Diesel Two Stroke

Nowadays if you want a DD, I'd suggest a Cummins, remove the muffler, and pour a gallon of oil over the engine. It will be just like the old days.

DD need not leak at all.

Our 6-71 was a 1954 or so Grey Marine unit that was placed in a sealed can as war reserve and stored somewhere till the 1990's.

As it was never worked on by boatyard wrenches , it never leaked at all..

I am surprised that new DD are not fitted with exhaust cats and DEF , so the air police would not ban them.

FF said:

DD need not leak at all.

Our 6-71 was a 1954 or so Grey Marine unit that was placed in a sealed can as war reserve and stored somewhere till the 1990's.

As it was never worked on by boatyard wrenches , it never leaked at all..

I am surprised that new DD are not fitted with exhaust cats and DEF , so the air police would not ban them.

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Pretty cool. So Gray Marine is what become Lugger/Alaska Diesel. They have an old Gray Marine engine in their lobby.


When you refer to the "new DD" are you referring to the current 4 cycle models, or are you suggesting revival of the 2 cycle with added emission devices? The 2 cycles (other than very large engines) went out of production a long time ago, no?

I believe the 71 series 2 cycle stopped production in 1994. The 4-71 was still built for some applications after that.

Because the injectors are mechanical it would be difficult to change emissions without going to a computer operated injector and then reliability goes out the window. 71 series, 2 cycles will run reliably when the rings and sleeves are badly worn out and the oil pressure is down to 15psi. Without a computer, the engine doesn't know or care.

"Because the injectors are mechanical it would be difficult to change emissions without going to a computer operated injector and then reliability goes out the window."

My hope would be there might be some improvement in mechanical injectors since 1936 .

Otherwise the exhaust components could be sized to lower the exhaust "bad" output with a new bigger cat +more DEF ..

Of course the politicos keep raising the bar (no cost to them to claim to be a clean freak) so no iteration of clean will do.

Remember the exhaust from a big truck may be cleaner than what goes thru the intake on the NJ Turnpike and other areas.

Well,here's my .02cents worth.
As a "retired"(haa haa)road musician, I've only owned busses with DDs in them. 2 6/71s and one 8v53 in a 4501 Super Scenic Cruiser(#194).
They may be noisy,but those are absolutely the toughest engines I've ever seen. If you let them idle tho,they will dump all the oil out(thus, the "fast idle"knob on a bus).
As for marine engines,I've had a Pacemaker Sport Fisherman with twin 6v53s,a 1969 45ft Matthews TCFD with twin 8v53s,and ,my current boat,a 1969,42ft Grand Banks, with twin 4/53s. Strangely, this boat came with twin Daytona Diesels,which,from my understanding, were a pile of junk. The 4/53s were installed in 1984,and now have approximately 3500 hrs each on them.
Yes,they're loud
Yes,they slobber oil
Yes,they take up a lot of room
BUT,
YES,they start
Yes,they ARE fuel efficient
Yes,you can get 12,000-15,000 hours out of them,if you keep them serviced,which,by the way,is easy.
For every 15 units of fuel sent to them,they use one. Meaning that the fuel gets polished over,and over,and over.
I can run used cooking oil, used motor oil,used hydraulic fluid, ect.
And my I say.....
Any marina that "was glad that my loud DD left,"is a marina that I would not want to be in. Sounds a little "high-falooting"(sp?)to me. Any one who would look down their noses at someone simply because they don't like the sound of their motors,is,in my humble opinion, a snob.

Best exhaust note marine engine ever built...just music to my ears!
You just cannot beat their simplicity and reliability, she will get you home everytime.
No glow plug/pre heater needed, no injection pump to deal with, built in fuel polishing...
Both my 671s clocking close to 10,000 HRS & still purring.

NUTIN FANCY TOO said:

Any marina that "was glad that my loud DD left,"is a marina that I would not want to be in. Sounds a little "high-falooting"(sp?)to me. Any one who would look down their noses at someone simply because they don't like the sound of their motors,is,in my humble opinion, a snob.

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There's a big difference between a noisy boat and one that's just downright obnoxious. When you can sit in the salon (with the doors/windows closed and music on) and a boat starting up in its slip 300 feet away with the exhausts pointed away from you, it counts as obnoxious.

Fortunately, the one Detroit powered boat in my marina is fairly well muffled, so it's only "kinda loud", not obnoxious. My dock neighbor's Formula with minimally muffled 502s in it, well, that's obnoxious. It's not straight dumps of the headers speedboat loud, but still quite loud. We were both heading out at the same time one day and without looking at the tachs, I couldn't even tell my engines were running (at high idle) over the sound of his. Even standing in the salon directly above my engines, his were far louder than mine.

Screaming Green Leakers.....That's Funny!

Yes, my Turbo 6-71's are a bit noisy. Hardly leak. And I have actually been complimented on the exhaust note.
But mine are painted White. I must be a snob....

dwiggl said:

Screaming Green Leakers.....That's Funny!

Yes, my Turbo 6-71's are a bit noisy. Hardly leak. And I have actually been complimented on the exhaust note.
But mine are painted White. I must be a snob....

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Mine are "dirty white". I must be a redneck snob.!!! Lol

In Vietnam I ran PBRs with twin 6v53s in a special ops configuration. The engineroom was well insulated, about 1 foot of foam, and the exhaust, after being muffled, was released underwater. At idle, you could only hear the splash noise of the water jets. And at full throttle you could only hear them 25' into the jungle. We normally cruised just short of flat out. DDs don't have to be noisy.

NUTIN FANCY TOO said:

Mine are "dirty white". I must be a redneck snob.!!! Lol

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Ours are yellow... not sure why, but when they were overhauled the owner had them paint everything cat yellow.

No glow plug/pre heater needed, no injection pump to deal with.Injectors are DD injection pump.

Glow plugs are required on engines that use a pre combustion chamber.

The DD have to use a shot of ether in below freezing , or a special cranking technique , tho best is a coolant heater in the block.

"the "fast idle"knob on a bus"

."Exists to spin the gear driven air cond compressor fast enough to heat or cool the bus.

Most require 60 hp and help the warmup.

DD

IronZebra said:

I have been doing a bit of reading on Detroit Diesel and the 2 stroke design. They are very interesting. I found this YouTube video very informative on they way they work. Because I had such a hard time finding a good explanation I thought I would share should some one be looking in the future.

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The old truck drivers used to say if the truck has a Detroit in it " slam your hand in the door and drive it like you hate it"!
With all the new sealants and gasket materials available the old slobbering problem has been eliminated. There still seems to be a strong demand for those motors in all kinds of applications.

471 is pulled out again,
Take a look at those bearings, they are bigger & thicker much more stout than DD's V series.
One more reason 71 inline series runs forever.
Anyone knows why this freshly rebuilt DD's engine oil is so dark?

https://youtu.be/adThi_8r4Lk

Dangar Marine is rebuilding his 471 again after someone totally botched his first one. This time he has found someone who REALLY knows his Detroits and explains the faults and general operation principles very well in plain language.

https://youtu.be/adThi_8r4Lk

***Sorry, I didn't realise the post above referred to the same link. I'll leave mine up as +1 to the informative video.***

It's a shame that the first builder he used didn't know what they were doing.

I guess they didn't even have the book, it's crystal clear that you have to install the wrist pin caps with a dished tool and then vacuum test them to make sure they seal. Instead they decided to smack the pistons with a center punch! Hopefully he will do another bench test start there at the workshop. That's always fun. I really enjoyed doing mine, but I was pretty nervous having never started a Detroit that wasn't bolted down in a machine. With no exhaust is is very loud.

Here's my first start after rebuild. Camera is shaky and kind of all over the place, but it's all about the sound anyways.

One reason for smooth long life is 7 main bearings on 6-71 .


Most will idle at 350 - 400rpm and still not shake.

Along with DD's Series 60 another nail in the 6-71 coffin was the Cat 3406. The 3406 diesel is that good, much sought after and still in production after 30+ years.

By the mid 80s the handwriting was on the wall for the DD 2 stroke. Reliable, powerful for engine weight and emissions compliant 4 stroke diesels transformed the industrial buyers.

Fortunately for us low hour usage 2 stroke aficionados fuel is plentiful and parts will be around for awhile.

FF said:

One reason for smooth long life is 7 main bearings on 6-71 .


Most will idle at 350 - 400rpm and still not shake.

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Moreover it is the fact that you get all cylinders firing in one revolution - less torsional vibration with multiple lower pressure firing cycles in a shorter period of time.

We can idle the EMD engines at 250RPM in gear, 8GPH and respond to clutch commands without stalling...same principal but more mass being spun.

If I set the idle on my 12-71’s too low they will chirp the low oil pressure alarm and occasionally stall if shifting into gear against the boats movement. 36x36 inch props have a lot of resistance, especially when pushing against the boats momentum.

And nothing sounds as good as an idling Detroit V-12! I will admit to being ignorant of the sound of a V-16 though.

Lepke said:

In Vietnam I ran PBRs with twin 6v53s in a special ops configuration. The engineroom was well insulated, about 1 foot of foam, and the exhaust, after being muffled, was released underwater. At idle, you could only hear the splash noise of the water jets. And at full throttle you could only hear them 25' into the jungle. We normally cruised just short of flat out. DDs don't have to be noisy.

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Thank you very much Lepke.
I’ve always thought so.
Noise is noise and a “foot of foam” sounds like they took the job seriously. That’s the problem w yachts. They just don’t take the job seriously. They are big shots and who will tell them it’s too noisy?

FF said:

One reason for smooth long life is 7 main bearings on 6-71 .


Most will idle at 350 - 400rpm and still not shake.

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Exactly!
Here's a good video By BGM...much more robust, more than twice bearing surface than their cousin V configuration series.
My 671s are set @500 & do not use the buffer screw to adjust idle RPM


https://youtu.be/hWfgUOK2xwQ

Nomad Willy said:

Thank you very much Lepke.
I’ve always thought so.
Noise is noise and a “foot of foam” sounds like they took the job seriously. That’s the problem w yachts. They just don’t take the job seriously. They are big shots and who will tell them it’s too noisy?

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That is a bulletproof Uniflite 31 hull MK1 or MK2 with twin DD with Jacuzzi jet.

Charlie still don't surf....

dwiggl said:

Charlie still don't surf....

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Maybe not then, but he does now! He also owns the bungalow resort and bar/restaurant on the shore too. A lot has changed since Charlie won the war......

Ruffryder said:

That is a bulletproof Uniflite 31 hull MK1 or MK2 with twin DD with Jacuzzi jet.

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I was working at Uniflyte in the early 70’s when these guys were being made. Don’t remember the bullet prof feature but it was probably there ... I just don’t remember it.

When I worked at Washington Iron Works in South Seattle I had the pleasure of frequently hearing DD engines start up. But when they reved them up do some work it was definitely noisy. WIW was a very large manufacturing facility not unlike a WWII train depot. Lots of train tracks inside but I don’t remember them being used. I don’t remember them using any other engine in the logging equipment they typically manufactured.

Nomad Willy said:

I was working at Uniflyte in the early 70’s when these guys were being made. Don’t remember the bullet prof feature but it was probably there ... I just don’t remember it.

When I worked at Washington Iron Works in South Seattle I had the pleasure of frequently hearing DD engines start up. But when they reved them up do some work it was definitely noisy. WIW was a very large manufacturing facility not unlike a WWII train depot. Lots of train tracks inside but I don’t remember them being used. I don’t remember them using any other engine in the logging equipment they typically manufactured.

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Very cool!
by the 1980s Uniflite had turned into the country’s biggest production boat builders.
Company like Grand Banks are now copying Uniflite's lines after 50 yrs later.

"If I set the idle on my 12-71’s too low they will chirp the low oil pressure alarm."

On GM coaches the air cond requires about 60-80hp

.GM coaches were monocoque , light weight aircraft style construction. The compressor has to be engaged at very low speed to keep it from ripping apart the mounts. A slow, slow idle was required.

GM used the low oil pressure light as part of the safety system to allow the system to engage the compressor.

With the low oil pressure light on a 9 inch chevy truck clutch was released to take the load.

Low oil pressure at idle is normal for many DD .

FF said:

"If I set the idle on my 12-71’s too low they will chirp the low oil pressure alarm."

On GM coaches the air cond requires about 60-80hp

.GM coaches were monocoque , light weight aircraft style construction. The compressor has to be engaged at very low speed to keep it from ripping apart the mounts. A slow, slow idle was required.

GM used the low oil pressure light as part of the safety system to allow the system to engage the compressor.

With the low oil pressure light on a 9 inch chevy truck clutch was released to take the load.

Low oil pressure at idle is normal for many DD .

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This is true. "Low oil pressure "is kind of an oxymoron in a DD. One of my old tour busses had ,maybe, on a very cold day,about 18 lbs of oil pressure at startup. Then,at operating temperature, 5-7 lbs. And we ran the tires off of it. But,as long as a DD has any oil pressure, it's good to go.
When I first went to look at my GB, I was told it would either have FLs,or Cats. I would have been happy with either. But,when I opened the floor up and saw those 2 DDs,I was halfway glad,and the other half disappointed. Glad it was DDs in there, because I've had nothing but good service from the 5 other DDs I've had but not so glad because of the volume in the salon being a little more than expected.
That being said, I am happy to take a little extra noise to have those bullet proof babies beneath my floors. Keep clean oil in those babies,and they will outlive me and my children. For me,the simplicity of them make it easy for anyone to be able to learn the basics of how to do their own service work. (Except for the "Armchair Admirals "). Anyone willing to get their hands dirty can take care of their own motors.
And,could y'all please talk a little louder? My hearing ain't as good as it used to be. Lol