SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Jan 2003
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    167

    Post

    If I were to have a bad crank bearing that siezes up the crankshaft, can that failure manifest itself in a broken rod?

    I have a failed 951 engine that has a broken rod, damaged case, and several of the bearings are very rough on the crank. The pistons and wrist pins look bad.

    I guess I am trying to figure out how a broken bearning can cause a rod to fail.

  2. #2
    Joined
    Feb 2001
    From
    Glendora, Ca.
    Posts
    5,204

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    With that many bad bearings and wrist pins and all, I'd guess the motor had water damage and the crankshaft got rusty.

    Depending where the rod failed, wether it was at the lower bearing or it broke up at the top is going to tell if the rust caused the rod to fail or if the rod got hydro-locked and bent before it broke.

    Where did the rod break, top or bottom? Does it look like the lower rod bearing disintregrated first, then the rod let go ? Or did the rod snap off below the wrist pin?
    Bill O'Neal WCM
    <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

  3. #3
    Joined
    Jan 2003
    Posts
    167

    Post

    Bill,

    I am having a bad wording day. The piston wrist pin bearings are intact with no visible damage. The pins never separated from the piston. The rod was broken in two places, an inch or two above the crank and about 1.5" below the piston.

    If the bearing failed all by itself, wouldn't the engine simply get hot and eventually overheat? Eventually, I guess that could cause a rod to fail....

    DWT

  4. #4
    Joined
    Feb 2001
    From
    Glendora, Ca.
    Posts
    5,204

    Post

    You described a rod that has at one time or another been subjected to a hydro locked piston, and was bent from it.

    My guess is that the motor was water flooded and the results were a rusty crankshaft and the bent rod, which usually breaks within hours of getting bent.

    A crankshaft bearing going bad will produce some heat allright, but it would be localized in the cases and not cause the beeper to sound off or even the head to get hot. Once the bearing went, no telling exacly what happened to the rod, other than it may have beat itself to death.

    [ November 25, 2003, 12:48 PM: Message edited by: Bill O'Neal ]
    Bill O'Neal WCM
    <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

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