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  1. #1
    EZ Dock of Long Island Shibby1485's Avatar
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    My Alternate way of ALIGNMENT for GPRXPs

    I posted this in my personal build thread... figured I'd post it here as well...


    I took a different approach to alignment of the rotax powerplant within the GPR Hull. I'll try to explain my rationale, however right or wrong, as best I can... I don't mean to imply those before me have done it wrong, because it has proven to work!! I just think this way is better and more accurate. probably me being overkill and too anal as i tend to be... naturally, the driveline is quite forgiving inside the crank snout alone with the crowned splines on the pto side of the 4-tec shafts and conversion shafts.


    My alignment procedure was made possible by Jason (hydrojunkie) and his RXP pump adapter plate... well that and thru my easy access to a seadoo alignment tool... By bolting his conversion adapter onto the GPR transom plate, i was able to have a 4-tec bolt pattern to then install the seadoo alignment tool.







    This helped in two ways
    • i was able to verify proper alignment of my GPR transom plate by leaving the alignment tool rather far out the rear and taking MULTIPLE reference points to ensure the distances were equal (ie measure from sponson blade to rod and other sponson blade to rod. measure from drain plug hole to rod and other drain plug hole to rod. measure from corner of hull to rod and other corner of hull to rod. there's infinite places to use as reference points to ensure the transom plate is in there totally square and center.
    • secondly, i was able to put the alignment pin insde the crank snout and then slide the rod thru the tunnel and play with the motor mounts and shims until the rod slid in like BUTTER. the rod slides into the pin a good 1.5 inches, so if u can slide it all the way in and out without any binding ur PERFECT.
      for example, you can get the rod to slide into the pin perfectly just so it starts to go in and bam, your aligned up down left right... BUT, that doesn't mean you are aligned thru the whole axis. the tool may slide in the first 1/4" easy, and then slope up from there and start binding as it goes further into the crank. My method covers every possible angle i feel. you could spend HOURS trying to be absolutely mental about alignment, or you can get it damnnn close and call it quits.
    **NOTE... i've mentioned this before, and i feel this is compelling evidence. my findings have been that the thru-hulls on the tunnels are not good indicators of true alignment. I measured a few 2-stroke GPRs and found that the driveshafts were not always centered in the niplpe on the thru-hull. After verifying my transom plate was square and center and on proper plane with the hull, i slid the rod thru the tunnel and it was very evident that the rod was not centered in the thru-hull..



    Last edited by Shibby1485; 04-28-2008 at 08:22 PM.


  2. #2
    Moderator RX951's Avatar
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    Is the transom plate sitting on all the alignment tabs on the hull ?
    Make sure it is, as the transom plays an integral part of how the pump shoe and intake grate fitment are....this is important on the GPR.
    Nice job shib

  3. #3
    EZ Dock of Long Island Shibby1485's Avatar
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    Quote Originally Posted by RX951 View Post
    Is the transom plate sitting on all the alignment tabs on the hull ?
    it most certainly is.... however mark kind of gave me a scare because i had my transom plate jacked up and clamped to the hull such that it was pegged against all those tabs as tight as possible... then he told me that the tabs aren't always right and i thought i messed up and maybe mine would be wrong...

    luckily, it seems my transom plate is dead on the money

    sometimes i overthink things a little and make them more complicated than they should be, but my mind wasn't at ease with aligning it as others have... so that's why i spent a few hours playing with this today and was able to draw several conclusions about the alignment of the plate to the hull and the alignment of the engine to the pump

  4. #4
    Moderator RX951's Avatar
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    Good Job Shibmeister !! Keep up the awesome work. I can't wait to see this ski in person !

  5. #5
    cheatin' piston popper addicted's Avatar
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    I like that. Maybe you could rent it out to the other guys building these?

    one question tho, don;t you need to install the midshaft with the engine for some reason? I can;t see why, but I thought that's how they are supposed to go together.

  6. #6
    Hydrotoys's Avatar
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    Hey Steve,
    so I finally got an alignment tool to play with, and I have a question.

    The alignment plate that bolts to the seadoo pump adapter, can move up/down/left/right based upon the slop on the 4 attachment screws. I'm seeing at least 2-4mm in any direction I want. I can tighten that plate down in any position I want, and it wouldn't seem to mean anything to how the pump would sit in there.

    My question, is did you have some way to keep the alignment plate from moving around on the SD adapter?

  7. #7
    2000 GPRXP 4tec shooter98xpl's Avatar
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    Just use a gpr pump without the driveshaft in it for your alignment.
    SHOOTER

  8. #8
    Hydrotoys's Avatar
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    Uh, yeah, I'm the one who wrote up how. But I'm trying to use this way too. I like to try new stuff.

    I took some heat shrink, and cut it into 1/8" strips, and put it on each pump bolt. That provided a shoulder to take up the slop. This cut the hysteresis down to nearly unmeasurable. It works great after that.

    Cut the heat shrink off when done.

  9. #9
    cheatin' piston popper addicted's Avatar
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    why not grab some flat head screws. even without a countersink in the plate, they will center themselves in the hole.

  10. #10
    Hydrotoys's Avatar
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    Sure, if you have some that big.

    I'm talking about the pump bolts, which are either 10mm or 12mm, (can't remember from the couch) and providing a shoulder to eliminate the slop from attachment of the flat plate to the pump adapter... and there is a ton of slop.


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