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Stihl BG85 - sharper sound

Discussion in 'Mechanic and Repair' started by Roger, Nov 21, 2006.

  1. Roger

    Roger LawnSite Fanatic
    Messages: 5,943

    I have a Stihl BG85 hand blower. It has been used for at least four seasons, maybe five. In the last few days, the sound has been getting sharp. I don't know that I can explain it any other way. Clearly, it is louder, but am not clear if the difference is in the exhaust or something else. The sound is not a knocking, so it does not sound "internal."

    Each season, I mow about 1,100 or 1,200 properties and use it for drive and walk cleanup after mowing. And, in the Fall, it is used heavily for leaf cleanup. This season, it has been used more than others, some days working through 3, 4, or maybe even 5 tanks of fuel (runs about 45-50 minutes on a tank).

    It runs fine, it starts fine, with no difference in performance.

    I am wondering if the muffler has developed a hole or extraneous passageway. I have checked and the muffler is not loose. I keep thinking the sound difference is exhaust related.

    During the mowing season, when it was used for mowing debris cleanup, the baffles on the exhaust opening of the muffler were black. However, now that it has been run hard recently, the baffles are clean. There is no sign of carbon blackening.

    Anybody have any ideas on what to check?
  2. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    maybe something rubbing on the fan? maybe the fan itself?
  3. Roger

    Roger LawnSite Fanatic
    Messages: 5,943

    khouse ... I thought about that, but the sound is too consistent, it never changes. I have time tomorrow, and will be taking off the covers to check for that possibility. Thanks.
  4. Roger

    Roger LawnSite Fanatic
    Messages: 5,943

    My worst fears came to fruit about 10 minutes after starting this morning. The blower started well as usual, but soon thereafter stopped, never to run again.

    It just died while working at WOT. When I cranked, it had little, or no, compression. I took out the spark plug. The color was unusual, a reddish-brown, a burnt orange color. I cleaned it up and put it back. However, when I pulled the cord, it was nearly seized -- very hard to turn.

    So, I'm unsure what caused the fatal blow. When I was doing the initial start, I took a little time to pull the cord slowly a few times. I could hear a tick-tick sound on each revolution. I felt this was probably good information, and may have indicated the problem was something worn in the starter assembly. Also, having heard the sound on slow revolutions while just pulling the cord, that eliminated the exhaust/muffler as a source of the sound. The engine wasn't yet running, so the sharp sound was eminating from some other source.

    I set it aside and probably will take time in the offseason to pull it apart to learn more about what happened.

    I did immediately go to a dealer and buy another one, exactly the same blower. It is a BG85, model C. In another thread, I read speculation that only a model D (with cat converter) was now available. Such is not the case, at least in these parts. Maybe model D with cat converter is only sold in certain states.

    Just for your information, I have ran this blower nearly its full life on synthetic 2 cycle oil. I ran a couple of years with Amsoil, but the last two years, Opti-2, mixed 80:1.

    I have a Stihl FS-85 string trimmer running out of the same cans over the life, and the trimmer has probably run more service hours. However, rarely is the trimmer run for long periods of sustained WOT.
  5. S man

    S man LawnSite Gold Member
    Messages: 3,562

    That's strange. Is the new one working good for you?
  6. newz7151

    newz7151 LawnSite Silver Member
    from Tejas
    Messages: 2,419

    Amsoil can say what they want.. but unless the manufacturer has specifically tested that oil, and at that ratio, if I were you I'd run only Stihl oil mixed at the spec. ratio while you are in your warranty period on the new one.

    But, I'm not you, so do whatever in the heck you will.
  7. S man

    S man LawnSite Gold Member
    Messages: 3,562

    I agree with you. I had a ayp blower and ran 50:1 instead of 40:1 like recommended, and killed the engine the same day.
  8. Roger

    Roger LawnSite Fanatic
    Messages: 5,943

    On the oil issue, ...

    The recommended mix is 100:1. I ran that mix in some other equipment for most of a season, and decided it was too lean. No, I don't have a good and objective measure, other than it "sounded loose." There are plenty of other posts on LS that speak about running 100:1 for years, without problem.

    The reason I changed to synthetic was exhaust port buildup with other oils. My former blower eventually died because of too many disassemblies of the unit to clean the exhaust ports. The screw holes became loose due to the many cycles of steel bolts on aluminum screw threads. After switching to synthetic, I never had an exhaust port problem on the blower, or any other 2 cycle piece.

    In all fairness, I am not displeased about the longevity. It ran for many years of hard use. We do not use a backpack blower for leaf cleanup. All the beds, plus other places are blown clean with the hand blower. For the past six weeks (just like other seasons), it has been run WOT for long periods of time.

    All options for failure are open. But, based upon my experience with other 2 cycle products, I don't think synthetic oil is a culprit. I am going to run Stihl 50:1 in the new one for awhile, at least until it has a few months of service. I hope that I don't have exhaust problems.
  9. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    mercedes, lexus and many high quality and high priced autos now come from the factory with synthetic oil in them with scheduled oil changes at 15,000 miles plus. Amsoil has said this for around 30 years. I have ran Amsoil two stroke oil since the mid 70's without any problems. I run it in my Honda Pilot and change the oil every year. The early two strokes were 16 to 1 ratio. Who would run that now? There are some people that like to do exactly what the owners manual says. That's OK. But if you did that you would go the the dealer to buy Ford or GM oil, clutches, spark plugs, air filters ect. cause the manual says to do it. We all buy aftermarket parts. I choose to run synthetic oil. If you choose to run fossil oil that's OK.
  10. S man

    S man LawnSite Gold Member
    Messages: 3,562

    50:1 is the best way to go.

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