Twin V6 to single diesel conversion

Discussion in 'Propulsion' started by burt2, Nov 19, 2005.

  1. gonzo
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    gonzo Senior Member

    That's and OMC Cobra drive. The name Cobra covers a lot of models so it's confusing. With 4.3 engines the gear ratio is about 1.65:1 . With lower revving diesels you would need a lower ratio; probably around 1.20:1. It would depend on the RPM rating.
  2. cyclops
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    cyclops Senior Member

    Burt. I am sorry I did not see your request for Michigan Wheel Corporations web site. Old brain.-------It is should be very accurate for a cruiser boat. That is their bread and butter line of prop sizes and shapes. Do the prop selector forms with the present engines and drives. Then the other guy who posted his results. Then start entering what engines and drives you would like to get cruise speed and gpm. Then if nothing still looks good give them a call at the ----outboard & sterndrive division. ------Better yet E Mail at----- spent$ 60 on Tech. Assist., But the props were so close to perfection. :)
  3. burt2
    Joined: Nov 2005
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    burt2 Junior Member

    Thanks guys, well still so many paths to take and I have been thinking about buying a new stern leg (bravo 2). I don't mind playing with old gear as im not rich but the engine and stern drive is the most important part of the boat.

    Also I have been offered a 6.2 Star Power V8 turbo diesel for a good price and it comes with a stern drive to suit, although the prop looks wrong as it was off a 40' semi-displacement launch. 6.2 Star Power is just a Chevy right? Looks like one.

    I’m doing this boat with my father and we both decided that we want a single engine, we will put it on a poll mooring down a tidal river we don’t need to manoeuvre round tight mariners.

    I would still like to find out more about the cobra drives so I know exactly what I got.

    Attached Files:

  4. drs3317
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    drs3317 New Member

    The 6.2 is a chevy diesel motor. It was known for cracking heads. They usually crack from the water jacket to the exhaust valves. That said, I had a 1985 Suburban with the 6.2 and it actually was a very effecient motor. Mine cracked the heads at about 120,000 miles. I replaced the heads and run the truck to almost 500,000 miles before it was totaled by a drug dealer being chased by the police. The factory never used turbochargers on the 6.2 but after market turbos are available.
  5. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    My grandfather's been running a Cobra drive almost identical to yours, with a 4.3L V6, on his boat for 18 years. I am aware of exactly one major incident, when it threw a bearing and seized a shaft last year (we suspect this was the mechanic's fault, not OMC's). That was kind of scary, but not dangerous and was quick to fix.
    Check the gearcase oil (dipstick's on the top of the upper unit, it's the large flathead screw in the middle of the top panel of the upper unit housing, if I recall correctly). If it's low, or contaminated, your drives have probably been poorly maintained. If the oil's full and clean, and everything else checks out OK, I'd think the drives would be good for some time yet. But if you're repowering anyway, it's probably best to follow Cyclops' advice and go for new rebuilt drives. I'm kind of leery of going to a single from twins, but if you're confident that you can safely rebuild the transom, the Starpower unit could work.
  6. burt2
    Joined: Nov 2005
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    burt2 Junior Member

    I can’t find anything bad about the marine 6.2 and it would fit nicely (might have to cut into and reinforce the two center stringers) also comes with the above stern leg, does any body know this leg apparently it’s a really strong commercial leg.

    Changing from twin to single won’t be a big deal I have done plenty of laminating like this; also I will over engineers it to be safe (might laminate a new stringer in).

  7. MAD JAX
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    MAD JAX Junior Member

    Twin-screws to Single-Diesel conversion...

    Interesting Thread...I'm in the throes of doing this of late, just need to install some Stringers.

    Please reply as to the out-come of this project, Thanx!
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