Stihl FS85 trimmer repair

Discussion in 'Mechanic and Repair' started by Roger, Jan 31, 2006.

  1. Roger

    Roger LawnSite Fanatic
    Messages: 5,940

    Perhaps my experience with my Stihl FS85 string trimmer will help out somebody else. I struggled a bit to make a repair and maybe these observations will help somebody else.

    My FS85 is four seasons old and has had heavy use. Near the end of the season last Fall, I noticed the starter rope to be frayed in one area. I thought this not to be unusual as I have restrung many other starter ropes
    in other equipment.

    When I was getting repair supplies from my Stihl dealer a few weeks ago, I asked for a length of starter rope for my trimmer. They gave me a four foot length of their smallest rope and I left. Later, I pulled off the starter assembly to put in the new rope. I discovered the take-up spool was damaged. One flange had a piece out (maybe a 25 degree section). The sharp edges of the flange caused the damage to the rope. Also, a spring-loaded pall attached to a convex disk on the end of the crankshaft was damaged. Apparently, the loose pieces of the flange had been engaged with the pall and worn off some of the nylon material. The pall engages the
    lugs on the spool when the rope is pulled. The spring pulls it back after starting.

    I returned to the dealer and got a new spool and pall. When I returned to the shop, I learned the disk (with the pall) was not easily removed. A 13mm nut was on the end of the crank, but I couldn't see how to
    get it off. Later, I learned the disk and the nut are integral. I had been trying to hold the disk to unscrew the nut, but that was wrong. The nut was only unloosened by an impact tool. I suppose the trick of putting rope in the spark plug hole to hold the crankshaft from turning could have been used. There is no direct way of grabbing the engine shaft when unloosening the nut.

    The disk had to be removed so that the pall could be installed. It is a delicate device, with a tiny torsional spring with two short legs. I learned the hard way -- take it to a place where the spring can be easily found when it pops out! Finding it on the shop floor in the midst of other debris was a difficult chore.

    The next issue was getting the rope strung in the starter assembly. I had a couple of false starts in getting the new spring properly engaged in the lug at the central point of the assembly. And, of course, the spring was out, laying on the bench a time or two as well. But, I did get it engaged and the central screw in place, ready to have a rotary tension.

    Now for the rope. I have done many of these over the course of time (previous post last Fall for a blower), and had just done a restringing of my 15hp Kohler. However, I soon realized I had met my match on this one. I just couldn't get the cord through the hole in the new spool. I tried several things, fine thread, fine wire -- trying to pull it through. I softened the end under a torch to shape it, attempting to make it as small as possible. I struggled for several hours, thinking that I must have gone loony-tunes in the last few days! Why was this so difficult?

    I thought the old rope and the new one were a bit different, the old one being smaller diameter. But, I thought the old one was worn down from use, and the new one was merely fuller because of being new. And, the new rope was off the same supply spool as I used for my Stihl BG85 blower last Fall.

    After much to do, I finally got it through the hole and fitted. Well, not exactly. The knot on the spool end would fit down into the channel as the old one. This was bothersome because I think the room is needed against the disk with the pall. However, I moved forward, and let the spool loose, allowing the spring to take up the rope. I had already tied off the handle.

    To my dismay, the handle would not fully retreat to the housing. The rope was filling the groove in the spool, and interfering with the edges. The handle was 3-4 inches away from being seated against the housing.

    Now, my suspicions about the proper rope are being fully realized. I took both pieces, the old spool with its rope, and the housing with the new spool and rope, back to the dealer. What is wrong in this picture? The counter person pulled out the spools of rope and we learned she had given me the smallest rope they have, #4. "... but this rope will not work...." She retrieved their mechanic, and he looked at it, "... rope is too big, give him a smaller one. But, we don't have anything smaller."

    I came home and looked in my catalogs of equipment (e.g. J-Thomas). They all show a #3 1/2. I called another equipment dealer, and he said they always string their trimmers with #3 1/2. I went over, picked up a new length of # 3 1/2 rope. Five minutes after returning to the bench, all was restrung and in order. The spool had plenty of room for all the length needed, the handle fully seated against the housing. And, it took me all of
    15 seconds to get the rope through the hole in the spool -- not the several hours with the other rope.

    Bottom line: Use #3 1/2 for Stihl trimmer starter rope!!! Don't let the dealer give you #4, telling you it will work. This advice is true for FS85, FC85, HS80. Undoubtedly, other models fit the category too.

    I have no explanation of why the dealer didn't have the smaller rope, and why they were perplexed by my concern. What do they do with a repair job that comes in the door? I don't know. The confusion cost me a couple of trips, and several hours of repair time. Oh yes, remember the Stihl BG85 used #4 rope.

    Maybe this is all common knowledge to most of you -- if so, my apologies for boring you. For those of you who do your own repair work and haven't encountered the problem, maybe this will be helpful to you at some time in the future.

    Also, interesting question: Why don't Operator manuals include the size of starter rope recommended for the engine of interest? I don't recall ever seeing it in the specification list. Is there a good list anyplace? I think my LawnBoy and Toro (Sizuki) must take #4, but I'm not sure. The 15hp Kohler takes something larger, but I can't give you a number.
  2. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    thanx for the heads up on this, I have 1 - fs85 and Im going to bookmark this thread for future reference

  3. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Wow, nice writeup but basically, use a #3 1/2 starter rope lol.
  4. lawnboy dan

    lawnboy dan LawnSite Gold Member
    Messages: 3,711

    this is exactly why i dont repair pull starters. i just get a new one.some repairs are simply not worth the trouble. i salute you for your persistance though.
  5. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,366

    Not really that complicated , just got to have some experience. Another good reason to buy Echo since they are definitely easier to work on.

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