DD two stroke engines

[Hank]

I'm curious why the 2 stroke engines gained such popularity in the transit sector. Was it because GM was a major producer of buses for so long and all other manufactures (MCI, Eagle, Prevost) just figured they should use them too? Was it a size consideration (shorter block)? How did Detroit Diesel get such a foothold in the marine sector? Another thing that doesn't make sense to me is that 2 stroke engines typically get around 300,000 miles before needing some level of overhaul whereas some 4 stroke diesels can get twice that if not more before an overhaul-so why would an OEM spec their equipment with an engine that has a known lifespan of at least half of other similarly powered diesels? It doesn't appear that it's any cheaper to overhaul a 2 stroke! Were they just that much more reliable? Also, 2 strokes use a lot of oil compared to a 4 stroke which make it more expensive to run and requires more PM. Wouldn't that deter OEM's too? Questions, questions, questions! I'm interested in a little history lesson on Detroit Diesel's 2 stokers or a link to any relevant websites if anyone knows.
Thanks,
Hank

[tekebird]

Hank,

back in the 50's when this all started....maybe even late 40's the DD was one of the most reliable powerplants out there.  and as a two stroke they are stone age simple unliuke a  four stroke.

I am sure others on the board have alot more in depth history combined with tech data.

I suspect that early 4 strokes didn;t get any better mileage (TBO) than a 2 stroke, and I suspect used similar ammounts of oil.......now with that said, a properlymaintained Detroit does not have to use any significant ammount of oil...perhaps a few Qts ever few thousand miles.

just as with people saying the 6-71 or other two stroke is low on power....I think most would find that they are just running tired engines.......there are few out there that have low mileage or new DD crate engines to compare to, and by the nature of the beast your average conversion owner does not know diddly about the history and prior maint of his particular powerplant...other than what the prior owner told them.

I would hazzard a guess that the 71 series engine is the ost produced and has the highest logevity as a group whole of any other powerplant produced for  commercial service.

someone a while back posted a number of 71's that are still plying the roaqds and waterways as well as running pumps, mills generators etc.

It was quite impressive and likely an underestimate.

[TomC]

Detroit Diesel, originally GM Diesel, brought out their first engine in 1938-just in time for Gray Marine to introduce them into the landing craft during WWII.  When introduced, they were considerable smaller than any 4 stroke engine since turbocharging was just in its' infancy, being used primarily in expensive aircraft engines and primarily by the military.  The 6-71 was so versitile, on a larger landing craft that needed twin 600hp engines, rather than creating a huge engine room for two giant in line 8 cylinder train engines, they just hooked four 6-71's together in a bull gear, so that 8 relatively cheap engines achieved the same result as the very expensive and heavy train engine.  Then too the engines one at a time could be serviced while under way.  The 6-71 also has seen service laid down under the bus floor on both Crown and Gillig school buses, and stood vertically for space saving generators on oil rigs.
Even in the 80's when the 92 series were being used, they were still around 400lb lighter than the closest Caterpillar or Cummins engines, and got very close to the same mileage.  Oil consumption was accepted (I had one and got 2200miles per gallon of oil).  On my 8V-92TA, there was a definite schedule of maintenance you needed to do.  Every 100,000 miles run the injection rack; at 200,000 miles, roll in new bearings; at 300,000 miles overhaul the blower, turbo and injectors; at 400,000 miles roll in new bearings; at 500,000 miles usually a complete overhaul.  At this time, both Cummins and Caterpillar were getting about 250,000 to 400,000 miles before overhaul.  Only recently with the advent of electronic fuel injection with air to air intercooling have the engines been able to go towards one million miles before overhaul.
Because of the small size of the 2 stroke, most buses were using them.  Since Detroit stopped making the 2 strokes in 1998, the bus companies had no choice but to go to the 4 stroker.  The engines that are very close to the 2 strokes in size, weight and power are the Detroit Series 50; Cummins ISL, ISM; Caterpillar C9, C12, C13; and Volvo 13 liter.  Buses have to be modified for the Cummins ISX, Caterpillar C15, C16; Detroit Series 60, DD15.  
Personally, if you're thinking of changing out your engine, I would not consider the 2 strokes anymore-they are getting harder to find mechanics that know how to work on them (and they do have their own quirks).  I think the either the Detroit Series 50, Cummins ISL at 400hp, or the Cummins ISM are good engines to switch with.  Good Luck, TomC

[Dallas]

Hank,

Gotta agree with Doug on this..

The 71 series Detroit Diesel was released for public use in 1938. It had been in development from somewhere around 1930, and had been in Military testing for most of those years.
My ex-father in law was a tank commander during WWII and had been in the testing program at Ft. Knox from the early to mid 30's.
He told me about running the MkII and III tanks at 27MPH with the gas engines as delivered from the factory, (GMC and Continental mostly). He told me they loved to put the 4 and 6 71's through their paces compared to the gas engines because they would continue to to run as long as there was no blockage in the air intake or the fuel system.

I've been a diesel mechanic for as many years as I've been able to read and worked with them since before that, (our trucks and logging equipment ran mostly Detroits and Cummins'). The Detroit doesn't leak or burn oil as a habit, it burns and leaks oil because someone didn't build it correctly or take care of it after it was built.
My 6-71 (2-valve) topped Jellico Mtn. at the Tn-Ky border at a speed of 45 mph, better than many of the MCI 102DL's and E models here at the bus company I am parked at. Most of those with the Cat and Cummins and Detroit 60 series engines can only get up that hill at 38-41 mph.
Since we left South Carolina in July 2007, we've put well over 3,000 miles on our bus. It has an old, tired, engine with one injector that doesn't belong. We average 9.8 to 13.67 mpg for fuel and have only added 1 gallon of oil in that time. The oil was the result of a leak in the air compressor.
300,000 miles? I ran a 1974 KW K-100E with a RTOO9610/Detroit 318 turned up to 360HP/2450RPM for well over 500,000 miles before I had to rebuild... it dropped a valve. My average load was 88,0000 lbs with many exceeding 200,000 pounds.
I never had a starting problem even at -40°(using preheaters and ether, of course), A lot of the loads I hauled were on the dirtiest roads in North America.. the haul road to the Alaska Pipeline and one you have heard of recently... the Ice Road in Canada.
Comparatively, I've had a few newer trucks with Cummins NTC BCIV 400HP, 470HP and one at 625HP that would eat oil from the day I bought them and go through massive amounts of fuel.
I also had a few Cat 3406's that were heavy and sucked when it came to fuel, but would pass up anything else I had on the road. these weren't high HP engines, just standard 325-470HP engines. they were good with oil usage though, a couple of them would never use even a cup of oil between oil changes.
Detroit 2Strokes are great for certain usages especially in bus service... One reason is that the 2 stroke can be run either clockwise or counterclockwise. This means that the engine can be turned sideways, run backwards and deliver all the power needed to move a load of passengers and freight, without the need of a reverser gear on the transmission.
In marine service the DD2stroke is many times put in tandem .. one being Clockwise and one being counterclockwise. This keeps the torque from tearing the hull apart. Even the large Pusher boats and Navy YTB's used the Detroit for motive power.. A few Destroyer Escorts were even outfitted with a series of Detroit 6-278's. 30 knots ain't nothing to sneeze at.

One other reason the Detroit was so popular is that the other engine makers, ie Cummins, Perkins, Mack and some that don't even exist anymore couldn't even come close to the power and reliability and longevity of the DD. Many of the 1950's diesel engines from Cummins were only rated at 150-170HP. It wasn't until the mid to late 50's that Cummins even got past the 200HP mark.

You also need to understand that the DD is (or was) the world leader in innovation. Some of the marine versions of the 71 series 6 cylinders were putting out well over 500HP with a life expectancy of many years.
Cummins tried to compete with it's 903V and 903VT but couldn't match the life span. Truth be told though... in a combat situation, those 903's would work circles around a 8V71, considering that some of them had a battle setting at 1100HP, too bad the Cummins engine would die after a week of that kind of power.

Another thought to put to you is that the largest and most fuel efficient engine in the world is a 2 stroke, derived directly from the DD 1930's design. Here's a shot of it:

http://people.bath.ac.uk/ccsshb/12cyl/

http://k4viz.com/12-Cylinder.html

For fun:
http://gcaptain.com/maritime/blog/the-wartsila-sulzer-super-engine/

[DrivingMissLazy]

Back in the heyday of the engine I do not believe that the cost of the oil used was even a consideration to most users. Probably less than 1$ per gallon. Hardly can buy a cup of coffee for that nowadays.

Back then I would check my automobile oil level at each fuel stop. Now it is not even checked except when time to change it.

Richard

[Stan]

Just a couple of things that I am familiar with. The DD had unit injectors so the engine would always get the bus home, even with one or two bad injectors. All the four strokes with injector pumps were dead on the side of the road with any pump trouble.

However, the biggest reason for their popularity was repair cost. Because of the standardization of parts for the whole 71 series they mass produced parts and sold them cheaply. They had a deal with MCI (prior to Penske) that let me buy DD engine parts below the local DD dealer's cost.

[blue_goose]

In the past I have read that the Detroit Diesel was used because it was the only engine that would put out enough heat to heat the bus in the cold weather.  The cost of fuel wasn't a problem, because it was cheap.  I read this in a artical in the bus trader.  I was the history of busses, can't find it now but maybe someone else can add some more to it.
Now all buses have to have heat othere than the engine to keep the people warm.
Jack

[HB of CJ]

No, no and NO!  While the above answers/reasons are very good and complete, we all know the REAL REASON why the 2-stroke Detroits were soosss successful.  It's because they sounded soossss... BITCHIN'! 

[oldmansax]

Along with all of the reasons already mentioned, a DD will START! We had a '54 Autocar with a 170 Cummins. That was the precursor to the 220, which was the precursor to the 250, 335, 400 etc.

I remember building a fire under that miserable Cummins  & using 2 battery chargers & 2 guys to get it started. .... One to pull the compression release and one to try to start the truck.  And the 2 chargers? One for each 6 volt battery bank. Remember, those old engines started on 12V and ran on 6. Can you say "Parallel Switch" ? Another miserable piece of equipment!

My first 671  earned me a lot of ridicule until Dad and I both got ready to leave out one frosty 15 degree morning. I shoved a little ether football in the starter cup, & fired up that old 671 while Dad was building his first fire.

When he caught up to me at Le Hi TruckStop, I had already eaten and had 2 hours sleep. He never ran down my DD again.

I also replaced one hole in a 8V71 in the rest area between Gainesville and Atlanta GA. Try that with a Cummins.

Sorry, I tend to ramble..........

TOM

[Barn Owl]

One more reason: Incredibly smoooooth! Lots and lots of firing pulses meant from idle, to full governed speed, a comfortable ride for the passengers.

[Fredward]

I don't know guys......Six miles from here is a 35 year old self employed truck/diesel mechanic with more work than he and one other guy can handle. He loves Detroits. He has repowered some wheel loaders with rebuilt detroits. They had Cat 3208 or who knows what in them. He has an Oliver farm tractor that he put a 6V92 in thats got huge injectors and is putting out about 700 horse. He competes with it locally in tractor pulls. He runs the rack on that engine each time he pulls with it.

He used to work for a contractor that had lots of old Detroit powered equipment and learned from the "old" mechanics how to fix Detroits.

So there are still some guys out there; maybe those of us in central Minnesota are just lucky?
Fred

[gus]

It has been very interesting reading these posts, a lot of really good information that I will archive.

I love my 671, I love the smoothness and sound of it but I wish it had more lugging power.

For a big truck I prefer the Cummins because of its lugging power and ability to idle for a week with no problem.

Otherwise I prefer my 671.

[TomC]

Gus and all others that are running non turbocharged 2 stroke engines.  I can say without a shadow of a doubt that turbocharging and air to air intercooling a 2 stroke really wakes up the engine.  My 8V-71 went from 300hp and 800lb/ft torque to 375hp and 1125lb/ft torque and without smoke at full throttle-big difference in performance-about the same fuel mileage.  Good Luck, TomC

[jackhartjr]

Dallas...an exception to what you wrote on the VT903, (VT 90-Nothing LOL) was that a trucking company I worked for in the 80's and 90's (For 15 years) Thomas Produce, later Thomas Transport, Greensboro, NC bought a bunch in the lates 70's early 80's.  Cummins told them for every one they brought in without an overhaul in 1,000,000 miles...they would give them a new one!  After what I think was 7 new ones, Cummins said, "Look, we have to stop this!"  (We ran west coast, team, we could put a million on in just over 4 years!)
If that engine did not ever run hot, and if the oil was changed regularly...you coundn't stop them!
(Of course when it saw a hill...it jumped into high range reverse!

Most folks I have talked to that had them in their boats love 'em!

Jack

[lostagain]

I'm with Tom on turbo charging.
I turboed my 4-71 and it makes a very noticeable improvement. I now go up the hills one gear higher, (5 speed Spicer). No more smoke either.
The 71 series DD is by far and by all measures the best diesel engine ever produced, just like the Courier 96 is the best looking bus ever built... Ha, ha!