DD 12V71TI question

[STraenkle]

Anyone have issues with these motor, other than oil sling dump truck? Just looking at some boats and they all have these engines, mid 1980's, but all say major overhaul. Which could mean they changed the oil, but just wondering about the model of the engines.

[Harry Babb]

Personally I like the engines. I have tuned and worked on several of them in Work Boats and in over the road trucks......and completely overhauled 3 V12-71's.

Other than the fact that they are "Old Technology" (and leak oil) the engines are work horses.

I do know that some of the external parts, pipe etc., for Heat Exchanger applications are getting very difficult to find......but the good thing is that the castings on the ends of the pipes are usually still good and only the copper tubing needs to be replaced.....very doable.

As far as internal engine parts, there are many aftermarket companies still making the replacement parts.

I would rather purchase a boat with worn out engines and have to rebuild them than have to do 1 minutes worth of work on fiberglass.

Major overhaul to me means out of the frame completely disassembled and brought back to new specs..........the counterpart to a "Major Overhaul" is refered to in our area as an "Up and Down".....which consist of cylinder kit replacement, main bearings, rod bearings, oil pump, reman heads and injectors.....plus a few incidentals such as hoses.

In work boat applications I think the guys generally count on 10,000 hours between overhauls.

hb

[STraenkle]

Thanks Harry for the reply, I thought they were ugly, but reliable engines. There are 2 types I am seeing, 800 Hp and 900 Hp versions. From Detroit Diesel page they call the Intermittent-maximum at 800Hp and Maximum at 900Hp, anyone know if the internals are the same and just larger injectors, etc. or very different, like a 2 bolt main chevy 350 and 4 bolt main? The 900 give a better cruise speed. all says about 500 to 1500 hours since Overhaul, so pretty light on the hours.

[MarkD]

Scott:

You going bigger and replacing the 31?

Mark

[STraenkle]

31 is not going anywhere. Just getting rid of the big house. All the kids are at college, don't need 6,000 sq ft. , but a movable vacation home would be nice.

[John F.]

I like the way you think

[Harry Babb]

Its been 25 years since I had my hands on a DD Diesel. So what I am telling you is OLD information.

Some of the Detroit's had a single piece piston.....may be the 53 Series but most of the ones I have rebuilt had a 2 piece piston and I think they refered to them as "Crosshead Piston's". I am pretty sure that all of the internals are the same, they just add more fuel, turbo's and RPM.

I am surprised to hear that the engines you are talking about are rated at 800 and 900 HP......I thought they were more around the 450 to 600 HP range.

Funny thing.....when I worked at the Mack dealership a customer came in with a Cabover powered with a V12-71 and a 13 speed Fuller transmission. The guy wanted "Advanced Cam Timing" and us to install C-80 injectors......she was a beast when we were finished......he claims to have been able to accelerate going up hill grossing 80,000#.

If the overhaul was done correctly the engines you are talking about have lots of good love left in them.

hb

[Navatech]

OK, 1st of all, you should look at the hours... Then you should look at their usage mode... An engine not doing anything for weeks on end and then doing a couple of hours out on the water is going to be "longer in the tooth" then an engine that was used far more often...

Little known fact, DD manual specifies that if these engines (71 & 92 series) have stood for a month or more you HAVE to use an external pump to prepressurize the oil system... The reason being that the oil has all dripped into the sump and if you don't pre pressurize the oil system you're basically starting up a "dry" engine...

2nd, somebody mentioned 10K hours between major overhauls... Yes, some 71/92 series DD's have done 7, 8, 9 and 10K hours before being overhauled but those were without exception so called NA (Naturally Aspirated) DD's... Of course, as everybody (should) know, there's no such thing as an NA DD 71/92 series... Even the so called NA has the supercharger blower... It's inherent to the engine's design... NA in this case really means non turbocharged... That means low load engines... Think a straight 6 or 8 cylinder installed in a trawler type of vessel...

DD was very conservative in their ratings and under "normal" use you're looking at roughly 1,800 - 2,200 hours between overhauls... I'm assuming normal maintenance... HOWEVER, if the engine was "marinized" by one of the other outfits (e.g. Johnson & Towers a.k.a. J&T a.k.a Junk & Trash) then you're most likely looking at a souped up version... These sometimes deliver less then 1,000 hours between overhauls...

As far as HP goes, my own DD 8V92TI's are rated at 575 HP and that's bog standard DD OEM... IOW, at ratings of 800 - 900 HP for a V12 you're looking at bog standard DD OEM ratings which is a good thing!...

Speaking for myself, if a manufacturer offers what's basically the same engine in, for example, 600, 675, 750 & 825 HP (different injectors, turbo's and so forth) I wouldn't recommend getting anything but the first two... In a pinch I'd go for the 3rd higher rating... I'd never go for the highest rating... That is if you're looking for reliability and longevity...

FWIW, there's a reason these engines in their various (3, 4, 6 and 8 cylinder in-line, V6, V8, V12 and V16) variations (the 92 is basically the same engine as the 71 - and even shares many parts - the difference being that the cylinder volume for the 92 has been upped to 92 CI from the original 71 CI - hence the names for these series) have had such a long production (starting prior to WWII and ending in the late 80's) life... They have been used in automotive (trucks, busses), industrial (generators, equipment) and marine (auxiliary and main engines) applications for roughly 5 decades!!! The 6 and 8 cylinder in-lines are basically doubled up 3 and 4 cylinder units... Similarly, the V6 and V8 versions are doubled up versions of the 3 and 4 in-line units in a V configuration... The V12 and V16 are basically doubled up V6 and V8 units...

In fact, the main reason as to why they were discontinued is due to the fact that it became uneconomical to adapt them to the newer EPA requirements... If the government hadn't come up with those regulations they would probably still be manufactured... The US Navy still uses them in certain applications!... Just one of the reasons why you can still buy a COMPLETE factory rebuild unit...

There's one thing you should know, while parts for "standard" 71/92 series DD's are still quite common for all versions (NA, T, TI) the exception is that it's getting very hard to find some parts for the last versions (DDEC - Detroit Diesel Electronic Control)... Specifically pistons (their pistons are different), turbos (also different) and anything to do with the electronic controls... I expect this to get worse over time...

Mechanics: due to its popularity it's not hard to find mechanics that are very experienced with these engines... Again, the DDEC version is the exception to the rule... This being due to their relative rarity as well as the fact that to properly work on these engines one needs a laptop with the proper software and cables (in order to "talk" with the ECM)...

I wouldn't consider anything less then liners, pistons AND connecting rod bearings as a "full" overhaul (aside from head jobs, injector rebuilding and turbo rebuilding)... This would usually be done "in frame" (i.e. without taking out the engines)... Of course, a really "full" overhaul would also include the crankshaft's main bearings... But that can only be done when the engine is hauled out... And, once the engines are hauled out there's little difference in terms of labor between an overhaul and a full rebuild... Several DD specialists (they did nothing else in the Israeli navy) told me that all things being equal (which they're never) and assuming "by the book" maintenance a 71/92 series should see it's 1st overhaul at around 2K hours (give or take 10%)... You can get away with doing this "in-frame"... By the time you get to the 2nd overhaul (around 4K hours) you'll also have to do the main bearings... That means taking out the engines... 3rd overhaul at around 6K hours would be a repeat of the 1st one (i.e. "in-frame")... By the time you get to the 4th overhaul at around 8K hours you're really looking at a complete rebuild... A complete rebuild would include new crankshaft, new camshafts, ultrasonic examination of timing gears and so forth...

[Navatech]

Frankly, if it were me I'd be looking at a pre-overhaul boat and, at that stage, I would consider repowering with lighter and more efficient engines... As this is for an older boat your new engines can be newer engines (i.e. rebuilds) which don't meet the latest EPA regulations (you're exempted when rebuilding/repowering an older boat)...

If you do decide going for one of the post "overhaul" boats I strongly suggest getting a DD mechanic to do an engine survey... And I mean a COMPLETE engine survey... Oil analysis, compression on ALL holes etc... Start out by getting their receipts for the parts... "Reliabuilt" is the trademark for (DD) factory rebuild parts...

Keep in mind that it's only natural for people to seek the cheapest possible route... Especially if they know they're going to sell the boat... Just in case anybody needs reminding, cheap and engine overhauling/rebuilding are contradictory terms!!!

[IRGuy]

I have been told that you can hang a picture of a Detroit engine on a wall, and when you come back the next day there will be oil on the floor.

As an old timer told me.. World War Two was won on Detroit engines.

[Rawleigh]

Every landing craft and small boat in WWII had them in it!

[STraenkle]

Where's Thudddd when you need him?

[mike ohlstein]

Where ever he is, he's driving something that is powered by an International 444......(Ford 7.3).

[MarkD]

Speaking of missing persons, where has Lico been? Anybody know if he is OK?

[Tooeez]

About 15 years ago I worked for a municipality that had four boats each powered with a pair of 12-71 DDEC's rated at 900hp. These boats were run hard, and all went about 7,000 hours before the first overhaul. But, you needed a tech with a laptop in order to do any maintenance.

[Navatech]

But, you needed a tech with a laptop in order to do any maintenance.

A PC, some special cables for the connection AND some custom DD software which, AFAIK, is incompatible with modern versions of the Windows OS...