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Easy compression test for chainsaw?

Discussion in 'Mechanic and Repair' started by terrapro, Aug 15, 2010.

  1. terrapro

    terrapro LawnSite Bronze Member
    Posts: 1,234

    I heard somewhere that if you hold the saw by the cord and it drops easily on its own the compression is bad. Would this always be true?

    I have an stihl 029 I recently accuired for cheap that I can't get to run properly. With the plug out and a finger over the hole you can feel good pressure but when I do the cord test it drops pretty easily.

    I have had the carb apart half a dozen times to no avail, anyone have any ideas? Should I buy a new carb or dig into the motor deeper?
  2. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    To be a little more conclusive, connect with someone who has a compression gauge. What you describe doesn't sound good.

    Pull the muffler and take a look at the condition of the cylinder and piston.
  3. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    I think those tests are probably about as conclusive as checking tire pressure
    by pushing your thumb against the sidewall, somebody with years of experience
    might be able to tell you something doing things that way but I would get yourself
    an inexpensive compression gauge.
  4. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Posts: 1,415


    Another simple way is to dump a tad of 15W-40 oil in the cylinder and give it a pull, if it's harder to pull your engine is dead.

    Honestly take it to a shop, they charge $15-$20 for a compression test and you know where you stand.
  5. terrapro

    terrapro LawnSite Bronze Member
    Posts: 1,234

    Took the muffler off on th e029 todat and the cylinder was smooth as a babies butt but the piston seemed grooved?

    Had it running for alittle after I put the muffler back on but couldn't get it to idle right but it had a good rev to it.
  6. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    If you have some metal transfer evidence on the piston you likely have the same thing in the cylinder. That most often happens on the exhaust side but is not limited to that. Get a compression test on it before you spend any serious amount of money on it.

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