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Removing Westerbeke Back-End. BTD-8.0 from 21A Diesel Engine

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    Removing Westerbeke Back-End. BTD-8.0 from 21A Diesel Engine

    I recently separated a Westerbeke BTD-8.0 generator from the 3 cylinder 21A diesel engine that drives it while both units were still in my boat so I thought I'd create a thread in case anybody else needs to do this. Some background: I just bought a 1987 3870 and I knew that the genset was not working when I bought it. I was told maybe bad starter, maybe a little seized up, but I didn't really know what the problem was. So I started investigating. It became apparent that the engine looked fine but the generator bolted onto it (commonly called the back-end) looked like it was likely the problem. This turned out to be exactly the case, for as soon as I got the back end off, the crankshaft turned freely, and before it was seized solid.
    The main message I'd like to convey in this thread is that this is definitely a job you can do on your own if you are reasonably handy and have a good set of tools. It can be done on your boat. It is not fun, but it can definitely be done.
    Westerbeke has some manuals online that were somewhat helpful. One is just a parts list really, but that does help. The other references a WMD generator disassembly and while that is a little helpful there is some stuff in there that does not exist on the BTD Genset. Here's my guide:
    1. Remove the starter motor. It's pretty easy, just a couple of bolts and electrical stuff. It will probably be a little stuck on, give it a whack but do be gentle, replacement starters are actually pretty expensive for this model so if yours showed any signs of life treat it well. This will let you peer in at your flywheel.
    2. Lift and support the back end of the engine so that the generator is not resting on its isolators. Basically this means stick some 2x4 or something under the engine to raise it up a bit and take the pressure off the mounting feet. These 'Isolators' are the rubber mounting pads that bolt to the support struts. If your genset is in as bad of shape as mine was, removing the mounting feet bolts may be the hardest part of the whole job. I had to cut through these bolts with a grinder and a reciprocating saw because they were so badly corroded. If your genset has been sitting in water, this is where it will be hardest hit. So don't be surprised if you can't remove these bolts normally. Cut them off any way you can. Cut the support strut if you have to, but you have to release the generator to move back horizontally somehow.
    3. You don't need to remove the little endbell cover at the very back of the generator. There is a bearing at the end of the armature that fits into the back of the generator bell-housing but you don't have to pull the bearing or use any special tools to separate these units. You do need to remove the slotted back cover so you can disconnect your main electrical connection. This is held on by a couple bolts and a couple flat head screws. I had to cut off a couple of these too, just too badly corroded.
    4. Remove the control panel from the top of the generator. I was able to leave mine wired in and just removed the four nuts that held it to the generator body. I also had to remove the fuel filter body so that I could get decent access to one of the mounting bolts. You will have to remove the main electrical connection (just three leads) so make sure you take a picture of the wiring before you do that.
    5. Unbolt the generator housing from the engine. The bolts that hold the back-end on are pretty obvious. Remove them all. Again, this could be pretty simple or some of your bolts could be badly corroded. I was able to get all mine off with copious amounts of PB Blaster and by putting a hammer to the end of a wrench in stubborn cases. Make sure you get them all though.
    6. Once the bolts are all out and the mounting feet are free, the back end can be removed, but it will likely take some coercing. I had to hammer a slotted screwdriver into the gap between the mounting plate to get mine moving. There are also some little studs that extend from the mounting plate into the back-end, you will likely have to pry around those points to get it to go. Try to be gentle but realize it will likely take a little abuse to get it off. It is unlikely your armature is of any value but try your best to support the back end as it falls to the floor of your bilge.
    7. Now you're staring at the the armature and fan assembly still bolted to your flywheel. Remove the bolts that secure the fan. you should be able to rotate the flywheel with a little effort at this point. If your flywheel is frozen at this point that is bad news, and means you engine has some issues. Hopefully you can rotate your flywheel in a clockwise direction and remove the fan bolts one by one. There are quite a few of them.
    8. Now the fan is loose but the darn thing won't come off, the armature is wider than the inside diameter of the fan housing. What's going on? How to get to the next layer of goodies? This was a surprise to me, but the armature is held onto the flywheel by a set of friction plates. Mine popped off while I was prying at the bearing on the other end, wondering if I needed some sort of special puller. You don't. Just apply a little pressure and hopefully your armature will pop off too.
    9. Once the friction plates have popped off, you have access to the bolts that hold them to the armature. Undo the bolts and you can separate the fan, armature, and plates.
    At this point you're pretty much done. Your back end is separated. Lug those parts (likely scrap) off your boat and go look for an aftermaket or rebuilt generator to bolt back on once you clean things up. I haven't gotten that far yet so I can't comment on your chances of success. I took my back-end to a local electrical rebuilder (I live in Victoria, Canada) but they told me it was scrap. Maybe you live in a more competitive market and can get it rewound? Not an option for me. I'll post some photos to help illustrate things.

    #2

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      #3

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        #4

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          #5
          Man...Thank you so much. This is EXACTLY the kind of info that makes this site so great.
          Drew Haas
          1998 4788 "Painkiller"

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            #6
            Bry, when you get done, put this information in the completed projects forum. That way it’s less likely to get buried in time and will be more readily accessible to others.
            Its too bad that rewinding is becoming a lost art. When I was growing up my grandfather was head millwright at a saw mill and my dad was general manager of another. There were always several motors at Everett Industrial Electric being rewound. They are still in business but I have no idea if they still do it. Nowadays it’s so often more economical to replace rather than rebuilding.
            P/C Pete
            Edmonds Yacht Club (Commodore 1993)
            1988 3818 "GLAUBEN”
            Hino EH700 175 Onan MDKD Genset
            1980 Encounter Sunbridge "Misty Blue" (Sold)
            MMSI 367770440
            1972 Chevrolet Nova Frame off Resto-mod in the garage
            Boating on the Salish Sea since 1948

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              #7
              OK, now that you have it off, could you do me a favor, and in return I will do you one as well

              If you are going to replace the generator end?????

              I have been selling Marathon generator ends for two decades, but have never been able to determine if a Marathon generator end can replace the westerbeke unit. I have always suspected that it would but I have no hands on time with a westerbeke generator to tell for sure.

              If you are willing to take the measurements, and work with me to figure out if one of my Marathon Magnaplus generator ends will work, I am willing to sell you one at my exact cost in return.

              If this works out and if we find that a Marathon generator end will fit, then in the future I will be able to offer a replacement solution for Westerbeke generators at a price point that is a little over half of what you’l pay for a Westerbeke generator end. Plus the Marathon unit is far better quality than the Westerbeke. (Northern lights for example use Marathon generator ends on most of their generators).

              Please let me know

              Here is my main web site

              www.generatorparts4less.com

              KEVIN SANDERS
              4788 LISAS WAY
              SEWARD, ALASKA

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                #8
                I'll definitely get in touch with you Kevin. I still need to clean things up and make sure the diesel engine does work before I can commit to replacing the back-end but that is what I want to do. Look for something from me in about a week.

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                  #9
                  Originally posted by BryGuy View Post
                  I'll definitely get in touch with you Kevin. I still need to clean things up and make sure the diesel engine does work before I can commit to replacing the back-end but that is what I want to do. Look for something from me in about a week.
                  Sounds great! this could be a win win situation. The big thing that hopefully will come out of it is that Westerbeke owners would have an option...An option they do not have now.

                  KEVIN SANDERS
                  4788 LISAS WAY
                  SEWARD, ALASKA

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