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385XP with low compression.

Post in 'The Gear' started by Sean McGillicuddy, Jan 3, 2013.

  1. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    If the compression is low would this indicate a scorched piston?
    How hard is it to replace the piston?
    Is the piston all that needs to be replaced?
    Thanks for all the great info found on this site.
    Sean

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  2. ScotO

    ScotO Guest

    Low compression could be caused by a number of things. First off, make certain that your spark plug is seated the whole way (make sure the compression washer is squished down). Next, make sure your decompression button isn't sticking. If you find that the rings are the problem, chances are you may need a cylinder as well. If you are doing a tear-down, look the cylinder and piston over real good for abrasion and deep scratches. Usually when the rings wear out, the piston gets sloppy in the cylinder causing the skirts of the piston to rub against the cylinder walls. If that's the case, you're gonna need a piston, cylinder and rings. While your at it, check the bearings on the crankshaft and also the crankcase seals......you'll have the saw torn down, may as well put new seals in as its a cheap insurance policy.......
  3. lukem

    lukem Minister of Fire

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    How low is "low"?
  4. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    Was running and while idling it shut down! Could not be restarted. Took it to a saw shop and the gent held the pull rope, and we watched the saw fall to the end of the pull rope. Was told low compression / scorched piston.
    What or how to test compression the right way?
  5. lukem

    lukem Minister of Fire

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    It the rope can't hold the weight of the saw, a bad p/c could very well be the cause. Check to make sure the plug and decomp are working as Scotty mentioned earlier (dealer may have already done that if he was worth a darn).

    If you want to test it you'll need a compression tester...should be north of 150 PSI.

    If you don't have one pull the muffler and take a peek at the piston and cylinder.
  6. ScotO

    ScotO Guest

    Your shop should have a compression gauge. To me, anything below 90-100 lbs is worthy of a look. Good compression is up around 130-150lbs.
  7. MasterMech

    MasterMech Guest

    If the dealer was really interested in telling you what's wrong with your saw, a compression test (with a real comp gauge) and a leak-down test would have pin pointed it. At the very least, pull the muffler and visually check the piston.

    De-comp valve is a very common cause of low compression so check that before moving on to the more expensive things.
  8. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    To all!!
    The saw in question that I thought someone was holding for me went to the big scrap yard in the sky!!
    Only if!!!
    Oh well thanks all!
    Will not make that same mistake again!!::-)
    Sean
  9. HittinSteel

    HittinSteel Minister of Fire

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    What? Some idiot trashed a 385?
  10. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    I killed the saw long before I found this site. After reading and watching vids,, I said I can rebuild it. Went back to gent and we looked in his pile..No luck .
    Day late dollar short.
    Will not do that again!
    Sean
  11. MasterMech

    MasterMech Guest

    Never EVER leave a saw you don't desperately want to be rid of in a dealership or small engine repair shop. ;) I highly doubt that saw went to the scrapyard. It's most likely cutting wood for some lucky Craigslist/Ebay user this very minute. Or at the very least,parts of it are. You always can hold on to it yourself until you decide. Then donate it to his cause or sell it as a "parts" saw. 385XP in decent cosmetic shape would have brought a couple hundred, even with a bad top end.
  12. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    ;hm
    PapaDave likes this.
  13. MasterMech

    MasterMech Guest

  14. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    Come on more salt!!! ;sick
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  15. lukem

    lukem Minister of Fire

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    That 385 never existed. You only think you remember owning one...and it dying...and you dropping it off at the dealer...and it disappearing. None of that ever happened. A figment of your imagination.
    PapaDave likes this.
  16. MasterMech

    MasterMech Guest

    A co-worker of mine once said "School costs money." So true.

    Don't worry, I've made a few costly blunders before. (and I'm sure I'm not done! ;lol) Not trying to rub it in or embarrass you. Just showin' ya the light. ;)
    PapaDave likes this.
  17. HittinSteel

    HittinSteel Minister of Fire

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    Did he at least offer you something else out of his pile?

    btw, I never intended to call you an idiot, in case it came across that way...... I was talking about the person who "threw it away".
  18. Sean McGillicuddy

    Sean McGillicuddy Burning Hunk

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    I am the idiot for leaving it!
    But I do have a 350 with a scorched piston @ home.

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