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Old 04-22-2021, 03:54 PM   #1
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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.
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Old 04-22-2021, 04:01 PM   #2
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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.
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.
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Old 04-22-2021, 04:36 PM   #3
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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.
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Old 04-22-2021, 04:42 PM   #4
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No, you arenít 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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Old 04-22-2021, 04:43 PM   #5
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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.
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.
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Old 04-22-2021, 04:48 PM   #6
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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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Old 04-22-2021, 07:13 PM   #7
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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.
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.
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Old 04-22-2021, 08:36 PM   #8
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Actually on our previous boat with Detroits the sound at the helm or flybridge didnít seem objectionable. I think most of the noise exited out the transom and went astern.
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Old 04-22-2021, 09:08 PM   #9
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My blessed John Deere has never blown oil.
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Old 04-22-2021, 10:54 PM   #10
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My blessed John Deere has never blown oil.
Was it designed 70+ years ago??? Apples and oranges.
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Old 04-22-2021, 10:59 PM   #11
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Was it designed 70+ years ago??? Apples and oranges.
Nope.
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Old 04-23-2021, 06:04 AM   #12
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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.
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Old 04-23-2021, 07:21 AM   #13
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Treasure the gray beards.
Now there's a phrase. I like that!
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Old 04-23-2021, 07:31 AM   #14
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Greetings,
Mr. CK. It hasn't been said yet but you're crazy to buy a boat...


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Old 04-23-2021, 10:39 AM   #15
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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.
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Old 04-25-2021, 06:59 AM   #16
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"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.
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Old 04-25-2021, 08:33 AM   #17
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No, you arenít 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!!!
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!!
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Old 04-25-2021, 09:49 PM   #18
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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.
This boat has Walker Airseps already, which will help minimize the mess in the engine room, although Iím 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.
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Old 04-25-2021, 10:17 PM   #19
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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?
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Old 04-25-2021, 10:29 PM   #20
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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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