wondering if the cam shafts are the same

    • Rupert Penjab says:

      The cams are different between the lh aha rh versions. If you ever tried to stop one of these engines by stalling it you know they will run in reverse, but the power isn’t right, you have to change the camshaft.

    • Dick Hoover says:

      I was told by a mechanic that the same camshaft was used for either rotation; it had to be removed and turned end for end. Not the same for the starter, you will need one with the correct rotation.

  4. You should be a part of a contest for one of the most useful blogs on the internet.

    I am going to recommend this blog!

  5. Roy Kennedy says:

    Before GM made Detroit Diesels in V configuration, they married two or four 6-71’s together in”twin” or “quad” installations. I remember seeing two quad installations in the engine room of an ex US Navy inshore minesweeper. Imagine the glorious howl of two 24 cylinder powerplants at full throttle. Makes my spine shiver! I worked on boats with 6-71 and 4-71 engines. No matter how many cylinders, they all sounded the same to me, a nice throaty rumble at idling speed that became a uniquely soul stirring scream at 1800 rpm. Wonderful.

    • Rupert Penjab says:

      You certainly did not walk around anywhere near the air intake with an oilers rag in your pocket.

      • Owen F. McCaffrey says:

        I sniped a bunch of LCVPs, Mike6 boats, and Captain’s Gigs as an engineman in the U.S. Navy from 1973-1977. Motor Whale Boats too (Perkins powered). I became really proficient at trouble shooting and rebuilding Jimmies. It was my passion at the time. I used to rebuild and pop test the injectors as well. In addition, I also operated, maintained, and took part in rebuilding one of our Fairbanks-Morse emergency generators aboard USS Coronado LPD-11. Later in life I used to drive a 238 powered White 4000 single axle tractor with a 10 sp. Roadranger pulling tank trailers. Love the Detroit 2 cycle sound! By the way…the are made to run up to 2,100 rpm. Typical operation. Thanks for the memories!

  6. Roy Kennedy says:

    Further to my previous comment, I remember a pair of “handed” Gray Marine 6-71 engines, with Twin Disc marine gearboxes (Allison Division of GM) that had been taken from a landing craft, so they had been built during WW II. They still had their brass plates on the flywheel housing with the official number issued by the US Bureau of Ships. They had the larger injectors, and when the boat was fresh out of refit, they could push her along pretty smartly. We used to run up to 1500 rpm, but could push 1750 if needed. The biggest trouble was keeping the seawater cooling system clear of weed and mud which could cause overheating. The boat was eventually scrapped, but I don’t know if the jimmies survived.

    • Eric says:

      Unless someone was foolish enough to junk them I bet they are still running!

    • Owen F. McCaffrey says:

      That’s so true Roy. As I remember (it was many years ago) you had a sea water strainer before the keel cooler you had to keep clear. The Jabsco pump did not like to run dry. We used to pack the rubber impeller with grease to lubricate them until they picked up salt water. It was just a half-dozen Phillip’s head screws to get the cover off. I would do it again! Sometimes the bosun’s mates would let me drive the boat (Mike 6 or LCVPs) I got pretty good at it! I even landed 80 or so drunk Marines up against the ship. They all were laughing and taunting me. I made a smooth docking. We used to cook misappropriated Marine C-rats on the exhaust manifolds. I even steered an LCVP drive by of a Russian cruiser off Cypress one time! All done with Gray Marines. Good times.

  7. Charles Jarvis says:

    While in the US Navy I was in Viet Nam on lcu boats. There was 6 engines on each boat, three 6-71’s for power; two 2-71’s for electric power and one 4-71 for the anchor winch. The engines just ran and ran. We had injector problems because of dirty fuel, so injectors was replaced frequently. The 6-71’s turned a 4 foot 4 blade prop, engine ran at 1600 rpm’s. A few times ( in time of need ) would be pushed to 1800 rpm’s. One day we blew an engine ( actually the twin disc clutch ), Pieces was every where.
    Always liked the sound of the engines running at cruising speed ( 1600 rpm ). One class of boats had a pair of 6-71 together on one shaft, one right hand rotation and one left hand rotation, I think they was turbo charged units These boats had two shafts. Very dependable engines all the time, as long as the fuel was good and oil was maintained. Charlie J.

    • Owen F. McCaffrey says:

      Thanks for serving Charles! Great story appreciated by this former Navy boat snipe. I sure do remember those twin discs.

  8. Hawse Pipe says:

    I have 12, 8, 6 & 4 V-71 detroits firing both my fleet of tugboats and workboats as well as a few cranes and dredge pumps.

    They are all Naturals and I simply love them. Not much is reliable in this world and at sea I have learned that I can count on only 2 things.

    1.) Without fail the sea will be relentless and when it bears its teeth there is absolutely no room for error or hesitation, particularly in the engine room.
    2.) My Detroits will never stop running and will dig deep to power through anything the sea throws my way. The only reason they will stop running is because I have safely returned to port and shut them down.

  9. Out of the million miles or so I drove 18 wheelers across the lower 48 many years ago, I must have around 400,000 miles in a Freightliner with a 8V71. They were commonly called 318s back then also. That was the horsepower rating with a specific injector size, mine had 290s. The transmission was a two stick 4×4, a Spicer, I think. It was the best designed of the two stick transmissions I had experience with.

    All the Detroit two cycle diesels had what is called a ‘roots blower,’ a mechanically driven supercharger with two spiral, intermeshing, rotating lobed shafts that compress air. They were a basic part of the design and I doubt the motors would run without them.

    Mack engines commonly had turbochargers back then. Later on turbos were paired with aftercoolers and the power really began climbing.

    • jay dee says:

      I own a 1959 GMC 860 short nose cab over hosting a 6-71 DD coupled to a 5&2. I love everything about my truck. He’s a grumbly looking ugly mutt that musters up one hell of a racket anything over idle. Yessir, my truck: all the right parts in all the right places. I love my truck oh yeah!

  10. Brett Hughes says:

    These engines seem to get everywhere. The first time I saw and heard one of these was in 1983 in the technical collage I was attending in England. A yellow 6V-71 with a Roots Blower sat on top. It was on a test bench and I could hardly hear the engine over the sound of the blower.

  11. alex putman says:

    my dad has a tug boat with 2 1983 6L-7 1s and the port one blow up but still run hard to start will run (try that with a cummins) it blow up because the port water pump broke (i think it was made by cummins) i am only 14 and detroits may be befor my time but they are still the best

  12. Rupert Penjab says:

    The Fire truck manufacturers really preferred the 53 series Detroit engines…….. it made for an interchangeable gas/diesel application as the 53 series is a near interchange for a gasoline engine and didn’t require gear ratio modifications.

  13. frank oruene says:

    observe high temperature on a 8v 71 detroit diesel radiator and fan cooling, ive flush radiator but temperature is still high

  14. Chelsey says:

    Hey Everyone!
    I have a question about GM detroit diesel 3-71 marine engine. I am unsure of a couple of things about how to service this engine. I am looking for some helpful knowledge.
    We have change the oil for the marine gear but don’t know where to fill up the oil fo the engine oil….? We have located an oil strainer but arent 100% sure if this is the fill in port? Any help would be much appriciated. There aren’t alot of helpful forums out there so im hoping someone in here can help me out!

    Cheers!

  15. Crabber50 says:

    I have two 6-71TIB’s in my boat and absolutely love them, the more I learn about them the more I love them. Really appreciate all the comments, love to the history. Thanks for your stories and service.

  16. Todd says:

    I have a 671 in my 1955 FLEX VL 100 tour bus. Jake breaks and Alison Transmission. What a blast to drive. I love the sound. I worry if I ever need a mechanic, I will never find one who can work on this old power house. Costa Mesa Cali.

    • Eric says:

      Hopefully that day never comes. The 6-71 has been around for almost ever. Lets hope a few from the next generation learn a thing or two about them.

  17. Tom Christman says:

    The bore and stroke on the 71 series is 4.5″ x 5″. They stopped making the 2 stroke Detroits in 1998 (they still make the 6V-53TI, 8V-71TA and 8V-92TA for military vehicles). It is interesting to note that the 2 strokers were cancelled because of being dirty burning and couldn’t be cleaned up to smog standards.
    Yet the largest and most fuel efficient engine is a 2 stroke made by various companies. The largest has a 39″ bore x 135″ stroke (yes that’s 3″ over 11ft!). They power the big container ships and by cross section, look like big versions of Detroits.

  18. Todd says:

    671
    Does anyone know where to fill the transmission fluid? Theres a canister above the tranny on the very back of the engine.
    Thank you,

  19. Drew Hall says:

    I need your help or that of any diesel mechanic you may happen to know.
    The all-steel 1940 former Baltimore City Police Patrol Boat CHARLES D. GAITHER supports a Detroit 671 diesel engine in her spacious engine room. Can anyone date the engine by its serial number of 6718454. It has a five-pointed star following the number and we were wondering if this signifies it as being original, rebuilt or something entirely different. If it is the original engine, most likely it was manufactured between 1938 and early 1940 just prior to when the vessel was launched. Can anyone possibly give us more information about serial number 6718454 (star) Thanks.

    • Eric says:

      Drew, I would be interested in hearing more about the history of this boat. If you can send in a photo or two along with any interesting details I’ll put together a post that hopefully will be seen by more eyeballs. Email eric@dailydieseldose.com

  20. crazy mike says:

    i have a 83 white road boss with a running 671t in it right now with a hole in the block, no oil in motor or coolant, connecting rod smackin around and starts up in the pa. winters !!!!!! no bs. Awesome engine!!! try that with todays crap.

  21. Andrew King says:

    The most reliable diesel ever built. The best sounding engine is the 6-71 and 8V71
    natural in a truck fully loaded going up a grade. They go a lot better with a turbo and more economical but the sound changes. I want to buy an early 1980’s R600 Mack
    bogie with a slightly extended chassis and stick a 318 or 6V92T in it and a 48 inch sleeper. Rt0 9513 Alcoa wheels on the front. I’m from Brisbane Australia.

  22. Mike says:

    Best diesel for sawmills an some trucks they will run for ever

  23. Adair James says:

    my field service book says Detroit made 568 inline 24 cylinder 71’sne seen one

    • Bill Barsby says:

      I won’t think that there would be an inline 24 cyl. The V16-71 was two V8-71’s bolted end to end so I would the that the 24-71 would be two V12-71’s bolted end to end the same as the V16’s. I have never seen one though I have seen 16-71’s though.

  24. Bill Barsby says:

    Years ago I had a 125kw gen set powered by a V671 . It ran at a constant 1800 rpm. I never leaked a drop of oil and was the only diesel that I have ever seen that the oil was the same colour going in as when it was changed. That oil never got black. They ate great engines.

  25. Kevin Dutchers says:

    Any idea what a 6-71-based design could be pushed to, hp wise, with modern metals, rings, bearings, etc and not worrying about emissions?

  26. Dayne says:

    My company dismantles and parts out old Euclid and Terex off road haul trucks. We still get to play with these engines almost everyday. Such a great sound!!

  27. Al Lindner says:

    I miss the old 2 cycle Detroits, very reliable and parts were inexpensive compared to Cat or Cummins. The ’71 series were great, the ’53 series were junk, also the ‘149 series were excellent as well. Shame they are no longer in production.

  28. Robert Cates says:

    Im looking at a boat with GM 4-71-TI’s with 6000 hours. What What I’ve read is they last a Long time but are they at a point of needing replacement or overhaul. Thanks for any help

  29. bob says:

    Just stripped for planned maintenance, a 6-71 ti marine gen-set after 15000hrs work @ 1500rpm (50hz) mostly under heavy load and still has honing marks inside the cylinders!
    Regular oil changes, run warm but not hot and it’ll just keep going.

  30. tyler green says:

    great stories. I might be able to keep this going. I have a 6-71N in my 44′ commercial vessel, keel cooled. Model:6-71RC7 Serial:6713433 still has original stamp plate. local diesel shops tell me she’s an oldie. Runs like a top, sounds like a jet engine at the exhaust. I am having problems finding a specific manual for this ol’ girl. engine temp got to 190 and overflowed coolant out of the expansion tank. I changed out the coolant, flushed the system as best I could and replaced with fresh coolant. Ran it for approx. 15hrs and she got up to 190 again for about 10 min and back to normal operating temp at 180. Next stop is thermostat but it worries me that the system pushed back pressure through the expansion tank. Any thoughts?

  31. John Russell says:

    At mass maritime they still teach the cadets on in 6-71 s, which is great, my boy just went through the class and will rebuild the 4-71 that sits right behind me in the crane I run every day. The work boat has a 6 -71, and the tugs have 12-71, all naturals getting 25000 hours on the tugs mains before overhaul. They may require some skill to get them to run perfect but this old fool can always make em run, good enough.
    Had to get teir 2 motors in a new machine, lots and lots of wires, no tinkering those babies home when they stop that’s that. When you out on the water……..

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