Detroit diesel 8v92

Hi,

You might want to have a read of this article.

http://www.yachtsurvey.com/comparing_diesel_types.htm

Particularly this statement:

The 6-71, 6V92 and 8V92 perform well at reasonable horsepowers. For overall longevity, I'd opt for the 6-71 in any boat where the power range is applicable. Reliability is without parallel. In the hot rod class, I'll take the 6V92 at less than 550 hp while being prepared to follow the maintenance guide religiously. This is a spectacular little power plant for those that like to push the 30 knot envelope in a mid size boat.

The 8V92 would fall into the same category, except that the modifiers like JT, S&S and Covington try to squeeze too much power out of these blocks. A good deal at 735 hp and below. A poor choice above that.

A "late '80s" Ocean is mentioned.
In 1987, Roger Penske took over Detroit Diesel, and one of the first things he tackled was to put an end to the marinizing of Detroits by S&S, J&T, et al., in favor of what he called "box engines" or 'out of the box' from the Factory...no more oddities like aluminum exhaust manifolds(!) out of NJ or hyper HP motors out of TX.

Even percussive maintenance should get you to the 2000-hour mark.
There is an older 50 Hatteras with 8V-92s (charter boat) up in the Palm Beaches with over 5K hrs. on the original top ends.

Best advice is to avoid monkeying around with air/fuel balance by modifying what the Factory gave you. Instead, save that money for a set of kits (pistons/rings/liners) when the compression finally goes away.

Cheap and easy solution, you ask? 1900-1950 RPMs is what those motors like.

Actually closer to 1950rpms or even 2000 rpms. The reason the 92's series lives a shorter life then the 71's is because of too much fuel and injectors that are too large. The fuel doesn't get metered properly under 1900 rpms (and above hull speeds) and the cylinder walls get washed out by the additional fuel and not lubricated well enough by the oil. Also change the coolant every 2 years as directed to keep the o=rings happy (another 92 series issues). A friend of mine had a Viking with those and he was meticulous about maintanence. He owned the viking for over 20 years. He'd see around 2,000 hours out of them between overhauls.

Hi,

One thing you need to ask yourself here is how many hours a year are you going to clock up?

If you were to remove the turbos and de rate the engines you will find that there are quite a few dollars in making the changes to the exhaust and air system you will need to make, the changing of injectors is probably the smallest issue to doing this.

You will also have to consider the changes to performance and possible resale implications that de rating the engines will bring.

You don't want to do this. If you de-prop the boat, the engines at 1950 rpms will be running a much lower load factor then with the proper props. Meaning- they will get fuel metered for 80% load, and only seeing 60% load for example and running more fuel rich.

You can put smaller injectors and leave the turbo's and exhaust the same on a DD, the rack and injector pump has to be adjusted as well. I ran a 58' Hatteras YF with 8v71 TI's and this is precisely what the factory DD dealer did when they did majors on them. Talk to a DD dealer and ask them about detuning them with a smaller injector. Most 8v92's have 140 LPH(liters per hour) injectors, you could probably move down to the 110 LPH injectors. You will also have to take a little pitch out of the props so you still achieve 2350 rpm's. I found that on the Hatteras, it lost 1.5 knots at cruise, it burned 30gph at cruise versus 45 gph, and it ran very very clean at hull speeds and very clean and crisp throughout the rpm band.

Hi,

I do not recall the good old two stroke Detroit Diesel having an Injector pump as such.

Each Injector is a pump on one of these engines. So if you change the injectors you are changing all the injector pumps.

actually, you're right I had a brain fart this morning. They only have a fuel pump and the injectors on DD's act as the injector pump. So just the rack needs to be adjusted and possibly the injector timing (which is what I meant to say) to a different setting. A lot of the companies changed the injector size and timing from the intial specs when they marinized them depending on what they were trying to achieve with them, such as Johnson Towers looking for more HP and Covington looking for more torque instead of HP. The Covington 12v71's in the 75' Hatteras I run use a unique setting that is for a generator, that you have to argue with any dealer setting the rack because it's not a marine setting and they insist on using the marine setting which causes the boat to black smoke like it has dead cylinders. After they did an engine survey, it took 7 seatrials to get it back to the right injector timing, which they kept insisting on not using.

Anyways, call a good factory detroit diesel dealer and they should be able to tell you all of the specifics. I just know it can be done and it was done on one of the yachts I ran for several years and it's still running around without any issues since they were rebuilt and swapped around in 2001.

Also exhaust gas temp gauges are a good addition to any boat running 92 series, and will tell you how rich/lean they're running in your particular boat and the ideal cruise rpm. If I remember correctly, you want the EGT around 850 degrees at cruise (double check this with the dealer also as it's been a while), it may be 800 degrees.

Yes, but no. The entire issue with the 92 series is with the injectors being so large that they don't meter the fuel properly or have a good spray pattern at lower loads. Boats that run at cruise speed all of the time, lasted better. So taking pitch out of the props would lower the load factor at a given RPM and increase the problem of the fuel injectors metering properly at lower loads. Johnson and Towers added even larger injectors then the factory usually on the 92 series and made the problem even worse........I was told the 6v92 J+T's have to rebuilt every 200 hours by a FDDA rep.

Okay X-V-92 people: what applications are typically considered better with a 83% (bypass) blower? Now name some for the 100% (non bypass) blowers? Yes I understand but wish to hear other opinions that I may not have considered. Have you driven a vessel that needed the version it did not have and if so what were your thoughts? During a rebuild did you change versions and if so quantify the changes that manifest themselves post rebuild.
Thanks
William

Would you be able to translate that into something the normal reader header here can understand?

That lever thingy with the red ball might be the best way. Just don't push it forward so much for so long.

I was going to say the same thing. I have had great luck with Detroits and currently have 8V92's that run flawlessly and don't smoke.
I like set my boats up slightly underpropped since as other posters here have also said overloading and running them too hard seems to be the real problem.
Personally, I think modifying the design of the engine in pursuit of "reliability" seldom turns out well.

I would maintain 'em, underprop 'em, and drive'em easy.

8v92's on Liveaboard

I'm going to look at a 50 plus older yacht that has a pair of 8v92 turbo engines onboard. To my knowledge at this point they crank up and run just fine. But I get the distinct impression that this vessel has not had a lot of running time in her lifetime, having been used as a part time liveaboard by an early owner, and not having been run a great deal by her current owner. So I have a number of questions to ask about these particular engines, their environment, and their 'feeding'.

First off let me offer up that I am also looking at this vessel as a 'liveaboard potential vessel'. I would likely not be moving her more than 2-3 times per year for relatively short distances, and then possible one long trip down the inter-coastal sometime in the next two years.

A few initial questions:
1) What concerns should I have to consider about the limited use of these engines may have had over their past 30 year life?

2) What concerns must I have about the age of the fuel that may be onboard? I know I need to look closely at the fuel filter systems that are onboard, and their capabilities to filter older fuel that might well be contaminated and/or microbes organisms.

3) Do I definitely need to plan on running any & all of fuel thru some sort of polishing system?

4) If I were making one sample move of a couple hundred miles, would it be reasonable to do this at a 'high idle speed' rather than fully planning out....in the interest of lowest fuel usage?? How hard on those engines is extensive idling?

5) Is this 92 series noted for less stellar durabilty...or more susceptibility to maintenance requirements than other GM two cycle diesels?

6) What other care & 'feeding' of these engines might someone suggest to maintain them in good condition even while being utilized very little?