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Crank Seal Replacement on Stihl motor.

Post in 'The Gear' started by Drifthopper, Jun 18, 2013.

  1. Drifthopper

    Drifthopper Member

    Joined:
    Apr 12, 2007
    Messages:
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    Crank seal replacement, behind the flywheel on a Stihl 2 stroke : How difficult is it…?

    This is my Leaf blower – StihlSH 86 C . 27 cc

    Was using it last week, started up as normal to blow the grass clippings off the driveway, set it down to move some lawn furniture,,, picked it back up and I had no high RPM’s… it idled but wouldn’t rev.
    I figured the plug finally went or fouled out. Bought the unit new in 9/09.
    So ..went to the local Stihl dealer and bought an $8.00 spark plug,,
    And it still ran the same,,, rough idle, no rpm’s.

    Took it apart,, and oil all over the outside of the case.

    It appears to be coming from behind the fly wheel, I’m guessing the seal.

    Any input is appreciated.

    http://s463.photobucket.com/user/Dr...002014A9950EC_zps13f5fad9.jpg.html?sort=3&o=1

    http://s463.photobucket.com/user/Dr...00200E5AA0AE4_zpsb5068f70.jpg.html?sort=3&o=0

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  2. MasterMech

    MasterMech Guest

    I haven't had my SH86 apart but it should be similar to others. Once the flywheel is off you can pry the old seal out carefully, avoid nicking the case bore or the crankshaft surfaces. They make a special puller for it but it's very expensive.

    The bigger question is why did the seal fail so early in the life of the machine? Make double sure that the bearings are good or the new seal will fail quickly as well. Also check the crankshaft surface for scoring.
    smokinj likes this.
  3. ScotO

    ScotO Guest

    I can't figure why it would idle at all if the crank seal was bad.....it should run at high throttle if that was the case.
    Not saying that it isn't the crank seal....but I'd look it over really good because if the crank seal was bad, that would cause a lean issue and the motor should run at high throttle and possibly stall out.....
  4. Drifthopper

    Drifthopper Member

    Joined:
    Apr 12, 2007
    Messages:
    90



    I’m only guessing that the crank seal is bad. I tried to Google search it,,, but only came up with motorcycle threads.

    It was like one minute is was running fine,,, set it down, go to pick it back up and its running like garbage.
    It would idle…. rough thou, and when I squeezed the trigger to fully open, it would still run, but wouldn’t gain any RPM, then I let off, and it stalled.
    Then thought it was the air cleaner, that was good, then took the plastic side shroud off and seen the oily crank case.

    But , even when I put the new plug in it, it started on the 2nd pull, ran rough, but no RPM.

    I’m guessing the crank seal, once I took the plastic shroud off, the whole outer crank case is covered with oil residue, and there nothing on the flywheel. (photo bucket sucks with trying to copy an image)

    Ya… I’m po’ed too that this thing went down on me already… I use it, but not excessively. And ..its not like i don't have enough things to work on this summer.

    To check if the seal is bad, if I started it up, and sprayed starting fluid behind / around the back of the flywheel, would the engine rev..??

    And…once apart..... How do I check if the bearings are good?
  5. MasterMech

    MasterMech Guest

    If it will idle then spray carb cleaner (starting fluid is a no no for small engines, especially little two cycles) at the seal area and note any change. Pressure/vac test is best but not every homeowner is setup for that.

    To check the bearings, with the flywheel on it, try to move it laterally, you should not be able to move it any noticeable amount. Some movement parallel to the axis of the crankshaft is normal.
    smokinj and pen like this.
  6. Drifthopper

    Drifthopper Member

    Joined:
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    Bringing this one back to the top….

    …and.. ya… A search function will be a nice addition to this board.

    After having this thing sit on my Bench for the past 2 months…. I finally got around to asking more about the problem.

    Talking to my snowmobiling buddy, he suggests talking to Wally…. Another friend who fixes small engines on the side.

    Wally says it the fuel,,, “its not getting enough gas, the ethanol ate the diaphragm”

    So I buy a carb re-build kit….. no change.

    Talk to Wally again…. “oh….. you gotta adjust the carb,,, break those plugs” …..i was like huh…???

    “hey…. Wally…. Can you look at it for me?”

    “Bring it to me”

    45 minutes later….. “All Set”

    I think he tried to adjust the carb,,, but after that had no effect on the low rpm’s…… he must have taken off the exhaust…. Cuz he commented that he cut out the California emissions …

    “Your spark arrestor screen was clogged”

    I was ready to take the clutch off and replace the crank seal….. I’m glad it was something “simple” .

    Its back in action now…. The cottonwood in the backyard is already dropping its leaves.
  7. HittinSteel

    HittinSteel Minister of Fire

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    To avoid this in the future, what ratio of mix were you using?
  8. pen

    pen There are some who call me...mod. Staff Member

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    glad you got it running better.

    As hittinsteel mentioned, try some higher octane fuel that's fresh and make sure you are using the right oil in the right ratio. That should not have plugged so soon.

    search function is near the top on the right just under the stove pics. It works great.
  9. Drifthopper

    Drifthopper Member

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    I typically run a mix of 3 oz of oil to a gallon of gas.
    Maybe ….. just maybe ,, in the past I’ve ran 4oz to a gal, but nothing more than that, but 3 oz is what I mix.
    I have a separate gas can, just for the leaf blower and weed wacker… and since Sunoco is close, I run their 91 , if not their 94 octane.

    Should I go to a 50:1 mix…???
  10. HittinSteel

    HittinSteel Minister of Fire

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    I'd run 50:1 with a modern 2 stroke synthetic oil (cheapest is poulan synthetic at walmart).
  11. lukem

    lukem Minister of Fire

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    There's no reason not to, but 3oz to1 gallon isn't far off (~43:1). I'd say your oil may be suspect and not your ratio.
  12. Drifthopper

    Drifthopper Member

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    As for oil, having snowmobiles, I would think I’ve been using “good” quality 2 stoke oil right along.
    I’ve used the Ski-Doo semi-synthetic oil for my mix, and recently,,,, maybe the past 1yr or so…. I’ve been mixing Klotz Sno-Mo TechniPlate full synthetic oil, its got a nice aroma to it, it reminds me of being at the races when I’m out weed wackin’ and out cutting wood.
  13. charly

    charly Guest

    Do yourself a favor and run some seafoam in your mix... 2 ounces to a gallon... I've ran it for over 15 years in all my fuel, cars everything... FS130 stihl trimmer is 10 years old, MS360 stihl saw 12 years old,, all have original carb parts, etc.. Trimmer has about 3-4 tank fulls run through each time I trim on the farm here... saw sees about 10 cords a year on average... Amsoil 2 stroke for mix,, Dominator racing oil.. Stuff always runs, always! Just trying to keep ya trouble free!
  14. Foragefarmer

    Foragefarmer Member

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    Don't use snowmobile oil that is your problem right there. Oil formulated for large water cooled 2 strokes are not appropriate for small air cooled engines. You should use an oil formulated for small 2 stroke engines.
  15. TreePointer

    TreePointer Minister of Fire

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    Agreed. Chainsaw makers do not recommend any water cooled 2-cycle oils or multipurpose air/water cooled 2-cycle engine oils (anything that has a TC-W rating).

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