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Confusion about engine specs

Discussion in 'Post Yacht' started by Blue Goose, Feb 7, 2015.

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  1. Blue Goose

    Blue Goose New Member

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    Hi Everyone,
    We are looking at an 82 Post SF. The broker lists the engines as DD 6-71 TI(s) rated at 410-hp. In researching the boat I see that the Powerboat Guide listed a 410-hp 6-71 option for the 42 SF in that model year but they don't specify an engine model; N, IT, TA, TI. However, when I attempt to research the engine itself, I can find nothing on a 6-71 TI rated at 410-hp. Everything I've been able to find related to the 6-71 TI for that model year rates it at 485-hp and it appears that the 485-hp engines were not offered in the 42 SF; only the 46. The 42 SF in 82 appears to have come standard with 6-71N(s) rated at 310-hp. I believe that the broker simply copied the information from the Powerboat Guide into his listing but before I begin to question the accuracy of the information he's presented I wanted to be sure of my facts. As an aside, when you run this boat on the NADA site the only engine option it allows you is the 6-71N(s) rated at 310-hp. Any additional information that anyone could provide would be greatly appreciated.
  2. RT46

    RT46 Senior Member

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    the 485 hp is the 671 TIB, it has a bypass. The TIB has different injectors, turbo, and a bypass blower.
    You can easily tell the TIB vs the TI because the TIB has the bypass assembly under the blower and air plumbing that goes into the inboard rear inspection port.
    Also the injectors and turbo are different, but you cant tell from looking at the engine.
  3. Blue Goose

    Blue Goose New Member

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    RT,
    Can you direct me to a technical source for information on this engine configuration? Other than people referencing the fact that they have them in their boats and ads selling boats with them installed, I have been unable to locate any source of information on these engines. I even tried a Google search on Detroit Diesel 6-71 TI 410-hp and was directed to multiple forums wherein people were asking questions about the engines, but not one single technical source. Thank you for your reply and the information you provided.
  4. RER

    RER Senior Member

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    The later era DD 6-71 came in a range of horsepower from 310NA to 385, 410, 415, 425, 450TI t0 485TIB.

    The 410hp DD 6-71TI is a great motor. Far more service life than the 485hpTIB. The 410's were common in the slant version.

    It is not uncommon for listings to have inaccurate specs. An inspection by a qualified DD mechanic would be your best technical source.
  5. PacBlue

    PacBlue Senior Member

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    Give Ed Tevis a call at J&T, I believe they were supplying the engines to Post at that time. He will have all the details and can potentially give you a copy of the factory sea trials if you can provide him with the engine serial numbers: http://www.johnsontowers.com/marine/reman

    The J&T 6-71 TI rated at 410hp is a good rating for this engine, much more reliable than the 450 or 485hp versions. Make sure you have the Walker Airseps to keep things a bit cleaner in the engine room. I would be concerned if the boat has Capitol Gear Boxes as they are no longer manufactured and service / parts is a challenge. Twin Disc or ZF is a better option.
  6. Capt Ralph

    Capt Ralph Senior Member

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    Find or get the serial numbers. Should be documented in a past survey I'm sure the broker has or can get. That's the key to a world of much information. Then tap on your favorite DDC shop. They can fill you in on all details of the original order and offer a factory part listing for those exact engine.
    J&T may have added some extra options but the DDC list will tell what was ordered and delivered. Probably who (whom?) they were delivered to.
  7. Blue Goose

    Blue Goose New Member

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    Thanks for the information and the referrals to other sources. According to the broker's write up there is a 2012 survey available. I'm trying to get ahead of the game by learning as much as possible before hand. The information that PacBlue provided about the gear boxes is something I might never have known otherwise. I'm still a bit dumb founded that there doesn't seem to be anything other than anecdotal evidence/information available for these engines. Having said that, my original question has been answered as I no longer doubt the existence of the 6-71 TI rated at 410-hp. My concern all along was that it was a mistake made in the Powerboat Guide (should have been the 310-hp rating) that was simply carried over into the broker's listing. Thanks everyone who responded. Hopefully I'll be able to report soon that we've joined the Post family!
  8. P46-Curaçao

    P46-Curaçao Senior Member

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    I recently understood, that 6-71 TI HP ratings depends on the chosen injector size…
    Correct me if I’m wrong!!
  9. Capt Ralph

    Capt Ralph Senior Member

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    Injectors are a great part of HP changes. Piston types, fuel pump, 2/4 valve heads, tall vs original height blocks, cam timing, air cooling, blower ratios, turbo performance, exhaust tuning AND more, represent other parts of creating HP on any 2-stroke DDC block.
    Any of these components can be adjusted and weighed against engine life. Some aftermarket shops and installations did well, some not so well. I think 485hp was the big wall on da 671.
    410s I think had a pretty good life IMO.
    I always thought the ole Post were ideally powered vs life of the motor and NOT high strung. Have an old Post next to me with pancake 671s. Last I saw her run (long ago), it was impressive. Another with 8v71Ns is my fave. Been surrounded with Post these last few weeks. I understand another 2 slips away has 8v92s. She has to fly.
    But all that know me here, I'm a 71 guy.

    Have your soon be yours surveyed well. Get tight with a proven good local shop and bring them coffee often. No matter what anybody says, a good old Detroit tech (NOT some bilge punk) can be a very good friend (to many punks out there).

    71s rule,
    rc
  10. RT46

    RT46 Senior Member

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    J&T is an excellent source.
    I have been in contact with them and the had the original build sheet and sea trial results for my boat.
    All you will need is the serial numbers.

    Just keep in mind that the engines could have been modified over the years.
    To be 100% sure you will need to have a tech pull the valve cover to see what is stamped on the injectors and get the part number for the turbo.
  11. Capt J

    Capt J Senior Member

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    Mainly WHO marinized them. Each company J+T, Covington, S+S, etc. Used different injectors, turbo's, injector timing and other bolt on parts mainly that changed the HP rating. J+T was used mostly by Post as far as I know, if not exclusively and usually put the largest turbo's and injectors. Injector size is the majority of it, but some added larger turbo's.
  12. RT46

    RT46 Senior Member

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    Internally the heads (4 valve vs 2 valve) and pistons (Compression) are different
  13. dennismc

    dennismc Senior Member

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  14. Capt Ralph

    Capt Ralph Senior Member

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  15. Capt Fred

    Capt Fred Senior Member

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    Boatdiesel.com maybe another good resource for Detroit Iron and gears.
  16. PacBlue

    PacBlue Senior Member

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    With regards to parts / service on Capitol Marine gears, a lot will depend on which model gearbox it is. On some models, clutch packs and bearings are nearing "unobtanium " status, while others have some more availability. Last time I checked, full rebuild was running near $13K apiece, and that was with some scavenged / used parts. Regardless, I would check / replace ALL gearbox hoses when buying the any used boat with Capitol gears.
  17. Blue Goose

    Blue Goose New Member

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    I did visit the Boatdiesel.com site and had the same experience as I've reported above. Lots of anecdotal information shared amongst boat owners; but as on this site....zero technical resources referenced other than the suggestion of contacting the shop that might have done the mods to the engines on Post's behalf. I'm amazed that there doesn't seem to be one manual, exploded view, service bulletin...anything of an official nature to document these engines. Frankly, it has made me very Leary. If you look up any old CAT, MAN, VOLVO, PERKINS you are buried under piles of information. Search these engines until your fingers go numb from typing and your results will be a collection of boaters asking questions, and a collection of answers from other boaters....and nothing else. I appreciate everyone's input and I think it says a lot that all of you responded to a new members inquiry. So from a newbie...Thank You!
  18. Blue Goose

    Blue Goose New Member

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    P.S. If anyone is interested, the boat we are interested in can be viewed on the Temptation Yacht Sales website (Harrison Twp., MI). I would be grateful to anyone who takes a look and could give me a heads up to any potential issues they see. It's the only Post they have listed, so you can't miss it.
  19. RT46

    RT46 Senior Member

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    I just checked out the brokerage add for the boat.

    if I were in the market, I would want to go see this boat.
    Its hard to judge from pictures, but this boat looks real nice.

    cosmetically it seems to be well cared for from the pictures, that is usually a sign that the structure and mechanics are well cared for and maintained. wax and varnish are usually the first think to go....

    The mains could use some paint, but at least they didn't do a quick spray job to try to make things look nice in the ER.
    Last edited: Feb 8, 2015
  20. Capt J

    Capt J Senior Member

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    UMMMMM well, don't you think a phone call or email to the source, a Detroit Diesel dealer or THE Detroit Diesel dealer that marinized yours would give you all the information you want? Does it even matter what is in them? At 410HP they last, are reliable, and aren't too high in the HP ratings and the maintanence is the same. I'd also much rather have them then the same ERA/HP Man, volvo, or Perkins, even more then a 425hp 3208 (which didn't last....at 1800-2000 hours they needed rebuilds). 410HP 6-71's should go at least 5,000 hours between majors if not abused and more than likely closer to 10,000. I could walk into either local DD diesel dealer here with your serial number and they can tell me any part that is in YOUR motor.

    See, the thing is, each company that marinized them did many different modifications to get to their HP rating, depending on what they were seeking or even what type of boat they were being put in. With the serial number, just about any DD dealer can look up exactly what's in your set. All of the 410HP J+T's had the same exact parts in them from engine to engine. Some owners even had dealers modify them to achieve different things. I ran a 58' Hatteras YF where the owner had DD of Daytona install 90 LPH injectors instead of 110LPH to save fuel and for them to run cleaner on the low end, without changing anything else.

    CAT's also had some varients just like the D.D.'s. The origional 3412's were marinized by either Key Power or Gold Coast marine (I can't remember which), but they have lots of different parts on/in them that aren't Caterpillar parts, some might have even been made by the dealer. Then CAT stepped up to the plate, saw enough demand, and marinized the 3412's in house. There were other engines like that as well in the CAT lineup.