Am I crazy to buy a boat with 30 year old DD 6V92s?

I have made an offer on a boat powered with the original pair of 550 HP 6v92 Detroit Diesels. Both have been rebuilt in the last few years and they have all the documentation on the rebuilds. I wouldn't buy the boat if i thought I'd have to re-power her in the next 5 years. Please let me nknow your thoughts and don't hold back.

Capt. Kirk said:

I have made an offer on a boat powered with the original pair of 550 HP 6v92 Detroit Diesels. Both have been rebuilt in the last few years and they have all the documentation on the rebuilds. I wouldn't buy the boat if i thought I'd have to re-power her in the next 5 years. Please let me nknow your thoughts and don't hold back.

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I am the fairly new owner of a boat with a pair of 25 year old DDs 8v92TA.

By the time I closed on the purchase one engine had been completely rebuilt as a result of a failure on my Sea Trial and both engines had their entire cooling system removed/cleaned/rebuilt.

These engines have sleeved cylinders so age is of little importance really. If they were rebuilt they should have had cylinder sleeves and pistons replaced.
If they check out OK at sea trial, temps and pressures OK at WOT and you have a good mech do an engine inspection during sea trial you should be OK.

I've been running DDs for almost 60 years. While I prefer the 71s, 92s are good engines and (IMP) better than most yacht engines sold today or yesterday. If you learn the maintenance, keep the oil clean, they should last many years.
The engines are mechanical, no sensors, no electronic injector control, so they're reliable. The more you learn to do yourself, the better the engines will run. Stay away from the average marina mechanics. Most have no idea how the engines work.

No, you aren’t crazy. We had Detroits in a previous boat and they ran and ran. Leak oil and are noisy but they run forever. Hopefully they have something like Airseps on them, if not get Airseps or the Racor system. It will save a lot of cleaning the engine room. Good luck!!!

Capt. Kirk said:

I have made an offer on a boat powered with the original pair of 550 HP 6v92 Detroit Diesels. I wouldn't buy the boat if i thought I'd have to re-power her in the next 5 years.

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You should never have to repower as those engines can be easily rebuilt in place in the vast majority of cases. My last boat had 892's, from which J&T squeezed 790 hp = 1.07 hp per cubic inch. As a result, near full throttle they were moments away from imploding -- all it took was some obstruction in the raw water intake and they would quickly overheat. And my aluminum heads would crack. At 1 hp per CI, yours is exactly at the threshold where conventional wisdom held reliability would suffer at any more horsepower.

When I still had that boat, I considered DD's reputation for leaking lots of oil to be grossly overstated. With my current boat, equipped with Cummins QSM 11s, there is absolutely zero oil leak anywhere, so by comparison I guess the reputation is somewhat deserved. The really great thing about these DDs is there are so many in service around the world, parts and mechanics are abundant. Moreover, they are very simple engines -- no computer, no common rail, and being two stroke, they have exhaust valves but no intake valves. Lastly, and this is a bit of an acquired taste, but nothing beats the sound (really a rumble) - or smell - of two strokes. Some tournament billfish guys believe that sound raises fish.

I would go into West Marine and buy all the oil absorbent pads they had in stock. Then go and cover the engine room decks with the pads. Change them out frequently and it helped contain the oil. Most of the oil came from the air boxes and was blown throughout the engine room. The mechanic fixed some home made Airseps that were cheap and worked great. After a couple of thorough cleanings the engine room was pretty clean. Then I just put the pads directly under the engines and all was good. And yes, the exhaust sounded awesome.

Capt. Kirk said:

I have made an offer on a boat powered with the original pair of 550 HP 6v92 Detroit Diesels. Both have been rebuilt in the last few years and they have all the documentation on the rebuilds. I wouldn't buy the boat if i thought I'd have to re-power her in the next 5 years. Please let me nknow your thoughts and don't hold back.

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I can hear DDs as they pass by my home. Wallace Island is 1 nm away. On the far side of Wallace is Trincomali Channel. I can hear DDs as they head up TC, until the sound is obscured by Wallace. Distinctive, loud. Could be hard to adjust to that level of noise as a full time feature of your boat.

Actually on our previous boat with Detroits the sound at the helm or flybridge didn’t seem objectionable. I think most of the noise exited out the transom and went astern.

My blessed John Deere has never blown oil.

markpierce said:

My blessed John Deere has never blown oil.

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Was it designed 70+ years ago??? Apples and oranges.

Comodave said:

Was it designed 70+ years ago??? Apples and oranges.

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Nope.

I sometimes cruise on a vessel with twin 16v92s. The rumble effect is minimal and pleasing. Oil messes are easily kept in check. Good mechanics with deep DD experience however are harder to find as retirements occur. Treasure the gray beards.

sunchaser said:

Treasure the gray beards.

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Now there's a phrase. I like that!

Greetings,
Mr. CK. It hasn't been said yet but you're crazy to buy a boat...

550hp out of a 692 is the top rating for the mechanical version. They were used in lots of sporties and cruisers that needed that much hp to plane. That engine, when run hard, did not last very long. Piston rings and liners might get 1500-2500hrs.

BUUUT.. That very same engine if run at hull speed and like 1000-1200rpm could last many thousands of hours. So even if rated for 550hp, if you run it at say 100hp, it will last, without doing anything but keeping out of the throttles.

So whether to recommend these depends on how you intend to use the boat.

"So whether to recommend these depends on how you intend to use the boat."

And how the boat was used in the past.

Detroits mistake was in the sealants used to assemble the engine.
Use DD stuff it will leak unless very fine workmanship was used. Clean surfaces and a torque wrench.

Using OTS sealant was common for bus companies , that rebuilt their own engines.

At modest low output the DD are almost a forever engine.

Comodave said:

No, you aren’t crazy. We had Detroits in a previous boat and they ran and ran. Leak oil and are noisy but they run forever. Hopefully they have something like Airseps on them, if not get Airseps or the Racor system. It will save a lot of cleaning the engine room. Good luck!!!

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I had a 54' sport fisher with DDEC 8V92s (760hp each) that was a terrific boat. As mentioned above, the engines did leak oil but a pair of Airseps from Walker Engineering solved the problem, so much that I carpeted the center aisle (red outdoor carpet) and enjoyed eating my lunch in the ER next to those big chrome plated valve covers! Great engines!!

Comodave said:

I would go into West Marine and buy all the oil absorbent pads they had in stock. Then go and cover the engine room decks with the pads. Change them out frequently and it helped contain the oil. Most of the oil came from the air boxes and was blown throughout the engine room. The mechanic fixed some home made Airseps that were cheap and worked great. After a couple of thorough cleanings the engine room was pretty clean. Then I just put the pads directly under the engines and all was good. And yes, the exhaust sounded awesome.

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This boat has Walker Airseps already, which will help minimize the mess in the engine room, although I’m hoping not to eat my lunch down there too often. It does look like it could use a good cleaning now. She also has dual Racors on both engines and single Racors on each genset, fuel polishing and an oil change system, which I am happy to have.

Detroits mistake was in the sealants used to assemble the engine.
Use DD stuff it will leak unless very fine workmanship was used. Clean surfaces and a torque wrench.

Using OTS sealant was common for bus companies , that rebuilt their own engines.

I don't really understand what this means. Can you please elaborate?

I have received conflicting feedback on how to best run the 6V92s.

Some people have said, “you can’t baby these girls, you got to run them on the pins.” I take it that means at higher RPMs.
This is not my inclination.
Others here have said:
“That engine, when run hard, did not last very long. Piston rings and liners might get 1500-2500hrs.
BUUUT.. That very same engine if run at hull speed and like 1000-1200rpm could last many thousands of hours. So even if rated for 550hp, if you run it at say 100hp, it will last, without doing anything but keeping out of the throttles.”
“At modest low output the DD are almost a forever engine.”
I plan to cruise the boat at low RPM at 8 or 9 knots which I expect qualifies as, “modest low output.” Running her this way, I assume I will need to run up her RPMs to blow out the carbon at the end of a long day.
The owner says he ran the boat, “at 8 to 10 knots, occasionally 20 knots.”

Please let me know if you agree with that these engines should last a long, long time if run modestly.

Havingnthe Walkers will certainly make it much easier to keep the engine room cleaner. They should run forever if you stay out of the throttles.

Capt. Kirk said:

I have received conflicting feedback on how to best run the 6V92s.

Some people have said, “you can’t baby these girls, you got to run them on the pins.” I take it that means at higher RPMs.
This is not my inclination.
Others here have said:
“That engine, when run hard, did not last very long. Piston rings and liners might get 1500-2500hrs.
BUUUT.. That very same engine if run at hull speed and like 1000-1200rpm could last many thousands of hours. So even if rated for 550hp, if you run it at say 100hp, it will last, without doing anything but keeping out of the throttles.”
“At modest low output the DD are almost a forever engine.”
I plan to cruise the boat at low RPM at 8 or 9 knots which I expect qualifies as, “modest low output.” Running her this way, I assume I will need to run up her RPMs to blow out the carbon at the end of a long day.
The owner says he ran the boat, “at 8 to 10 knots, occasionally 20 knots.”

Please let me know if you agree with that these engines should last a long, long time if run modestly.

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Some of the older, low output DDs did like to be run towards the upper end of their RPM range, particularly in trucks where high RPM didn't necessarily mean full load. The higher output ones shouldn't be run like that. If run reasonably, they'll live a decent life. But if run flat out or close to it, they'll burn up just as fast as a pair of gassers being run like that.

Just keep them between 1200 and 1400 rpm , they will last forever. I like the 71's better, also prefer the mechanical injectors over the DDEC electronics. Just keep good oil and new antifreeze/ anticorrosion fluids in the block. If you have intercoolers (especially sea water cooled intercools) disassemble and renew the gaskets ever 5 years as a preventive maintenance program.

If they're in good condition now you should be able to keep them running for longer than it will be possible to keep you running. 1000 - 1200 rpm a little low IMO, go to 13-1400, combustion pressures high enough to seal the rings, avoid running much below 60% power, that will mean pushing it a little beyond hull speed. I think blowing out the carbon is snake oil, and a routine of it combined with chronic low power running should cause increased deposits in ring grooves increasing the risk of ring breakage. These engines were designed to spend most of their life producing 80% of rated power.

Different boat, different motors, but my friend with a 53 Hatteras DD 8V53s says the same - run it at 8-10 knots most of the time, run it at 15 knots every once in a while.

We have had boats with 6-71N, 6-71TI, 6V-92TA and 8V-92TA Detroit’s.

The 550hp 6V-92TA was in a 38, Blackfin SF. They made it to 3600 hours before rebuild in place. Running a MY can be similar to a SF in that you spend long hours at trolling speeds and then a few hours at higher cruise.

Here is how to get longer life out of your 6V-92TA:

Make sure that at full load, with all gear on board, full fuel and water, no waste, that your WOT rpms are 2350. This is imperative to have the propellers correctly loaded. Re-Prop if necessary to get this right.

Never cruise for extended times over 1950 rpm. Never.

Install pyrometers and run them correctly. You will find the Exhaust Gas Temp specs in your manuals, they will be in a range, do not run it past that range and generally keep them in the middle.

If your are running all day at 8 - 12 knots you should blow them out by running up to 1850 - 1950 rpm for 15 or 30 minutes before entering the harbor.

You have to find the right spot for low cruise, you do not want to be on the edge of where the Turbo kicks on and off. Avoid that range at all costs, cruise below it or above it but never on that spot. It varies on sea state and load, pyrometers will help you here.

Perform oil changes religiously, never more than 200 hours apart.

Get the best fuel filter system in place you can but. Multi-stage 5 microns before the engine.

Spare hoses and fittings onboard, plus always carry 5 gallons of diesel in a jug. Necessary for priming filters if you go through a bad batch of fuel and clog the system.

Walker or Racor Airseps are mandatory.

Happy boating!

1994 DD 6v92TA

I don't notice the engine noise while motoring. It's just a part of boating. We've had our boat 7 years and have had no major issues. And our engine room stays clean with just a few pads under the engines.

If you can put up with the noise, and don't mind a few oil drips, buy the boat.

There are a lot of wives tales on how to run them. Some say on the pins to keep them hot and clean, others say under 1200 rpm and they last forever.

We have 8v-92 TA's in ours. I let them warm up at the dock, then head out for the day/week. Its a 1978, but the engines have been rebuilt and now have 500 or so hours on them.

I don't run it on the pins, I don't chug it along. Mostly at 10-16knots
Change the Oil, and change the fuel filters. I do oil changes at 100 hours, and all fuel filters. DD run a lot of fuel through the system, and return a lot of it back to the tanks, its like a built in fuel polishing pump!

Carry extra oil, as they use oil.
Carry extra fuel in a jug as mentioned above.
DD hold a lot of oil, I pack 7 extra gallons and a filter set, this is enough for one engine. I also pack a full set of extra Fuel filters for the boat.

Pack an extra sea impeller, and the proper tool's to change one out.
Carry the right oil, DD like straight 40 weight low ash.

You are not crazy but you need to move cautiously regarding those rebuilds.

pete

Had a 48 Hatt with 6/92TA, ran at 1400 rpm which gave me 10kts. Ran them up before shutdown, had walker air seps and resealed a few spots and no no oil leaks or messy bilge. 3000 hrs in 12 years. Loved my DD’s