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  1. #1

    how often do keys on crank break js550

    this is the second used key i put on my 2mm bored over 550 and broke while riding. is it just that im using used keys. is it time for a new one? also the timing mark should be even with two case halfs right?


  2. #2
    Both the 550 and 650 have adjustable stators to change the timing. It would be a really good idea to look into a manual on the timing if you want to toy around with it. As for the flywheel key shearing, a person should always use a new key. If the old one is even just slightly marked from before, for example: a little offset to it, or a line showing where it was pressed against the crank...it could be enough to throw off the timing. Plus it's integrity will be sacraficed enough that the key won't last long.

    If after installing a new key and it happens again then it could just be that if the ski is being jumped, and the throttle is held wide open, the water load against an unloaded high revving engine will overwhelm the key and shear it. Anytime a ski leaves the water the throttle should be off until back in the water. If this isn't done, there could be a double negative effect on the engine. Not only could the flywheel key shear, but revving the engine dry so to speak (out of the water with no coolant being pumped) could result in a blow-up or a good start to one.

    I think trying a new key should be the first step and go from there...in fact, pick up a couple of them to save the trip into the dealer should it happen again. Best of luck on that one.

  3. #3

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    Quote Originally Posted by tchamb2 View Post
    this is the second used key i put on my 2mm bored over 550 and broke while riding. is it just that im using used keys. is it time for a new one? also the timing mark should be even with two case halfs right?
    try lapping the flywheel to the crankshaft,then before putting flywheel on just warm up the taper part with a propane torch,not much (250-300 deg.)then install while still hot ,also toque to proper ft lb's
    and good luck running 2mm over bore on that motor it will need LOTS of cooling water to keep running

    later cd

  4. #4
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    Explain why to heat the taper and not the flywheel. I would have thought to heat the flywheel to get the flywheel farther up the taper before it tightens itself down and grips the taper.

    Always learning

    thanks

  5. #5

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    sorry may bad grammar,yes the taper on the FLYWHEEL
    after it cool it bites better-sorry about that chief

    later cd

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