New skipper, advice please on a 1989 Marine Trader, Det D's/J&T 6-71TA's....

Hey all, looking to purchase a 62' boat here, kept in boat house all it's life and roughly 4500 engine hours, well serviced by a full time USCG licensed skipper and want to get some advice/suggestions/experience with this make and this engine. It's a Marine Trader Med Yachts make, and I am a cruiser kind of skipper, 10 knots is fine. I am not looking to do major blue water, mostly Puget sound and inner passage stuff. I am also seeking to live on board when retiring.
Boat also has fuel polishing, twin North lights gen sets, low hours and appears in great shape.
My question to the audience, anyone with a Marine Trader of 1988-1991 era, how are they holding up? DD's by J&T thoughts? Parts appear easy to get and cheap. I hope to hear the good/bad and things to look for. Will go to survey in 2-3 weeks and feel the boat is fairly priced. Owners have operated with an open checkbook, according to the captain who is not the owner.
Thanks folks and any/all input is appreciated. Anyone else up near Everett, WA where I will be docked?
James

Good luck with this. Not familiar with this boat in particular, but have been doing a LOT of reading as I am too in the hunt.

The "genre" of id to late 20th century Asian built boats shares a few points to look for, although these points can apply to boats made anywhere. Make sure your surveyors (yes two, more on that later) know what he's doing.

* Water intrusion into the laminate with resulting de-lamination, ESPECIALLY when there are teak decks installed with their associated 3000 screws.

* Steel tanks, if installed. The leaks mentioned above get water on top of the tanks, which then rust out. Their removal is often a huge job. Replacements are also pricey.

* Electrical wiring. Non-tinned wire, corrosion.

* Leaking windows, see the first point.

*The DD 6-71, with proper care, feeding and regular but not over strenuous exercise will last a looooong time (10,000 hours is not unheard of). It is a sleeved engine, and can be rebuilt in situ. Unless something really catastrophic happens the block itself will last forever. Get a GOOD DD mechanic to do the engine survey. Insist on oil and coolant analysis. If you can get the parties to agree do a compression check. More money, but peace of mind.

INSIST that the engines are not run for at least 48 hours before the engine survey. The mechanic HAS to hear a true cold start. Check the temps (invest in an IR temp gun) when you arrive on the scene. If they have some BS story about "had to move the boat" or something, cancel the engine survey.

Insist on a sea trial.

These are the biggies.

Good luck.

4500 hours on a J&T DD is a BUNCH. 6-71 NAs will run 10,000 hours but not the jacked up J$Ts. Factor in an inframe rebuild with your offer. If its been undercover its whole life you wont see the evidence of leaks so much,,, it has them. What gears does it have ? Gear ratio ? Shaft size ? Lots of things to look at !!!

As a newbie, I don't totally understand what the J&T upgrades do or what an "inframe Rebuild" consists of? So anything you can elaborate on this would be most helpful. From what I read, the Detroits are simple/good engines at low RPM's, correct?
Thanks again.

Not sure where the "jacked up" part comes from in a J&T. AFAIK they rebuild to factory specs. Am I missing something?

Yes, DD's are simple low RPM engines. If you maintain them and run them at low RPM.

The term "inframe rebuild" is more applicable to the trucking world, but the principle is the same. Pull the heads, replace. Pull the oil pan, remove the rod caps pull all the pistons, rods. Pull the sleeves. Replace sleeves, rings, bearings.

Over simplified, but about it.

Det D's/J&T 6-71TA's....

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I think (I don't really know) that the turbo and aftercooling was where the "jacked up" came from. If these 6-71's are putting out over 400HP each then I think 4500 hrs is a lot. Again...I don't "know".

DDs are anything but simple. They are much more complicated in design than a 4 stroke diesel. Much more moving parts and more application specific designs than most other makes. The 6-71 can be had from 165 hp up to 485 hp, all on the same standard block, mostly. J$T was famous for squeezing a BUNCH of hp from just about any DD. A J$T 6-71 at 485 hp generally will only last 3000 hours, if well cared for. Of course, how it was operated is a factor. That same engine ran at low power is usually a stinking, smoking pig that needs to be spun up every so often. However, at 210 hp with N50 injectors and no turbo it will happily run at 1250 rpm for years on end. Different compression ratio, cam timing, port height, etc. There are so many configurations for these engines that it boggles the mind. And, its getting really hard to find old school DD mechanics that actually know them. An "inframe rebuild" is simply new pistons, rings, liners and rod bearings. Have the heads checked and turbos looked at. You WILL find lots of exhaust problems, so plan on all new risers and blankets if dry turbos. Wet turbos and there corresponding manifolds have there own problems. You REALLY need to know exactly what engines it has.

Ah, missed the turbo part. Yes, cranking that many horses out will come at a price.

We moor in Everett and it has a lot of rain. So if the boat been under cover, I would require the boat be moored out in open cold and rain for a period of time. Unless you are planning to moor it under cover.

The DD 671 is a one of the longest lasting long proven history and parts service is readily available. However the J&T add turbo and over sized injectors which increases the horse power and RPM which tends to shorten the live. What shorten kills most engines is not the engine but what hangs off them and increasing the HP & RPM. So check the maintenance and it's present condition. One quick way is make sure they start the engines COLD, and listen how hard they start and watch what comes out of the exhaust. Phil, Everett Marine Service is my mechanic, who I recommend. A 671 can be rebuilt in place, rather than having to replace and/or taking it out of the boat. Which when it comes time to rebuild is cheaper and easier.

Anyway make sure you use a surveyor not recommended by the broker owner.

Kulas44, thanks so much for all the tremendous insight to this newbie. The engines are 485 hp, 6V71TA's with 4500 hours and run almost exclusively at 1650 rpms and 11 knots. Max speed according the the USCG captain is 15 knots. They have been well cared for. Here is the quotes from the captain.
11 KTS -------- 1650 rpm
15 KTS --------- Dont remeber we always run at 11 kts. The boat just seems alot happier there

Oil Burn
It depends mostly on the tide and the sea condition. Average would be about 1 - 2 qts every 100 hours. WE have had weeks of running with no oil burn.

Last what I would call major maint. would be last year we pulled the port blower and had it rebuilt. It was working fine except for the seals were leaking.

All injectors and lines were replaced about 2 years ago.
Any and all comments are welcome here.
Thanks everyone....

Phil, thanks so much..will be mooring up next to you this spring if all goes through. The north part of Everett has some slips open...was up there for 20 years before moving to CA and selling my boat, but miss the NW boating, crabbing, San Juans, etc.

Phil, any guess on what a rebuild would run for the engine I am talking about? I see a bunch of rebuild kits Ebay and other places for a reasonable amount.

You need to find a Detroit 2 stroke specialist to give those engines a very thorough survey. What some guy may say, and reality over those 4500 hours could well be very different things. Just about any moron with some sea time can get a USCG ticket so don't give any credence to that. Caveat Emptor!

To rebuild a turbo Detroit correctly by the right person, figure 3,000 a cylinder. You'll have a literally new engine, but the mechanic is the whole game. Then you have the transmissions.....

Capn James Brett said:

Phil, thanks so much..will be mooring up next to you this spring if all goes through. The north part of Everett has some slips open...was up there for 20 years before moving to CA and selling my boat, but miss the NW boating, crabbing, San Juans, etc.

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Where is the boat presently moored. The north marina is all open so make sure its PNW rain winter ready. We are moored on the commercial dock south marina. Everett has a 75 ton lift and a well service parts and yard. The water is brackish which is easier on the boat than the salt.

Capn James Brett said:

Phil, any guess on what a rebuild would run for the engine I am talking about? I see a bunch of rebuild kits Ebay and other places for a reasonable amount.

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As mentioned its the mechanic not the parts that is important. Parts are readily available.
I don't know what it would cost.

Phil Fill said:

Where is the boat presently moored. The north marina is all open so make sure its PNW rain winter ready. We are moored on the commercial dock south marina. Everett has a 75 ton lift and a well service parts and yard. The water is brackish which is easier on the boat than the salt.

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Phi, presently down in Texas and has been under a boat house cover all it's life. Teak decks and that is what scares me about Everett....rain, rain, rain. Will look forward to meeting you this spring. Thanks again.

I would "think" that a pair of 210 hp NA DDs would be a very much better engine for the way the boat has been operated. The 485s have a lot of extra and expensive equipment that is not being utilized. Turbos, big raw water pumps, big (sloppy) injectors, etc. If it were me ,as I said previously, I would subtract from the asking price for the rebuilds then have them done to 210 hp specs. Simple enough, just different pistons and liners. Same price. Leave off the turbos and reconfigure the exhaust. Resetting the cam timing would be an additional expense but neccessary. You would need to remove the bellhousing adapter to access the gear train. It probably has Allison gears, which are really good and easy/cheap (relatively) to work on. TwinDisk are also good and J$T used them a lot. Not so cheap/easy as Allisons. At any rate the gears would need to be removed to replace the rear crankshaft seal. I would NOT buy a boat with 485hp 6-71s with 4500 hours on them unless it was priced appropriately. A complete inframe usually runs about $3000 per hole, so $18000 per engine is $36000. Much cheaper than a total repower at about $60,000. Any good DD mech. will tell you that those 485s dont have much (if any) life left. Do a lot of research before pulling this trigger.

I run J&T 6-71TI s in my Viking 450hp.
Listen to Kulas he's correct. I also am extremely skeptical about the reported oil consumption reports you were given. Try about 1qt for every 10 hrs at 1900rpm.

Oil Burn
It depends mostly on the tide and the sea condition. Average would be about 1 - 2 qts every 100 hours. WE have had weeks of running with no oil burn.

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Scratching my head on this statement.....

DDs are anything but simple. They are much more complicated in design than a 4 stroke diesel.

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Heck no. They are the large diesel equivalent of a lawn mower engine. What makes them so more complicated?

Capn James Brett said:

Phil, any guess on what a rebuild would run for the engine I am talking about? I see a bunch of rebuild kits Ebay and other places for a reasonable amount.

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Just had a DD J&T in frame rebuild by Detroit Diesel. Cost was $15k and took one week. Labor was about $8-9 of the total. Great motors, don't run them hot and they will last a very long time. Just remember - if they aren't leaking oil something's wrong!

Just because its called a two stroke does not in any way make it even remotely similar to a simple 2 stroke lawn mower engine. How about 3 push rods per cylinder, 4 valves per cylinder, a variable injector per cylinder, operated by a pushrod from a roller lifter integral to the cylinder head, as are the 2 pushrods for the 4 valves, all built into the head. Then the blower, that is driven by the camshaft gear train thats behind the bellhousing adapter, and the govenor that is driven by the blower shaft, or a seperate gear off the cam train depending on how its configured. Then the mechanism for controlling all this, the rack, thats controlled by one of many types of govenors. The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm. Much, much more complicated, by far. Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated.

You have received some good advice. The engines may come through a survey just fine. If so you will have time to evaluate your replacement as well as rebuild options

Suggest you read the J&T 6-71 archives on boat diesel. You will be able to address questions to some very good DD people who frequent that site.

Blindhog, thanks. Which model engines= did you have this done on?

Guys, thanks for all the help and great suggestions. Much to think about. The boat is one I don't want to lose and have looked on the docks and YW ad nauseam. I like the idea of dropping the Turbo's and dropping the horse power so RPM's lower/higher? What does this do to fuel burn? Right now, captain states. boat burns 1.2 gallons/mile, so that's 10 gph if my math is correct? Does sound right guys?

"Yes, DD's are simple low RPM engines. If you maintain them and run them at low RPM."

DD are rated and can operate at 2100 , but unless you are a sport fish you will not like the fuel bill.

Between 1600 and 1800 they have Very long service life , assuming 2 stroke not 4 stroke oil is used.

J&T do "hop up" the engines and running them for long hours at the higher 2400 J&T rating will shorten the service life.

The "sports" consider 1000 hour life a good deal.

Having the hop up goodies will not shorten the service life IF the engine is operated and loaded as a cruiser.

Basically the engine will burn a certain amount of fuel in its lifetime , the burn RATE is up to the opertator.

"The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm."


Yes the exhaust valves are moving 2x as often as is the injection the difference is each stroke is a POWER stroke , no wasted effort of an exhaust stroke .

The valves have a great service life as the scavenging blower cools them asa does their time seated.

But they have been doing this since 1936 with no effort.

"Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated."

This is the VIRTUE of the motor for end users.

Almost any configuration can be arranged , twins with the service items on ship center line , but turning in opposite directions , just ask, no problem, no added expense.

While the configurations can run probably to 50 variants ,
after its assembled its just a Jimmy , simple and cheap to keep like 10,000,000 others.

The Captain says "always run at 11 knots." For a 62 foot vessel that seems about 10 to 15 % faster than an efficient cruising speed thus putting the engines into a higher HP fuel burn zone and shortening their life. Heed Kulas's advice.

Dont get me wrong, I love the old DDs. I also know there biggest weekness is being "jacked up" by J&T and Covington, and in the later years even by the DD boys themselves. Its my opinion, and that of most others that know DDs, that the 485 hp 6-71 is the shortest lived of all. Even if ran conservatively. And, no matter what the captain says there is no way you can really know how this boat was operated. Another thing to look at is that these engines are totally inappropriate for a 62 foot boat. 12v71 NAs would have been about right. A lot of folks here are going to say the hp rating makes no difference, its how they were operated that matters. To some extent, and on most engines they are correct. The 485 DD has a BIG turbo, BIG injectors, BIG aftercooler, overdriven blower, BIG raw water pump, LOW compression ratio, etc. At low power levels it is way overcooled, even when the temp gauge says 180 the cylinder temps are to low for good combustion. Hence the need to "blow them out" occasionally. These engines purpose in life was to go fast for a short time. 2500 hours is the max between rebuilds. Read Pasco's thoughts on marine diesel engines, particularly the DDs, you'll enjoy it.

Capn James Brett said:

Phi, presently down in Texas and has been under a boat house cover all it's life. Teak decks and that is what scares me about Everett....rain, rain, rain. Will look forward to meeting you this spring. Thanks again.

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We presently are at South Padre TX with the land yatch. We are heading north Dec 28th to fly out of Dallas Jan 7, so we have two weeks to kill. That's a hint.

The Eagle has teak decks, however every year they have to be maintained, sealed, and covered from October to June. The back and Portuguese bridge is canvas covered so both area are usable area all year. The back deck is varnished and heated. The front deck is covered with a thick heavy white tarp where we store some of the summer stuff. So make sure the teak decks are maintained, rain proof and covered.

So how do you plan on transporting the boat to Everett and why. We are thinking of moving South for the winter, and keep the boat in the PNW for the summer. There are many boats for sale in the PNW? The Seattle boat show is the last week in January.

Have you considered the cost of getting this boat home.

Capn James Brett said:

Phi, presently down in Texas and has been under a boat house cover all it's life. Teak decks and that is what scares me about Everett....rain, rain, rain. Will look forward to meeting you this spring. Thanks again.

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The cost of getting this boat the west coast will be considerable. On the face of it the boat sounds overpowered, however once in a large sea state having reserve power for climbing large waves is an asset. On a boat of this size engines is just the begining of expensive systems, especially if you plan on a delivery on its bottom up the west coast. There are a number of Hatteras 58' lrcs on the west coast already that might suit your needs as well that have proven durability.

kulas44 said:

Just because its called a two stroke does not in any way make it even remotely similar to a simple 2 stroke lawn mower engine. How about 3 push rods per cylinder, 4 valves per cylinder, a variable injector per cylinder, operated by a pushrod from a roller lifter integral to the cylinder head, as are the 2 pushrods for the 4 valves, all built into the head. Then the blower, that is driven by the camshaft gear train thats behind the bellhousing adapter, and the govenor that is driven by the blower shaft, or a seperate gear off the cam train depending on how its configured. Then the mechanism for controlling all this, the rack, thats controlled by one of many types of govenors. The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm. Much, much more complicated, by far. Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated.

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My comments were TIC. I know how the DD's work, and am well aware that the only thing it shares with a lawn mower is that every down stroke is a power stroke and that they have intake ports instead of valves. I know about the rack, the blower, the N30's etc etc. And yes, there are endless configurations. But, that's for the designers to worry about. When you buy a boat those decisions are made. And I still maintain that they are pretty straight forward mechanical engines. Yes, you have to learn how to adjust the rack, injection timing and the governor, but it's all straight forward. Everything, including a complete rebuild in situ, can be accomplished with simple hand tools. No ECM (until you get to the DDEC's) no sensors, no software, and thus no "bugs". In fact, once it's running you can rip every wire off the thing and it will keep on running as long as it gets air and fuel.

And yes, hopping them up shortens their life. Like someone said, HP is ideal when it(they) move the boat just under hull speed somewhere in the 1600-1800 RPM range, and the whole thing truly runs at about 170ºF