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Old 09-24-2018, 09:48 PM   #1
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Detroit Diesel 71 series engines

Hello fellow TFers!
While reading another recent thread about engines I started to search info about Detroit Diesel 71 series engines. I am not owning any but reading history and information I was very interested about it (for my own curiosity/education).
I love old engines and I found really interesting the long history of the series and its architecture etc.
Would you have any story/info about these engines please chime in!

L
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Old 09-24-2018, 10:35 PM   #2
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I talked to some of the old-timers on shrimp boats back when I was a kid about the way things were long before my time. To them the "new" Detroit diesels were a luxury. The old diesels were single cylinder, direct drive, and you started them rotating backward when you wanted reverse.
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Old 09-24-2018, 10:43 PM   #3
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The Detroit diesel was designed to be a light weight high performance diesel. While rather complex, it completely achieved its goal. Of course we are talking about a WWII engine.
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Old 09-24-2018, 10:44 PM   #4
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Lou, I had 8v71 Detroit's. The 71 series, and it's cousins the 53, 92, 149 (and maybe other displacements) were designed in the 1930's. One elegant design element of these 2-cycle engines was commonality of parts. Many parts in a given series are the same regardless of the number of cylinders. Often criticized for leaking lube oil and being noisy, they are rugged and long-lived especially in lower output, naturally aspirated versions. There are thousands of these engines in workboats around the world. Parts are available and they are rebuildable. They just keep chugging.
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Old 09-25-2018, 06:40 AM   #5
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Lou, I had 8v71 Detroit's. The 71 series, and it's cousins the 53, 92, 149 (and maybe other displacements) were designed in the 1930's. One elegant design element of these 2-cycle engines was commonality of parts. Many parts in a given series are the same regardless of the number of cylinders. Often criticized for leaking lube oil and being noisy, they are rugged and long-lived especially in lower output, naturally aspirated versions. There are thousands of these engines in workboats around the world. Parts are available and they are rebuildable. They just keep chugging.
I read that the last 71 series engine was delivered in the 90s, this is a heck of a longevity for an engine that started to be built in the 30s!

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Old 09-25-2018, 07:16 AM   #6
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The 6-71 is unique that it can be assembled to have either rotation ,

this can easily be changed later, and service items on either side, your choice.

Power can be adjusted with different sized injectors, and different timing , adjustable.

Power is 20-30 HP per cylinder for long life ,,75 HP for 1,000 hours sport fish.

Nice for boat builders. Not light (unless aluminum blocks for minesweepers) .

Great engineering for 1936 , killed by air police .World wide parts sources , will probably go another 50 years.
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Old 09-25-2018, 07:33 AM   #7
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I saw that the first inline serie was available in 1 to 8 cylinders, the 3-71 output was around 130hp, quite good for a 3 cylinder engine!
Was there any drawback about these 2 cycle beside the oil leak and noise mentioned above?
Also what was the cause for these known leaks?

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Old 09-25-2018, 07:57 AM   #8
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Greetings,
Mr.L_t. I don't really know all that much about 71's other than my BIL had a pair of 425 HP's in his sport fish BUT his 6-71's were honkin' big engines. So I expect weight would be a drawback in certain vessels.
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Old 09-25-2018, 08:17 AM   #9
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Nothing sounds better then a DD starting up in the morning....
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Old 09-25-2018, 09:34 AM   #10
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Nice for boat builders. Not light (unless aluminum blocks for minesweepers)
I had a pair of aluminums in my previous boat. Engines were 50 years old and I had just rebuilt them. The PO had cruised that boat from the Great Lakes to Aussieland and back - during the same time that Jacques Cousteau was amazing us with his exploits. Reading the 3 inch thick ship's log was like reading a novel by Jules Vern.

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Nothing sounds better then a DD starting up in the morning....
Not sure I agree with that. I suffered some serious noise fatigue when out at sea for a week or more at a time. Perhaps a few thousand bucks worth of high tech sound insulation would have helped. Even performing engine room checks when underway did require putting on ear protection.
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Old 09-25-2018, 10:13 AM   #11
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I did preference it to "starting in the morning"... I know a good number of people who go through that fatigue in down east boat with the big diesel in the wheel house and stack right near them and it didn't matter what brand of diesel, but I get your point for sure!

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Not sure I agree with that. I suffered some serious noise fatigue when out at sea for a week or more at a time. Perhaps a few thousand bucks worth of high tech sound insulation would have helped. Even performing engine room checks when underway did require putting on ear protection.
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Old 09-25-2018, 10:21 AM   #12
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They leak oil out the access covers and plates that make them so inspectable and rebuildable. If you keep on top of things using modern sealants they can go a fairly long time between drips.......
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Old 09-25-2018, 11:05 AM   #13
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I worked on steel hull fishing boats as a kid starting at age 12 (Pinhead, cleaned the decks in order to fish for free), and then eventually a deckhand through High School. Most of the boats had DD's. Thousands of hours on the water back then and never witnessed a major mechanical at sea.
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Old 09-25-2018, 11:51 AM   #14
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I think I'm like most of the guys here who have previously owned Jimmies, with true sentimental feelings about these amazing pieces of machinery. Buying an existing boat with them would be fine and certainly in no way a negative. However I have seriously considered, and have decided, that I would not install them in a new build.
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Old 09-25-2018, 02:03 PM   #15
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They still make the 471, probably for outside the US. I don't know of a more reliable engine, even in very old age. 671 blocks were made in cast iron, aluminum and stainless steel (minesweepers). When I was a fisherman, late 70s, the inline 671 was still the most common engine. 8v and 12v were in bigger boats. 371, 471 and 53s in smaller boats. The inline 71s were made in a 1 cylinder version. Usually DC generators. The 1-71 will run about a 10kw AC generator. Ships usually had a 71 emergency generator. Lots of boats had WWII surplus engines, some never overhauled.
In the navy during Vietnam, all the patrol boats had DDs. There must have been thousands in the USN.
Thanks for this post. I love talking about these engines.
My first boat in 1961 had twin 671s and my current boat has nearly identical engines. The oil leak problem isn't nearly as bad as most people think. Most of the leaks come from the rear main seal. Older engines have an old style rope seal.
You can run the natural 671s 20,000 hours at their maximum rated rpm. I've done it.
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Old 09-25-2018, 02:49 PM   #16
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During WWII, if you needed more hp, they would bolt on more 200 hp 6-71's connected at the crankshaft IN TANDEM


Example 151' LCI(G) specs that my dad served on:


Propulsion two sets of 4 GM diesels, 4 per shaft, BHP 1,600, twin variable pitch propellers
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Old 09-25-2018, 03:10 PM   #17
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During WWII, if you needed more hp, they would bolt on more 200 hp 6-71's connected at the crankshaft IN TANDEM


Example 151' LCI(G) specs that my dad served on:


Propulsion two sets of 4 GM diesels, 4 per shaft, BHP 1,600, twin variable pitch propellers
Or a quad installation, and on a single screw. USS Cape, MSI2.

“Keeping the Salish Sea Mine Free since ‘93.”

For sale here:
https://www.yachtworld.com/boats/195.../#.W6qGsIFlChA

Given enough money, what an awesome project that would be.
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Old 09-25-2018, 03:24 PM   #18
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Quote:
Originally Posted by High Wire View Post
During WWII, if you needed more hp, they would bolt on more 200 hp 6-71's connected at the crankshaft IN TANDEM


Example 151' LCI(G) specs that my dad served on:


Propulsion two sets of 4 GM diesels, 4 per shaft, BHP 1,600, twin variable pitch propellers
Indeed, I just read the owner manual for the 3/4/6-71 and they were describing the connected twins or quad engines, really amazing!

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Old 09-25-2018, 10:09 PM   #19
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The DD series has the advantage of tremendous torque because of its 2 cycle design. I’ve run them for 50 years on our family’s oyster luggers in 3,4,6, & 8 cylinder 71 series configurations. IMHO no modern 4 cycle Diesel engine can compare to the throttle response, the acceleration (torque rise) of the DD. The last lugger we built with a Detroit had an 8-71 NA in 1986. That engine is now 32 years old with over 30,000 hours without major overhaul nor major breakdown. During oyster harvesting which accounts for about 80% of the engine hours the engine runs at around 800 rpm. Although I’ve heard so much about how bad low speed operation is on diesels, we never experienced that on the workboats around here with the Detroits.
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Old 09-25-2018, 10:28 PM   #20
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Detroit Diesel 71 series engines

Ive got twin 6-71’s, one has about 100 hours since a frame in rebuild and the other has about 150 hours, great efficient engines, I run them about 1400 and get 1.6 mile per gallon between the two, pushing my 65’ Boat about 9mph
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