Never trust the blue marks
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  1. #1
    PWCToday Regular
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    Never trust the blue marks

    As title states. Never trust the blue marks when timing the balance shaft to crank.

    Just finished building a 951 DI. Engine installed aligned, etc, etc. Cranks right up but shakes like a paint mixer. I mean it shakes.

    I remember thinking something was odd when I aligned the blue marks for timing but wrote it off as being a result of the air pump.

    With air pump at TDC the mag piston is no where near TDC. As far as I can tell when mag piston is at TDC so should the air cylinder.. Can anyone confirm?

    Also, I think I have come up with a way to fix the timing without tearing down the entire engine. Again some input would be appreciated.

    Can I put the engine upside down on the bench, and just split the case halves, correct timing and rebolt the case halves together? Am I asking for trouble doing this? If at all possible I'd like to avoid having to buy a new headgasket, possibly new base gasket, reseat the rings, etc, etc, etc.

    Did I mention that you shouldn't trust the blue marks?

  2. #2
    Top Dog Benflynn's Avatar
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    Re: Never trust the blue marks

    I would start with why they are wrong, and I see no reason u can’t pull the bottom

  3. #3
    PWCToday Regular
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    Re: Never trust the blue marks

    Quote Originally Posted by Benflynn View Post
    I would start with why they are wrong, and I see no reason u canít pull the bottom

    Motor was just rebuilt and reinstalled. Fresh rebuilt, crank, balance, pistons, sleeves, etc. etc.

    Presumably crank builder pressed gear on wrong. I rebuilt the balance shaft myself, marked everything and did not even remove the gear.

    Scouring the forms yields a few other cases of incorrect marking of gears -- even found a case of it happening to Bill.

  4. #4
    Top Dog SURFnTURF's Avatar
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    Re: Never trust the blue marks

    Turn upside down, Remove lower case, align crank by using case half surfaces and weights for crank and balancer being opposites. Apply Gasket sealer, torque up. Have done it a few times, some my fault, some the machinist.

  5. #5
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: Never trust the blue marks

    Yeah I did one wrong once....ski shook so bad spilled my Mt Dew.

  6. #6
    PWCToday Regular
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    Re: Never trust the blue marks

    Quote Originally Posted by SURFnTURF View Post
    Turn upside down, Remove lower case, align crank by using case half surfaces and weights for crank and balancer being opposites. Apply Gasket sealer, torque up. Have done it a few times, some my fault, some the machinist.
    Thanks, good to know. engine is pulled and on bench. Might try and power through it today.... I do need to eat at some point though.

    Quote Originally Posted by Grumpy Old Guy View Post
    Yeah I did one wrong once....ski shook so bad spilled my Mt Dew.
    :lmao

  7. #7
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    Re: Never trust the blue marks

    I have the bottom end open and the timing is totally wrong. Blue marks line up as I remember. But something definitely seems off with the balance shaft. I rebuilt the balance shaft myself, but everything I took off was marked, and on reinstall the marks were lined up.

    The balance shaft weights are closer to 90deg off than 180. I thought this had something to do with driving the air compressor piston -- but I question what is correct? The air pump was in rough shape when I rebuilt it. Perhaps it cause the counter weight to rotate? It seems highly unlikely. The air pump rod wasn't bent or anything like that.

    At any rate that's not the only problem. The mag side balance weight is 180 of where it should be, so I may have more than one problem.

    Some pictures to describe what I am seeing:

    IMG_4728.JPG

    IMG_4759.JPG

    IMG_4760.JPG

    IMG_4761.JPG

    IMG_4762.JPG

  8. #8
    PWCToday.com Is My Home Away From Home kcr357's Avatar
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    Re: Never trust the blue marks

    definitely off. The counterweights on the crank should be 180 off of the balalnce chaft weights
    How many gerbils could a gerbil jammer jam if a gerbil jammer could jam gerbils?


    "You build cheater motor's & still get smoked !!!!"
    "Its not your fault. You just don't understand what you're talking about. "

  9. #9
    PWCToday.com Is My Home Away From Home kcr357's Avatar
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    Re: Never trust the blue marks

    That shaft isn't usable as is.
    How many gerbils could a gerbil jammer jam if a gerbil jammer could jam gerbils?


    "You build cheater motor's & still get smoked !!!!"
    "Its not your fault. You just don't understand what you're talking about. "

  10. #10
    PWCToday.com Is My Home Away From Home kcr357's Avatar
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    Re: Never trust the blue marks

    A blind person pressed that balance shaft together.
    How many gerbils could a gerbil jammer jam if a gerbil jammer could jam gerbils?


    "You build cheater motor's & still get smoked !!!!"
    "Its not your fault. You just don't understand what you're talking about. "

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