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  1. #1
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    25' Checkmate Convincor I/O to twin O/B's

    Always wanted to do this and finally flipped the switch after stumbling on this donor.

    Timing couldnt have been worse with it requiring a road trip to Philli a wk before we were to move but I try not to let common sense interfere w/my boat buying decisions.

    I've restored two twin O/B 24' Sonics and owned them for 14 yrs collectively. Way longer than any other boat Ive owned.
    I loved them.
    Not the Sonics so much as that type boating. They were inner liner boats and I didnt like that.
    But, something about driving them and then being able to spend the weekend on it.
    I remember shopping for the first one and talking to a dealer in NY w/one for sale and he told me on the phone, "they're a drivers boat, and a hand full to drive fast".
    That was all I needed to hear.

    Anyhow, to the Checkmate.
    I sold them in '89/90 and we had two I/O 25' Convincors and I spent that entire time looking at dealer pricing trying to make the math work on a O/B model but I wasnt even close to being able to afford a new one at the time.

    On top of that, the O/B versions had splash wells and no sun lounge. Two big strikes for me.
    If you pull the motor out of an I/O version you end up w/a garage under the sun lounge! And we use our boats as boats.
    So that storage will hold our two fold up bicycles for exploring, the Walmart dinghy to get to shore from anchor, chairs, grill etc for the beach.

    So yrs ago I came up w/the idea of finding an I/O boat w/a popped motor (making it cheap), pull all the cast iron crap out and selling it and the drive train to help fund the project.
    And to find a clean one.
    So Im only doing the conversion and not a complete restoration like both Sonics.

    The donor:

    '1986 Convincor w/a stroker 454 that dropped a valve and a Bravo drive on a near new aluminum trailer, which I really wanted.
    Previous owner redid the interior but unfortunately stored it outside w/a leaking cover so a bunch of that wood needs redone.

    The boat is a very rare white w/silver stripes, which Ive never seen before, that I love.

    W/our move, I lost my shop until building a new one which will probably be spring thanks to our Ohio winters.

    All I have now are "before" pixs.

    On power, I explored all options.
    I established a $10K budget for power.

    Im still brain storming on brackets too. At current prices of new, Im inclined to either draw up plans and take them to a local fab shop or build one out of glass.
    The bracket on the 2nd Sonic was glass.

    Today I committed to a pair of '2009 300 hp E-Tecs with '2013 factory replacement, full dressed powerheads.
    Having them inspected/tested Monday.

    The good is, these are the 3.4 liter stroker motors.
    The bad is, they have the gargantuan magnum gear cases. Likely, I will replace them w/the smaller standard 3.0 cases and keep the magnums as backup.

    Ill also paint them silver to match the stripe on the boat then do graphics for them in black.
    They should pop.

    Wont be able to do much until new shop is built, or spring, whichever comes first.
    That will kill me.

    Should be a really nice, rare piece when done though.

    PS, mistakenly put this on the tech page orig.
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    Last edited by Instigator; 01-12-2018 at 08:33 PM.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  2. Likes Dave Strong liked this post
  3. #2
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    I stumbled on this the other day and really like the comparison/differences between the two.

    The Sonics had an 8' beam where the Convincor is only 7 1/2' but the the Sonics lost cockpit/interior space to the liner so they're actually very close.
    You can see how much deeper the Sonics were.
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    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  4. #3
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    Those motors are gonna make you throw every carb part u have in the dumpster.

    Keep a close eye on cyl 4 they crack the block behind the sleeve and start spraying water in that cyl. Might be why the Powerheads were replaced. Out of the 25 3.4s I’ve owned I’ve fixed Atleast 5 and have 5 more that need to be fixed. Granted I only buy them broken.
    Quartershot T-3R 15" E-Tec 1.62 sportmaster


  5. #4
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    Quote Originally Posted by baja200merk View Post
    Those motors are gonna make you throw every carb part u have in the dumpster.

    Keep a close eye on cyl 4 they crack the block behind the sleeve and start spraying water in that cyl. Might be why the Powerheads were replaced. Out of the 25 3.4s I’ve owned I’ve fixed Atleast 5 and have 5 more that need to be fixed. Granted I only buy them broken.
    Thx for the tip Bro.

    They were all running when replaced. Had them on a custom, dual station. 39' center console w/the "I-con" I think was called.
    Where the motors are fly by wire.
    Had unending problems w/that system and owned by a person of wealth and power ��
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  6. #5
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    Love the boat Gary, look forward to seeing it all done.

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

  7. #6
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    The later Ones are much more refined you will like them. Better ignition, better map and improved oiling but there’s an oil trough behind the sleeve. It lets oil out of a hole in the sleeve puts oil between the exhaust port and top transfer port. Well when the block cracks that oil hole pumps sea water out of it instead of oil. I’ve never met a dealer that’s herd of this problem but that’s cause they just call Evinrude and get a new Powerhead. I end up with the broken stuff and it usually rusts out the crank which is 3.4 specific $1700 dealer cost.

    I love my 3.4, 1.62 and a 32 pulls like a freight train.

    https://youtu.be/cu_9KvKxr2E
    Quartershot T-3R 15" E-Tec 1.62 sportmaster


  8. #7
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    Mirage Jaguar RiverRacer
    Polaris PRO785
    Bennington 255LCC

    Scream & Fly Flying Machine of the Month:
    September 2005

    http://www.screamandfly.com/showthre...ild&highlight=

  9. #8
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    I really like that in '13, they got all new, complete, dressed p. heads.

    MiamiDave sent me your video.
    Way cool!
    W/a 32"? I'd call that, TORQUE!

    That will be good for my pig too ��
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  10. Likes baja200merk liked this post
  11. #9
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    Your going to want a bracket with a good amount of floatation at rest

  12. #10
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    Quote Originally Posted by Capt.Insane-o View Post
    Your going to want a bracket with a good amount of floatation at rest
    Yep
    Both Sonics had that. First one came w/Gil brackets and were replace w/an integral platform w/a flotation and raised freeboard 4" as I recall.

    i should be able to drop some weight from motors but looks like I'll be adding 150 lbs compared to what I'm used to.
    Beam is 6" narrower too so I may have to play w/weight distribution.

    PS, your comment on the dinghy thread about a vintage motor has me going ��
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  13. #11
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    Quote Originally Posted by Instigator View Post
    Yep
    Both Sonics had that. First one came w/Gil brackets and were replace w/an integral platform w/a flotation and raised freeboard 4" as I recall.

    i should be able to drop some weight from motors but looks like I'll be adding 150 lbs compared to what I'm used to.
    Beam is 6" narrower too so I may have to play w/weight distribution.

    PS, your comment on the dinghy thread about a vintage motor has me going ��
    the style with a platform would make extra room for inflating water toys or the dingy you mentioned earlier.
    Mirage Jaguar RiverRacer
    Polaris PRO785
    Bennington 255LCC

    Scream & Fly Flying Machine of the Month:
    September 2005

    http://www.screamandfly.com/showthre...ild&highlight=

  14. #12
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    The big gear cases going to drag things down that much?

  15. #13
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    Quote Originally Posted by MODVP22 View Post
    the style with a platform would make extra room for inflating water toys or the dingy you mentioned earlier.
    Yep

    Once I replaced the orig Gill tube style brackets on the first Sonic, I was hooked. And think most larger O/B boats would be better w/one of these.

    FMP, I've heard everything from 3 - 6 mph's. and I will have two of them. Being bigger = heavier also. If I can save 10 lbs per, thats 20 lbs and Id be happy w/that.
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    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  16. #14
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    5 mph is noticeable but are you better in the heavy chop running hard with the big cases? 20 lbs , never notice it.

  17. #15
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    Quote Originally Posted by FMP View Post
    5 mph is noticeable but are you better in the heavy chop running hard with the big cases? 20 lbs , never notice it.
    Never had a problem w/the Sonics.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

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