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  1. #1

    Importance of crank seals?

    How important are crank seals on a GP1200? I just did a top end rebuild and noticed that the crank seal near the couple was a bit crooked.... I just ignored it but have decided after breaking the new sleeves in that I might have screwed up by not taking care of it...

    A lot of people say the case needs to be split but other say it doesn't. The manual isn't very clear. Can I twist the coupler off using the rope method and replace the seal without taking it all apart?

    thanks!


  2. #2
    gp1200270's Avatar
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    Real important.With the seal being crooked chances are your compression will be low.If I were you I would replace with all new crank seals.Yes you have to split the case.I had to replace mine on my gp 1200 a few years back.It does take some time but is worth it.The front has 1 seal and the rear had 2 seals.Be sure when replacing the seals the rear tabs face towards the coupler.This is very important.Just take your time.

  3. #3
    Yes, you absolutely need to split the case but you dont necessarily need to pull the cylinders off. You can flip the motor over and split the case with the cylinder still bolted on. You'll still have to pull the flywheel and the coupler first.

    Check the crank bearings too. If they're not smooth, time for a rebuild.

  4. #4
    eb87's Avatar
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    If it's bad enough it could cause issues starting with lack of power up to running lean..... and we all know 2 strokes like to blow up when they go lean.

  5. #5
    well thanks for the feeback guys. I might risk it as the outer one is still 75%+ installed and I have alreday spent a ton of time replacing a crack in the hull, a blown cylinder.... Now I am struggling through the fact that the previous owner never tuned the carbs after installing an aftermarket flame arrester and removed the factory airbox.

    I just opened them up since they are dribbling and discovered a 1.2mm needle. I don't know how to size the spring or the other parts... but my couple hours of reading so far suggest i should make some changes... I just want this stupid thing to work and don't care about getting an extra 2mph for tons of research, tons more labor, and tons more tuning... The oregon riding season is only 2.5 months long

  6. #6
    Quote Originally Posted by tshank123 View Post
    Yes, you absolutely need to split the case but you dont necessarily need to pull the cylinders off. You can flip the motor over and split the case with the cylinder still bolted on. You'll still have to pull the flywheel and the coupler first.

    Check the crank bearings too. If they're not smooth, time for a rebuild.
    i missed this the first time. If I can flip it over and just split the case i might be willing to do that. I need to get a puller to get the flywheel off. Does anyone know if autozone rents a puller that works with this flywheel? I can order one for $20 from SBT if not.

  7. #7
    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by chadbobb View Post
    well thanks for the feeback guys. I might risk it as the outer one is still 75%+ installed and I have alreday spent a ton of time replacing a crack in the hull, a blown cylinder.... Now I am struggling through the fact that the previous owner never tuned the carbs after installing an aftermarket flame arrester and removed the factory airbox.

    I just opened them up since they are dribbling and discovered a 1.2mm needle. I don't know how to size the spring or the other parts... but my couple hours of reading so far suggest i should make some changes... I just want this stupid thing to work and don't care about getting an extra 2mph for tons of research, tons more labor, and tons more tuning... The oregon riding season is only 2.5 months long
    It is ABSOLUTELY critical that you replace bad crank seals. You will blow another cylinder within a very short period of time if you don't. This is your warning. Don't ignore it. Autozone should have a puller that works.

    If you have a stock engine with flame arrestors, I have a great carb setup you should follow:
    Use the 115 gram spring with the 1.5 NS to get a pop off of around 50 to 55 psi.
    All 3 carbs should use 100 pilots jets and the highs should all be the stock 135.
    Run the low speed screws all at 1 1/4 out and the highs at 1 1/2 out.

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  9. #8
    TexasZ's Avatar
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    Quote Originally Posted by Cutlass View Post
    It is ABSOLUTELY critical that you replace bad crank seals. You will blow another cylinder within a very short period of time if you don't. This is your warning. Don't ignore it. Autozone should have a puller that works.

    If you have a stock engine with flame arrestors, I have a great carb setup you should follow:
    Use the 115 gram spring with the 1.5 NS to get a pop off of around 50 to 55 psi.
    All 3 carbs should use 100 pilots jets and the highs should all be the stock 135.
    Run the low speed screws all at 1 1/4 out and the highs at 1 1/2 out.
    That's some dang good advise, along with some really valuable carb info. I would do exactly that.

  10. #9
    Myself's Avatar
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    Also agreed with the above. I know it's a pain but you really need to do this before costing yourself a whole lot of grief and money. I use a standard generic steering wheel/balancer puller on most all flywheels. Rope trick on the rear cylinder to remove coupler. Threebond for cases and I always smear a bit around the seals too, some grease inside the seal lips, medium strength threadlocker on all bolts. BE VERY CAREFUL running the flywheel puller bolts in. Too far and you can catch the stator and ruin it.

  11. #10
    Yamaha artisan Cutlass's Avatar
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    And that flywheel could be a pain. I use the same balancer puller. I put a bunch of pressure on it puller, and then smack the big, center puller bolt with a hammer. That'll make the flywheel pop off so be ready to catch it.

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