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  1. #1
    Moderator OsideBill's Avatar
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    GP1200 65U case porting project

    Gentlemen I would like to start a discussion about case porting on the 65U motor. A month or so ago I talked to Pistonwash and he was giving me lots of really good information on these motors. I was a good student and took lots of notes. One point that he stressed was that case porting was a huge boost to these motors. I have been working on my GPR so the 65U has been sitting on the bench in pieces and now it is time to start the build. I have had my crank trued and welded. I have my jugs freshly bored to .5mm over and new pistons that I balanced to within .1 gram of each other. I also chamfered the skirts and around the wrist pin area.

    Now I have no porting experience whatsoever but I am a capable machinist and very skilled with all hand tools. I am however disturbed by the condition Yamaha delivers these cylinders with the mismatch between the sleeve and cylinder I will take this to the profesionals for clean-up. When it comes to the case porting this is more conventioal and something I can do with tools I have at home.

    I was fortunate enough to have a ported case in my possetion that I could study and photograph and I am now going to begin my first steps into this arena.

    I am going to share the pictures and ask for your opinions and advice I will sort through the info and make decisions on what I feel is best and do the work and report all findings here.
    Last edited by OsideBill; 11-24-2006 at 02:04 AM.


  2. #2
    Moderator OsideBill's Avatar
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    OEM vs Ported

    The cylinders I had were ported and clearanced for a stroker so I will not be doing all the same work
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  3. #3
    Moderator OsideBill's Avatar
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    It bears noting that the last two pictures are with the cylinder installed and the skirt of this cylinder has been trimmed to match the ported area near the transfer port. also you will see in the pictures it was necessary to fill the void in the cavity above the intake as the porting will break through in this area. The person who ported these cases has the philosophy that rough texture is better and helps create turbulence and promote atomization. I have seen Lowell ported cases and his philosophy seems to be the opposite judging by his work, they appeared smooth to the point of almost being polished. The jury is out on this debate give me some feedback and opinions.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4
    Hydrotoys's Avatar
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    Porting the case is one thing... Gutting the case is a whole different story. I know the 65U is very sensitive to case volume. I don't know why so much more than other ones.

  5. #5
    Moderator OsideBill's Avatar
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    The ported case came from the race boat it seemed to me appalling in workmanship and finish. I saw what Lowell did on a gpr case completely different after Pistonwash explained the benefits of case porting I wanted to investigate further, so far this is the only example I have seen it is extreme to say the least but some of the logic seems sound to me. clearancing the skirt to improve flow radiusing the corners to improve velocity the roughness I am not sure I buy into.

  6. #6
    One day at a time..... N8R's Avatar
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    good luck on your project Bill

  7. #7
    Old Ski Insanity w/rpm500's Avatar
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    Bill, the x-h2O link has a bit on the 701 760 motors, that are sister to the 1200, take a look there for pics and discusions.. has some pretty good info
    look for cyl.porting and case porting in search!
    http://www.x-h2o.com/showthread.php?t=3301
    Last edited by w/rpm500; 11-24-2006 at 02:49 PM.

  8. #8
    Moderator OsideBill's Avatar
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    Thanks Nate

    W/RPM500 Thanks for the info I love homework. I had not considered this but you are exactly right about them being identical less one cylinder.

  9. #9
    Old Ski Insanity w/rpm500's Avatar
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    I also have the sport port template for the 760.... pm me if you wish further info... being a 1200, this may have just a slightly different porting spec. than the 760..also, there may be a change from cyl to cyl, for heat issues... ????(dont know)
    Last edited by w/rpm500; 11-24-2006 at 12:21 PM.

  10. #10
    ....back from the dead.... J-ME's Avatar
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    I am going to be pullin' the motor out of Jumper to rebuild the top and and have the crank serviced.

    As soon as I am able, I will post pics of the porting done by Dan Lamey. (both cases and cylinders)

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