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Pulled an "MM", punched a hole in my 460 too!

Post in 'The Gear' started by Boog, Sep 3, 2013.

  1. Boog

    Boog Minister of Fire

    Joined:
    Oct 31, 2012
    Messages:
    592
    Loc:
    NE Ohio
    I can now join "MM" to the elite select group of folks who have managed to punch a hole in their 460 while trying to repair them. Months ago I posted about cosmetically rebuilding my 460. It was the "Old ammo deal 440" if you remember that story. Tore it all down except the cylinder (had plenty of compression and the piston looked good through the exhaust port), evaluated everything, cleaned it all up, replaced/painted some parts, and its been sitting in the basement since.................. never tried to start it till 2 weeks ago.

    It wouldn't start after trying all the tricks ................ had plenty of spark ................. would just flood out if you kept on pulling. Started to realize that it didn't seem to have the compression that it used to............... this was a 460, and I was pulling way too easy. After fooling with this saw for hours, I was convinced that there was nothing else wrong with it other than it seemed to have lost significant compression. I decided to tear it apart again and pull the cylinder this time, figured maybe a ring had cracked or something. When I pulled the carb off, gas sprayed out of the tank/hose under serious pressure all over the place. **** I was seriously pressurizing the gas tank somehow by pulling on it trying to start it, figured crankcase pressure through the impulse line to the carb/tank - ?***** To my surprise I found the following:

    piston.1.jpg


    What the _ _ _ _ ! I was stunned, no wonder I was loosing compression and it wouldn't fire ;lol;lol;lol;lol . Then I remembered that I had removed the sprocket and clutch off the saw to clean them, using my piston stop tool to help get the clutch off. I have used the tool to remove clutches 2 dozen times now and never had a problem. I had always figured they could damage the piston with too much force, versus using the old rope technique. I rememberd that I had a heck of a time getting that old 460's clutch to break free .................. now I can see the force it took to finally "break it" ..................

    Oh well, already replaced the piston and have it all rebuilt and running fine, rebuilt the carb while I was at it too. I'm modifying the muffler at this point. Chalk it up to experience.

    I suppose this warrants a reconsideration of the use of metal piston stop tools versus the rope technique. I stopped using rope after having some rope fibers shave off inside and jamb in the ports/rings. Rope seems to easily get wedged onto "sharp" port openings. After this, I think I will keep using my metal tool carefully on the first attempt............... but if a clutch won't give and break free after "MODEST" effort I'll switch to rope and have at it.

    Most important of all, a good simple visual inspection of the piston through the spark plug hole when you're finished would have revealed the problem. I had that plug on and off a dozen times and never took a good look at the top of the piston :p.
    Last edited: Sep 3, 2013
    ScotO, MasterMech and clemsonfor like this.

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  2. StihlHead

    StihlHead Guest

    I use a red rag strip as a piston stop. It distributes the force and applies it more evenly. I never broke a piston even when I was drunk one night and tried to remove the clutch the right wrong way.

    On the right hand side, the clutch has a left handed thread. On the left side, the flywheel has a right hand thread.

    .
  3. MasterMech

    MasterMech Guest

    I use compressed air in the cyl and an impact wrench to pull the clutch. Often you can just use the impact with the spark plug in place to pull the clutch. Those metal piston stops are actually meant more for timing purposes than anything else.
    bioman and ScotO like this.
  4. DexterDay

    DexterDay Guest

    Rope still works well. Just make sure that you look in the spark plug hole and your piston top and rings are above the ports. Then add string. Then when tightening, same thing, pull rope, reverse piston to opposite side coming up, once above port, then start inserting rope.

    Easy peasy. Lesson learned. I have the piston stop. But every time I went to use it? I couldn't find it :) thank goodness.
    ScotO likes this.
  5. ScotO

    ScotO Guest

    I blew a hole in the piston of an MS170 I am rebuilding for my youngest son to learn how to cut with....I have three of those little 170's, thought about taking one out of another donor, but a HUZTL kit on ebay is 25 bucks with shipping, so I'll drop the clams on that here soon...
    Saw needed new crankcase seals when I started.._g..now it needs a total overhaul...;em.
  6. JOHN BOY

    JOHN BOY Minister of Fire

    Joined:
    Sep 20, 2012
    Messages:
    532
    Loc:
    Western Mountains ,NC
    Holy smokes ..I mean piston ..;lol

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