Its unmistakable sound was once everywhere, in every city and along every highway in America: the rumbling roar of the Detroit Diesel 6-71 engine. We revisit that wonderful noise with a ride in a beautifully restored 1959 GMC tractor.
Tom Siembieda is the owner and restorer of this 1959 GMC DF 860 semi tractor—a type known to old-school truckers as the “Cannonball” for its nearly round cab and body styling. And under the comically stubby hood of Siembieda’s Cannonball is an original Detroit Diesel 6-71, an engine that makes one of the most recognizable sounds on the road.
A little background on the venerable 6-71 for the uninitiated: First, in the lingo of the Detroit Diesel division of General Motors, the 6 indicates the number of cylinders, while 71 indicates the displacement per cylinder in cubic inches (4.25-in. bore x 5.0-in. stroke). So the displacement here is 426 cubic inches, though versions of the 71 series were made of one to 24 cylinders for every imaginable purpose. In production for decades, the 6-71 model was actually introduced way back in 1938.
Next: Unlike most passenger cars on the road today, the 71 series is a two-stroke design, not a four-stroke. There are no intake valves. Instead, there are simple inlet port openings in each cylinder, fed by a large Roots blower (yes, the same GMC 6-71 blower beloved by drag racers) and two or four conventional exhaust valves for each cylinder. This unique configuration, featuring a power stroke each revolution, gives the Detroit (pronounced DEE-troit by many old-time truckers) its highly distinctive exhaust note: a rattling, rumbling roar. “Screamin’ Jimmys,” the gearjammers called them.
The GM two-stroke design was a highly successful one, too. At one time, nearly all the city buses and a sizable percentage of the over-the-road trucks in America were powered by Jimmys. You could hear them everywhere, from most every street corner. But unfortunately, the same design characteristics that made the engine so popular, and its sound so distinctive, eventually led to its demise. In efficiency and emissions, the Jimmy became hopelessly obsolete compared to modern four-stroke diesels, and the 71 series was finally discontinued altogether in 1995. But fortunately, we have wonderfully restored examples like the gorgeous ’59 Cannonball in this video. Listen to this.
Oh, MCG, how could you? I just can’t contain myself. Make it stop!! Where to begin? 1st, a very nice truck. I can all but guarantee, they didn’t look like this in the ’50’s. These trucks were immortalized by a TV show called, appropriately enough, “Cannonball” ( not to be confused with the hoaky movie “Cannonball Run”) featuring Paul Birch, as “Cannonball Mike Malone” and his co-driver, William Campbell, as Jerry Austin. While the show itself is pretty typical of the era (late ’50’s) it does have some great footage of trucking in a truck just like this ( only a road tractor)
On to the DEE-troit fuel converter ( converts diesel fuel into noise) Yes, they were incredibly popular, mostly because they were easy to rebuild, which was a regular deal with these Detroits, but the I think the 318 hp. 8V-71 was even more popular. These 6 cylinders put out about 238 hp. with “the needle against the pin”, meaning, the only way to keep any momentum up, was to keep the tach at red line. Even dropping a few hundred rpm’s would require a gear change, hence the many gears ( I heard the 10 speed Roadranger was designed just for Detroit’s) And yes, they did “sing a song” , of sorts, but trust me, after about 2 hours of listening to that, it get’s mighty old. If you’ve ever spent any time behind one, as I have, you know what I mean. The 2 cycle Detroit had many jokes made about them, from, slamming your fingers in the door ( to get in the right frame of mind, drive it like you are mad at it), to eat a live frog before starting your trip. They also had a voracious appetite for oil, leaking and out the stack, inherent with any 2 cycle. Still, as said, they were very popular, powering everything from buses to generators at the carnival. ( when I was a kid, we’d go to amusement parks, and everyone would run to the rides, and I would go over to the “generator trailer” and listen to the Detroit diesel screaming away)
I’ve driven many Detroit powered trucks, one more worthless than the next. One dump truck had an air 4×4 transmission ( 16 speeds) and was CONSTANTLY shifting gears. As stated, new regulations for emissions ( I believe they are outlawed in California) along with better 4 cycle diesels, put an end to the 2 cycle Detroit, and I say, thank goodness. And there’s the REAL story on 2 cycle Detroits.
As a followup, the newer Series 60 Detroit ( 6 cylinder, 4 cycle) turned out to be one of the best motors out there, and have been rumored to go 1 million miles before a rebuild. Thanks MCG for bringing up this very important, yet deafening, part of our transportation history, and have a happy holidays to all.
We had them in the Coast Guard :40 ft boats from about 1950 to about 1985, The 40′ footer had 2 twin 6-71’s Spent 2 years with one in Oswego NY. The 30 ft boats had a single 6-71 as it was a single screw boat in contrast to the 40 twin screw.
All I can say is for years before and after me we did one hell’va job with the hull and power! Sound is unmistakable.
6-71’s were popular in commercial fishing boats also.I remember some tugboats used 4 6-71’s for power and would really roar turning large ships around in the harbor.
One of the first trucks I ever drove was a 8V-92, the later version of the two stroke Detroit Diesel. It had twin turbos feeding the Roots blower, and still had that famous Detroit sound. Howard is right, a multi geared transmission was a must with the two stroke, you had to keep the RPM’s high to have any power. A lot had 13 and 15 speed transmissions. You physically had to drive them, no cruise control on those engines. The later 60 series are more forgiving engines, I’ve owned a couple of them, my last one got 1.1 million on it before it needed an overhaul.
Hi BA, oh we had cruise control. It was called a brick from home to put on the throttle.
Yeah, I figure some of them had a throttle cable, too. Used to pull the throttle cable on the old R model Macks when we were on the interstate, poor mans cruise control. Worked pretty good with the Macks, they had enough torque you didn’t have to change gears much after you got them rolling anyway.
Actually, these trucks ( Cannonball) usually had the 4-53 series engine ( good heavens) The 6-71, I believe, wasn’t popular until late 50’s or early 60’s. Believe it or not, many trucks still were gas jobs around that time, and many were just more familiar with gas engines. Cummins, Cat, and Mack were just more civilized, and could run circles around most Detroits. Not to say there weren’t some runnin’ Detroit’s. I knew a guy that had a V-12 in a Freightliner cabover ( he called it “The Buzzin’ Dozen”), not sure of the hp. probably in the 450-475 range,( that was a lot for the 70’s, when everybody else, including me, were driving trucks with 250 or 300 hp)) and that truck pulled away from everybody, but it never lasted too long, as he was constantly fixing it. Clearly, the 2 cycle Detroit hit a nerve with me. I was a trucker for 35 years ( now semi-retired)( pun intended), but there was a time when Detroits were king of the road.
Wonderful — the noise, and the comments as well.
God awfull noisy things. How did the drivers not go insane? Many did go deaf!
Drove a V6 GMC ONCE for about 10 miles in a semi tipper [originally used carrying fuel at an airport]. Went ok but yes you had to rev it to make it go. Especially carrying about 34 tonne gross. Torquless 2 stroke! Made our slow but torquey 354 Perkins feel easy to drive.
An operator had one in a 8 tonne [load] D series Ford cab over. Very quick, would go past me 2-3 gears up on hills but you could hear the thing 5k away!
A racer I know had one in an old Bedford prime mover towing a smallish pantech. Again performance was ok , probably quicker than their more modern Volvo but as he said 60k was plenty. He drove it wearing earmuffs!
A hotrodder restored an old Ansair bus as a camper. But heaved the 2 stroke in favor of a 454 on LPG. Though the exhaust still sounded a bit like the 2 stroke. Why?
Very well done! It’s got to be a 4-valve engine which would be a lot newer than the 2-valve version that would’ve been the primary power source for this one. The 2-valve motor, depending on the injectors, would put out anything between 160 and 200 hp while the 4-valve was anywhere between 195 and 238 hp. I might add that I don’t think you could get a Jake on a 2-valve.
Damn my mechanical profession anyways; it’s an occupational hazard. He’s got the Jakes set too tight; maybe needs to go through a complete top end adjustment; there’s a bit of a hitch in the idle.
Howard is so right! Drive one of these for an entire day and you’re ready to fight a grizzly bear. I occasionally drove a ’75 GMC 9500 with a 318 V8 (mostly under the floor). I remember a trip to transfer a couple of new (John Deere) tractors from another dealership. It was 508 miles one way. Up at 4:00, on the road at 4:20 and all day in that noise-maker. Came home toting 71,000 lbs. about 3:30 the next morning. My ears rang for three days afterwards. You need to wear earmuffs.
Hi GS, I know you’ve heard this one before, but for the others, I drove an early ’80’s Louisville Ford with a 238, and had a regular run from Madison, Wis. to Bloomington. ILL. ( about 4 hours, one way) came back, and parked it in the garage. ( absolutely no hint of trouble) came in the next day, my truck was gone. I said, “Bill, where’s my truck”? He said, after I got in, they changed the oil, and when they started it up, it threw a con rod through the side of the block. I was surprised, but happy to hear that, as a new motor meant maybe more power. When I got it back, it wasn’t any different than the old motor.
Hi Howard. A thrown rod is a very unusual failure for a ‘souped-up Yamaha.’ I’ve seen lots of them drop valves. The most frequent was to break rings (too much ether). We had a bulk fuel agent with a Chevy Bruin that had a 6V-53T (fancy sounding name for something that on its best day won’t pull a limp (noodle) from a pail of lard. Severe starting troubles–take half a can of ether to get it going. Once running it took 15 minutes for the smoke to clear. We pulled the air box covers off, looked inside and laughed. The rings were completely gone from (3) pistons, two pistons had just one left and, only (1) piston was intact. To make a long story short, the tuneup that ‘Slippery’ (the fuel agent) thought was getting done turned out to be a major inframe. And in a Bruin/Brigadeer? You have to raise a corner of the cab to get the liners out.
In the “Seabees” we had tons of equipment powered by DEE- troits. Generators, pumps, saws, rollers, rock dumps, etc.
the cool thing about them is the interchangeability, so keeping them going, rods, pistons. liners was a great thing. And what young kid out of High school doesn’t like to shift gears!?
I still help a farmer buddy pull crops from the fields just so I can drive his 6-71 twin stick grain truck each fall!
A 318 cab over, over the road truck would probably suck though….
Hi Al. The venerable ‘Green Leaker’ was very adaptable and could take no end of abuse yet still keep going. I would have to say that the military demonstrated that more than anyone. All branches of the armed forces used Detroits for something. It’s rather sad to see its dynasty fading away. And yes, driving a 318 sucks. Driving a 255 would be worse.
And when they run backwards, you’ve got 13 speeds in reverse and 3 forward. 🙂
I worked at a place where they had a Detroit engine that was used to power the fire system pump during power outages. Because it was in the basement of the building the air intake and exhaust were run up through the roof. The 500 (?) gallon fuel tank was at ground level.
We had a flood at the plant. About 2′ of water. Of course the basement were the Detroit was flooded. The Detroit had started before the flood and continued to run for a couple of hours completely under water. It was the strangest thing. Look across 2′ of water at the pump house that had water half way up the windows, and hearing the diesel running.
One disappointment in the video. He never opened the hood.
Had these as generators on Coast Guard Bouy Tenders loud! Took one apart once
because it was knocking. Undid the con rod bolts and it ran on 5 cylinders. con rod was
bent at about a 40 degree angle but it ran before we took it apart!
Here is an updated shifting video of the cannonball
Thank you for sharing.