Yanmar 2V78 Saildrive

Discussion in 'Diesel Engines' started by sgancarz, Sep 28, 2015.

  1. sgancarz
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    sgancarz Junior Member

    I am looking to do an engine conversion for my sailboat. The boat had an OMC saildrive in it at one time. I picked up one a while back however the engine is seized up. I really don't like the idea of the 2-stroke inboard engine, so I am looking to install a diesel engine in place of the original powerhead.

    Yanmar made a vertical shaft, water cooled v-twin a few years back. I just recently picked up a brand new unit to accomplish this swap. These engines were originally installed in John Deere lawn tractors. The unit produces 18HP @ 3600RPM. The boat I intend to install this into is a 26ft monohull with a displacement of approx. 6,000 lbs.

    Does anyone see a problem with using this engine for my intended purpose?
     
  2. gonzo
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    gonzo Senior Member

    The gear ratio is likely to be wrong. Do you have the RPM ratings for each engine?
     
  3. sgancarz
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    sgancarz Junior Member

    Looks like the OMC was limited to 3700rpm and Yanmar is 3600rpm. So both look really close in that respect.
     
  4. sgancarz
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    sgancarz Junior Member

    Here are some pics of the engine.

    [​IMG]

    [​IMG]

    [​IMG]
     
  5. FAST FRED
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    FAST FRED Senior Member

    Should work fine , how much heavier is it?
     
  6. sgancarz
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    sgancarz Junior Member

    It's about double the weight. Original powerhead was about 60lbs. This one will be about 112lbs.
     
  7. FAST FRED
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    The only other problem might be that the unit is not strong enough.

    The torque rise when a cylinder fires is harder , sharper with a diesel than a gas engine.

    Only time will tell if its robust enough for the extra hammering underway,

    Either it will fail in a very short time , or you will get a good service life .
     
  8. sgancarz
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    sgancarz Junior Member

    I plan to use a Lovejoy L-type jaw coupling to couple the engine to the drive leg, as there is a significant difference in the arrangement of the output shaft on the engine and the input shaft on the drive leg. One added advantage of this it that is should help to absorb some of the impact of the increased power stroke of the diesel. The only thing I am unsure of is the life expectancy of the rubber spider used as the cushioning component of the coupling.
     
  9. sgancarz
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    sgancarz Junior Member

    Not sure if anyone is familiar with the old OMC saildrive or not. However I have a question regarding the mounting of the new engine.

    The OMC saildrive uses what they call an iso-ring to seal the space between the lower unit and the mounting plate for the powerhead. Additionally it serves to isolate the vibration of the engine from the hull mounting plate. Basically this is the one and only motor mount.

    I am wondering if the iso-ring will be sufficient to isolate the vibrations of the new diesel engine as well as be strong enough?

    Additionally due to the shaft lengths and the shaft coupling, I am going to have to elevate the engine plate approximately 5 1/2" above the mounting plate on the lower unit. I intend to do this with 1" round stock using 7/16" bolts to secure them to each of the mounting plates. These will rigidly tie the engine to the lower unit and rely on the iso-ring to serve as the isolator.

    Does anyone see any problems with this approach?
     
  10. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    Lovejoy Coupling

    I had a single cylinder diesel in generator service, and had to get a flex coupling to even out the power impulses from that setup.

    The best I could find is the Lovejoy S-Flex design, much better torsional stiffness than the jaw types, meaning a low torsional spring constant. They are not too expensive, and will virtually eliminate the impulsive hammering on the gearbox.

    The Lovejoy L type couplings handle some mis-alignment, but are not torsionally soft, so they are not the best choice here.
     
  11. sgancarz
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    sgancarz Junior Member

    After looking at the specifications for the S-Flex coupling, I think that this would definitely be a better choice. One added benefit is that it allows a much greater misalignment, which would allow me to utilize separate mounts for the engine.
     
  12. sgancarz
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    sgancarz Junior Member

    Well here is a drawing of the my design. I will be using 6" aluminum channel to create the uprights. As I said, I have decided to use the Lovejoy S-type coupling instead of the L-type.

    Everything from the blue intermediate housing down is the original OMC drive leg and mount. Everything above that will be part of the new install. The overall height is actually about the same as the original OMC unit. It does however have a little larger footprint. Hopefully I won't have to move too much to make room for it.

    [​IMG]
     
  13. sgancarz
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    sgancarz Junior Member

    Been a while since I posted on this, so thought I would provide an update.

    I have completed the rebuild on the drive leg with all new bearings and seals. I have also acquired the parts and completed the machine work to the original input shaft on the saildrive for the coupling of the engine to the saildrive leg.

    [​IMG]

    [​IMG]

    I also filled in the orignal water intake in the drive leg, being I have decided on the external raw water pump. However, the original raw water pump I purchased had some severe scoring and I didn't trust a rebuild, so I have purchased a brand new one.

    Yesterday I did a test fit for the new engine mounting platform. It is made from 5" steel channel attached by two strips of 3/16" bar stock. I will also be adding flange shielding to either side of the mount. These will be made from 1/8" steel plate, to add additional rigidity to the mount.

    [​IMG]

    I also started cutting the hole back into the bottom of the original saildrive motor mount. I discovered that the previous owner used a 1/2" of fiberglass and 3" of wood to fill in the original hole. Now I need to figure out how I am going to get all that wood out of there without damaging the original housing. Have a feeling it is going to take a bit of time and patience.

    [​IMG]
     
  14. stone beach
    Joined: Dec 2015
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    stone beach Junior Member

    I recommend you rethink your engine support arrgt.
    Your 2 channels are almost sure to oscillate on the flanges, if you form a box by plating across the open ends it would improve it...maybe that is what you meant by " adding flange shielding " ?? not sure..but you would do much better to fabricate a "bell housing".
    Not criticising your basic idea, just suggesting you re engineer the drive motor support.
    2nd comment. Guess you have checked the compatability of the shaft coupling and the flexible motor mounts ?? incorporating a support "damper" within the bell housing might be a better solution ? not sure how to do that..is that what the iso ring was ?? something like a thick reinforced rubber disc, something like the drive plate within a flexible shaft coupling ??
     

  15. sgancarz
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    sgancarz Junior Member

    Yes, the flange shields are to help stabilize the channel by creating a complete box. I figure the 1/8" plate bolted at all four corners should provide enough rigidity.

    The iso ring was what was originally the isolator(motor mount) for the entire engine and lower drive leg with the OMC Sailrive, as well as the watertight gasket through the bottom of the boat. For my setup, it will pretty much just provide the watertight integrity for the hull penetration and will support the drive leg.

    The engine will be mounted on four individual isolators atop the two main channels of the mounting pedestal. The engine will then be coupled to the drive leg using a Lovejoy S-Flex coupling. This will act as a torsional shock dampener and provide allowances for minor shaft misalignment.
     
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