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Stihl 191T cracked connecting rod

Post in 'The Gear' started by Boog, Oct 31, 2012.

  1. Boog

    Boog Minister of Fire

    Joined:
    Oct 31, 2012
    Messages:
    592
    Loc:
    NE Ohio
    Hi all. This is my first posting to this group so please bear with me if I don't post things quite right. I recently started having problems with my MS191T saw. It would start up and run just fine. After cutting awhile and shutting it off, I could not restart it....seemed like it was flooding out (smelled gas). Tried starting it as warm or cold, it wouldn't matter. However hours later, or the next day, it would start fine, then cause the same restart problem. Suspected it was probably due for a carb rebuild, but I figured to take it to my local Stihl guy and let him check it out. He rebuilt the carb (I knew I should have just done that myself and saved $) and it ran beautiful again. Two tanks of gas later the connecting rod broke punching it through the wall of the upper crank case. I have since tore it appart myself, secured a used crank housing and nice used crack assembly on ebay. The piston and cylinder looked very good, so I just cleaned up the piston and put new rings & a new wrist pin on it. I'm getting ready to fire it back up but wanted to first see if anyone has any idea as the the root cause of the problem so it just does not repeat itself. I always used Stihl oil at the proper mix, and as far as I know, my carb settings were ok. The saw had about 9 years of moderate use trimming/limbing smaller stuff. Anyone have any thoughts?

    Stihl MS191T
    Stihl MS250 C-BE
    Stihl MS440 Magnum - 20/24/28" bars
    70's 20 lb Sotz "Monster Maul" splitter, other lesser wimpy devices for small stuff.
    80's Charmaster wood/oil forced air furnace
    25 acres mixed Ohio hardwoods: Red/White/Pin Oak, Smooth/Shag Hickory, Beech, Cherry, Maple, Ironwood, dying/dead Ash.
    Sell my big logs as timber and burn the rest. Plant native Oaks, Black Walnuts, & Evergreens where I've tread.

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  2. MasterMech

    MasterMech Guest

    Busted rods come from excessive vibration (or over-revving) or defective materials. If the saw was otherwise in good shape, maybe you just had a bad part. I'd fire it up, run it, then run it hard, if it holds, call it good. Check the max RPM against Stihl's spec and tune the saw so it four-strokes at WOT no-load.

    Maybe put 'er up on CL and go drool on a MS192T. ;)
  3. Boog

    Boog Minister of Fire

    Joined:
    Oct 31, 2012
    Messages:
    592
    Loc:
    NE Ohio
    Thanks for the comeback MasterMech. I fired it up this morning and it seemed to run beautifully, but I haven't run it hard or cut with it yet. "Four-strokes at WOT" - your going to have to explain that further for me, my specialities are in Bio/SafetyTech, not MasterMech ;-). My only experience rebuilding engines to date was tearing into an old Kawasaki 500 back in the early 70's. Working on that small saw was a lot easier than I figured it would be though. Is there really that much difference in performance between the 191T and 192T saws? There is one for sale here on the site right now. I did notice that there are a lot more 192T than 191T parts available on ebay though. It would probably be the better one to have for the long haul. Thanks again!

    Ahhh - Figured it out MasterMech (knew what a four stroke was but not in the relationship to two stroke engines) Now the obvious follow up question ..... why would I want it tuned to that extreme of what is defined as an "abnormal operation"? I know I don't want it on the leaner side of things, and if anything want to be on the slightly richer side of the fence for lubrication issues.

    four-stroking - A type of abnormal operation of a two-stroke internal combustion engine where the cylinder only fires every second cycle (like a four-stroke engine does). This occurs when the exhaust scavenging and inlet charging leaves a mixture in the cylinder which does not ignite, but needs a second scavenge/charge to produce an adequate mix. (Wiktionary)

    WOT - thats got to be wide open throttle!
  4. MasterMech

    MasterMech Guest

    The MS191T didn't really have a great following. Actually, it kinda flopped. The MS192T came back as a much lighter saw with better AV. For $300. That put the nails in the 191's coffin.

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