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Signs of crank bearing failure

Discussion in 'Chainsaw' started by Lawn Masters, Sep 13, 2004.

  1. Lawn Masters

    Lawn Masters Banned

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    Just wondering, what signs would be indicators of crankshaft bearing failure?

    I mean how can I tell without taking the engine apart and feeling for play on the crank ends? Would the engine make any unusual sounds when idling? rough acceleration or a shudder when accelerating from idle to wot?

    I need to know, since I have a machine with ball bearings that's making a slight whirring noise at idle.
     
  2. Mange

    Mange Addicted to ArboristSite

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    What saw is this and how can you tell, if the saw idles?
    Did you turn it by hand, with plug out?
    If you can hear noise on idle, i bet you hear more without engin on.
    I am not sure on the teknikal lingo, but from what I understand it`s a metall sound that could come from needelpins missing.
    I would take muffler off and take a look, perhaps stop the jug and wiggle engin by hand, then you can feel it.
    Perhaps it`s better explaind with a native mekanic.
    Well I tryed , hope it helps.

    Mange
     
  3. Lawn Masters

    Lawn Masters Banned

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    Well, actually the tool in question is a Stihl FS 85 trimmer, only about 5 years old with heavy use of about 700 hours or more.

    I dont really see how turning it over without a plug could help any, but I'll try tomorrow. the unit isnt here at home so I have to do it tomorrow.

    when I rev it up though I do notice a violent vibration from it, like either a bearing or something in the shaft thats not balanced right.
     
  4. Lewis Brander

    Lewis Brander Addicted to ArboristSite

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    Checking bearings.

    Have you ever heard of a dial indicator? Mount indicator so that your can measure the end play of the crank, then set it up to measure radial play of the bearings. With the plug out try and load the bearings a bit by hand and slowly rotate the crank to feel for any roughness or gaulling. If there's any question, then tear it down to inspect the brgs. To get some guestimate on rod brgs, remove the muffler and slowly rock the crank back and forth. The piston should move back and forth with the crank. The more lag there is in the piston moving with the crank would indicate more needle brg wear and teardown would have to be done for more through inspection. Same with the crank brgs. Ball brg should have very little or no play and needles, say less than .001" to .002" radal play. Course we're talking about a weedeater that's probably near the end of its usefull life and the cheapest thing would be to replace it with one of them thar 4 cycle machines. OK, rambled on enough. JMO. Lewis....
     
  5. stihltech

    stihltech Addicted to ArboristSite

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    vibiration

    Remove the shaft from the engine by loosening the pinch bolt and 1 locating screw. Now start it up. I am willing to bet your vibration disappeared.;)
     
  6. sedanman

    sedanman Just cut the piano!!

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    The string head could be packed with grass = unbalanced.
     
  7. joelamb

    joelamb Banned

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    Hey Rocky,

    How bout another picture of your Limp-Wristed chainsaw collection. I just loved it!
     
  8. joelamb

    joelamb Banned

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    OK Rock,

    And I'll bring my saws with me, LMFAO!
     
  9. Lawn Masters

    Lawn Masters Banned

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    I should probably mention that the original shaft housing was replaced after it got broken about 3 months ago. it got caught between a golf cart canopy and a fence post. snapped the shaft housing. Makes me wonder if the shaft isnt damaged and perhaps why it vibrates now this is a new problem, so maybe.

    Lewis, I think you're right about the unit being near the end of its useful life.
    I'd replace the unit in a heartbeat with an echo. gotta love a quieter engine.
    my only problem is money.
     
  10. a_lopa

    a_lopa Overhead downunder

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    money a common problem:D
     
  11. sedanman

    sedanman Just cut the piano!!

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    OSA, I doubt money is your ONLY problem.
     

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