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Stihl FS85 clutch problem - lock up

Discussion in 'Mechanic and Repair' started by Roger, Apr 11, 2006.

  1. Roger

    Roger LawnSite Fanatic
    Posts: 5,923

    I have had a Stihl FS85 string trimmer for more than four seasons. I have used it to start the season, trimming out only about 20 lawns. Today, while I was using the trimmer and moving from one bed to another, the trimmer was idling. I felt a bit of a "clunk," an unusual blip in the usual smooth running machine. It was nothing big, but enough for me to notice.

    I resumed trimming, but quickly noticed it didn't feel/sound quite right. When I went to idle, I realized the trimmer head was still turning. And, when I exercised the throttle, I then understood the head was in sync with the engine.

    When I finished, I saw the trimmer head stop in sync with the engine. When trying to turn the head, it wouldn't turn. Apparently, the centrifugal clutch has locked up.

    I continued to use on the next job, and learned it responded just a bit differently. The head is still locked up with the engine, but after turning it off, I was able to wiggle the head so that the clutch was freed. But, I hear a scraping sound in the area of the clutch. It is not a hard sound, but enough to notice. The head isn't totally free, like it should be.

    What has happened to the clutch? Anybody have this happen to their FS85 (or FC85 edger)? I can still use the machine. It is harder to start because the head is being turned too during startup. The lockup seems to happen quickly upon pulling the starter rope.

    What is involved in taking it apart? And, how? What parts may be damaged and needing replacing? Help!
  2. hosejockey2002

    hosejockey2002 LawnSite Bronze Member
    Posts: 1,195

    Roger, check your owner's manual but I think the clutch on the Stihl commercial series tools has a lifetime warranty. If so, maybe you can get it fixed free.:payup:
  3. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    My guess is that you have a broken spring(s) in the clutch assembly. In the shop I worked in for a while we had numerous commercial guys who ran their trimmers without a shroud and thus excessively long line. This condition puts more stress on the clutch drum assembly causing it to overheat. I'm not saying that you're running long line, but it definitely contributes to clutch problems. It could be that the spring(s) just fatigued and failed.

    Just my two cents worth.

  4. lucforce

    lucforce LawnSite Member
    Posts: 223

    Yes, broken clutch spring.
  5. dchd1130

    dchd1130 LawnSite Member
    Posts: 6

    life time warranty on the clutch drive shaft and possibly ignition depending on when you bought it they only give you a 5 year on the ignition now but thats a life time for a trimmer for most commersial users
  6. Roger

    Roger LawnSite Fanatic
    Posts: 5,923

    Thanks for the replies. I used it all day today without problems. At the moment, I don't have time to tear it apart and install a new spring. Knowing past dealer history, if I took it to them for warranty repair, I would not see it for weeks.

    In an ironic twist, the previous day the ignition module gave up. I had used the trimmer for three morning jobs, and went to the fourth. It would not start -- very strange behavior.

    I know the module is bad because it switched it out. I also have an FC85 edger. I use the edger far less, so I pulled the module off the FC85, installed it on the FS85, and it works fine. I inquired about a new one, and none were in stock. However, I was told it has five year warranty -- I bought in Aug 2001, so I'm just under the wire by a couple of months.

    I have not talked to the dealer about the clutch yet. When the module arrives from the order, I will talk with them. As long as I'm not doing further damage to the trimmer, I can use it in the locked state, but fix it on a rainy day. I do not have doubles of equipment -- work solo, small operator.

    This is a situation where I wish I had a parts/assembly drawing. Stihl is so stingy with this information. They gave me one with my new Stihl chain saw, but none for trimmer, edger, hedge clipper or blower -- only owner's manual.
  7. davhul

    davhul LawnSite Member
    from Gray,Ga
    Posts: 51

    do you have a fax I could fax you the breakdown with part #'s
  8. Roger

    Roger LawnSite Fanatic
    Posts: 5,923

    OK, I bought three springs today. I was able to see the parts/assembly drawing, and see three springs on the inside of the clutch.

    Does anybody have any suggestions or insights into the repair? I see the T-27 screws holding the clutch housing onto the engine. The throttle cable will have to come off. Should the two parts separate when the bolts are removed, giving me access to the springs? The drawing looks that way.
  9. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    You have to remove the clutch housing from the crankshaft. Are you sure that you dont want to take to the dealer?
  10. Roger

    Roger LawnSite Fanatic
    Posts: 5,923

    No, I don't want to take it to the dealer, if I can avoid doing so. History has shown me it would be gone for weeks. I'm a solo, use it 6-8 times per day, and am not large enough to have doubles/backups of my equipment. The dealer who supplies parts gave me encouragement to make the spring replacement -- they know me pretty well, the parts I have bought from them, the kind of repairs I have made, etc. I think if they thought the repair was very difficult, they would have raised a flag. If I get an indication the repair is nearly impossible for a non-trained person, then perhaps I am better off to use it as is. The season is just beginning, 45 of 1,200 mowing jobs (expected) completed. If the season was October, then I would not bother, but work until season end.

    Maybe the dealer is counting on me having trouble, showing up with a box of parts, need a trimmer, so will come to buy a new one to resolve the problem ... maybe that is their strategy.

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