Marinizing Audi 2.5 TDi (5 cyl) - Questions

Discussion in 'DIY Marinizing' started by Engmark, Jun 11, 2014.

  1. Engmark
    Joined: Jun 2014
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    Location: Bodø, Norway

    Engmark Junior Member

    From the top! I have a Bayliner 2455 which is around 2500 kg with engine. I bought it with a Chevrolet 6.2 Diesel which had been marinized. Long story short; last fall the boat sunk. A sunked boat have little resell value once it been rebuildt, so I don't want to throw money in a whole - so I need to keep it cheap. I have rebuildt several cars, so familiar with engines but need advice on the marine part.

    To the issue. I have previously work with Audis, and I love the 2.5 TDi 5 cyl 140 hp engines. They last "forever" and are more powerful than the numbers suggest. They are easy and cheap to come by, the are easy to maintain and I have a garage full of spares for those engines.

    I want to marinize that engine into my boat with OMC Cobra stern drive. Why? Because it will be half the weigth of the 6.2 which gives less weigth at the rear, which gives me more clearance to the engine vents, it get the lowest two trough-hulls over the water line, it comes faster up when accelerating (can't remember the word) it gives better accessibility in the engine bay, it fits my toolbox and I have spares for it. Also when chiptuned it will be more powerful than the 6.2 D. So a lot of pros. Also, I find the 6.2 D really unappealing.

    I've been googleing and I found nothing about marinizing this engine, but I've managed pick up some tips and tricks along the way. My plan is to go the same "route" as they did with the 6.2 D. Which is heat exchanger fed by impeller, water manifolds with raised exhaust where the saltwater is pumped back and replacing the frost plugs. I will not be changing starter, alternator, oil pan etc, since this being a budget boat. I think it will hold up without those parts.

    What I concider to be the biggest challenge is the coupler. I have never done anything with a coupler before, so I don't even have full understanding of how it works. But I am a quick learner!

    So I would like some input on both the marinizing in general, but most about how I can hook the engine up to my OMC Cobra drive the easyest way. I have a gearbox for this engine lying around, so I can pick up a grinder and get a bellhouse from it.

    Also, is there something else I am missing? Making stuff spark safe I can't imagine beeing an issue since it's a diesel and the engine room is very well vented. I will paint the engine to keep it from rusting up too fast, so oil pan will be standard.

    I want it to be somewhat reliable (not sinking, blowing up or stopping every five minutes), but it will be a BUDGET build with help from friends with different skills. I am thinking putting less than 2500 $ into the marinization, part funded by selling of the kit I've got.

    So; start talking people! Especially want some feedback from CDK if he reads this, I think he always give good down to earth edvice, rather than point out that spending less than 10.000 $ will just make everything s**t :)
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    You already have all the marinization parts for the 6.2, so, if budget is your biggest concern, the cheapest solution is to find another truck motor to bolt in.
    You will probably not be happy with the type of power the audi produces, and the longevity in marine application may not mirror its automotive reputation.
    If you want to pursue this discussion with some real marine diesel professionals, post your question on boatdiesel.com
    In any case, good luck with your project, sinking is never much fun, is it!
     
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    I've read your post, but I'm pressed for time right now.
    Did you already buy the engine?
     
  4. Engmark
    Joined: Jun 2014
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    Location: Bodø, Norway

    Engmark Junior Member

    kapnd:
    Sadly, I guess it is something that I have to concider, to find another 6.2 D. I say sadly, because it's like this with most american engines, they just come out as lazy really. I have compared the power/torque curves from the 6.2 and the 2.5, and the 2.5 is better on everything above 1500 rpm. Longlivity - yes, you never know really, but the odds are good. A lot of 500+ hp tuning builds on Audis are based on this engine. Thank you for the link, I will check it out - and hope it's not one of those (many) forums that shoot things down just because you don't want to spend 10.000 $ in a heartbeat. (which is really annoying, it's always like that on forums - I once turbo converted a car and everybody said it would cost 4000$, and there was no way to get around it. I made some of the custom parts myself and spendt a total of 1000$)

    CDK:
    Sure, no problem. I have a 12 month perspective on getting this up and running so no hurry. Have not bought the engine yet, no. A complete car with engine will be around 6-700$, so that I get the wiring etc.
     
  5. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Your Bayliner is a planing hull, and if you use it mostly in planing mode, you need extra beef under the hood. While the Audi motor can produce 500hp, it will not last very long in that state, especially in a boat.
    If you are a cruiser who is happy at 8 knots or less, the smaller engine will do fine.
    A good comparison of a marine engine to an automotive engine is if you drove roads that were only uphill all the time, no coasting. The resistance of the water is constant, the marine engine must work hard ALL the time.
    This makes the difference in displacement of the two engines in question a clear choice for the 6.2 IMO.
    That said, I am not a huge fan of the GM 6.2 as a marine motor, I would put my money on a 6 cyl diesel Volvo duoprop for an application like yours. (just my opinion!)
    or switch to a gasser if your boat is not a daily driver.
     
  6. CDK
    Joined: Aug 2007
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    CDK retired engineer

    "What I concider to be the biggest challenge is the coupler. I have never done anything with a coupler before, so I don't even have full understanding of how it works. But I am a quick learner! "

    The coupler is nothing more than a replacement for the clutch plate / pressure group that resides in the flywheel cavity. Because OMC drives were designed for GM engines, the mounting holes do not fit the VAG clutch pattern, so you'll have to drill and thread new ones.
    No big deal as long as you make sure the splined hole is exactly centered. Copying the hole pattern of the pressure group on the coupler plate is another option if your bench drill can cope with tough steel. I prefer the flywheel modification; drilling in cast iron is a lot easier.
     
  7. Engmark
    Joined: Jun 2014
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    Engmark Junior Member

    kapnD:
    The 2.5 TDi are common in 500+ hp projects, however I would only chiptune the engine from 140 to about 175 hp. Otherwise it would be stock. In that state it produces similar curves (torque / hp) to the 6.2 D (better in some areas) while only being half the weigth. So in theory it would have the same power and it would act as if there were two persons less in the boat.

    CDK:
    Yes, I was not making myself clear there. I ment the bellhouse. It's a matter of engeneering it I guess. The way I see it, I can

    A) Use my current bellhouse and fit an adapter plate between that an the engine - worrie : correct distance to engine

    B) Cut down my current bellhouse, weld an adapter plate to it, and do the same with the bellhouse from the original gearbox of the audi engine

    C) Construct a new bellhouse


    If I can use option A that would be the easiest. But how likely is it that this would add up with the correct length? What do I need to concider here?
     
  8. CDK
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    CDK retired engineer

    If you are willing to sacrifice the old bell housing, an adapter plate is the easiest way, assuming the hole patterns do not interfere. The advantage is that you don't have to make the two protrusions that rest on the transom housing.

    I suppose the GM flywheel is a bit thicker than the VAG one, so if you use steel plate with the proper thickness, the coupler will reside at approximately the same distance from the transom.
     
  9. Engmark
    Joined: Jun 2014
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    Engmark Junior Member

    CDK, I am misthinking here?

    If;
    B= Bellhouse / C= Coupler / F= Flywheel / A= Adapter / E= Engine

    then the distance could be something like this;

    Chevy:
    BBBBBBBBBBBBBCCCCCCFFFFE

    Audi:
    BBBBBBBBBBBBBCCCCCCAAFFE

    What worries me in that calculation is that the coupler will not reach the flywheel, since the 6.2 D problaly has a thicker one. Like I said, am I misthinking? Because is you add a adapter plate, then the coupler will rest further from the engine, and if the flywheel is thinner, it will rest further away from the coupler. In total maybe adding an inch or so?

    How can that be solved?
     
  10. CDK
    Joined: Aug 2007
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    CDK retired engineer

    You are right, I was wrong... very embarrasing.
    Looking at drawings from GM and VAG, it seems to me the GM flywheel is in fact large and thin, the VAG is smaller and thick, so that makes it a bit easier.

    Anyhow, if adding an 8 or 10 mm adapter plate would place the coupler too far away, the coupler plate must not be mounted directly on the flywheel face but on a support disc, using longer bolts.

    Finding a water cooled exhaust manifold for the 5 cylinder engine seems more of a challenge to me. The main source for such items, Bowman marine, only makes 4 and 6 cylinder VW manifolds.
     
  11. Engmark
    Joined: Jun 2014
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    Engmark Junior Member

    I pulled the 6.2 apart today just to get a better understanding. The one thing that struck me was that the bellhouse don't seem to do anything except to be the rear engine mount? The coupler just sits loose inside, so what else can it do?

    As for the flywheels, measurred the flywheels, both about 10 mm thick where the coupler was installed. However the bellhouse is humongous on the Chevy compared to the Audi, so an adapter plate would have to be big, and I would think it would easyilly flex.

    I studied the Audi gearbox, it seems that I can cut 10-15 cm of the bellhouse and the openin would fit the coupler still (before the cone gets too small). If my assumptions that the bellhouse only works as an engine mount, I would just weld new rear engine mounts to the Audi bellhouse. With a bit of fine meassuring, that should be an relativly easy fix?

    As for the watermanifolds, I studied my BARR manifolds today. They are just a boxed pipe; the far, upper and lower side has clearance to the pipe, while the engine has next to none. The "trumpets" between the manifold and the engine are uncooled, and you can fit it to the engine using studs + nuts, simplifying the manifold A LOT.

    Unless I am missing something very important here, this seems to be rather straight forward. Am I missing anything?

    PS! The bolt pattern on the Audi flywheel and the coupler does not interfear. Not a big clearance, maybe 7-8 mm, but that should do it.
     
  12. CDK
    Joined: Aug 2007
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    CDK retired engineer

    On most engines the bell housing serves no other purpose than to hide the flywheel and carry the weight of the engine block, on some VAG models it also carries the starter motor.

    Whatever you do, make sure there is a hole on top through which you can see the TDC marking on the flywheel, sooner or later you will need it.

    I know BARR makes products for US engines, but do they have anything that fits the 5 cylinder TDi? Or do you plan to make adapters?
     
  13. Engmark
    Joined: Jun 2014
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    Engmark Junior Member

    Thank you for clearing that up on regard on the bellhousing.

    When it comes to the manifold I am thinking of fabricating it myself. Basicly if I follow the BARR example it would be like this;

    [​IMG]

    Sorry for the bad drawing, I'm at my small laptop right now, but it should get the message across. Why does everybody think this is a big deal? I have done a bit of custom welding in the past, but for this I would bring in a friend which is an extremely good welder.

    What I am thinking is just making an collector / plenum from stainless steel, and box that in with stainless steel and fit it to the engine with some CRC cut flanges in stainless steel, and the same goes for the turbo.

    Is there any reason why this should not work?

    Right now I am feeling like a rodeo clown in a mine field. Everywhere I read it says do not even think about building your own marinizing kit, because it is so difficult. So I get the feeling that I have missed out on 80% of the information right now, because if this is what you need to do, it's not any harder than some of my previous engine builds for cars.
     
  14. CDK
    Joined: Aug 2007
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    CDK retired engineer

    With the right equipment, skills or a friend who has both, you can make anything.
    Assuming the mounting bolts are above and below the exhaust ports, putting the pipes at a 60 degrees angle makes a better manifold.
     

  15. bertho
    Joined: Aug 2006
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    bertho bertho

    hi guys,
    you have also this UK company " asap marine " they do custom manicooler , just check they website , I try to have one for a kubota 3.3 liter, but the maker (thermex) supply already beta marine for the same engine, and don't want to sell one for me.. strange sometime the business there... anyway, the profile they use for doing exhaust look good for your project, perhaps just purchase the suitable length !
    rgds
    bertho
    www.fusionschooner.blogspot.com
     
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