In loving memory of Kenis D. Keathley 6/4/81 - 3/27/22 Loving father, husband, brother, friend and firewood hoarder Rest in peace, Dexterday

Straight gassed BR600

Discussion in 'Chainsaws and Power Equipment' started by basod, Apr 27, 2015.

Page 2 of 2
  1. AJtree88

    AJtree88

    Joined:
    May 15, 2014
    Messages:
    318
    Likes Received:
    1,764
    The problem with straight gassed 4-mix blowers is that the wrist pin seizes and takes out the crank since they don't use a roller wrist pin bearing like saws. It's just a tight fit like a plain bearing.
     
    AJtree88, Apr 28, 2015
    #21 Top
    Jon1270, rookie1, basod and 2 others like this.
  2. MasterMech

    MasterMech The Mechanical Moderator

    Joined:
    Oct 2, 2013
    Messages:
    9,648
    Likes Received:
    26,019
    Location:
    Greenville County SC
    That was really only an issue with early production units and was fixed with a material change early on. If you have a BR600 that's not a first year unit, it's most likely got the new valves. Was pretty nifty to see an exhaust valve stuck in the piston upside down like a daisy. :rofl: :lol:

    The other issue was with some commercial operators especially, they would over-rev/overheat the engine and it would slip the exhaust valve guide.
     
    MasterMech, Apr 28, 2015
    #22 Top
    XXL, basod and Fanatical1 like this.
  3. basod

    basod

    Joined:
    Nov 4, 2013
    Messages:
    5,048
    Likes Received:
    20,840
    Location:
    Mount Cheaha AL
    any recollection on first year unit production time frame?
     
    basod, Apr 28, 2015
    #23 Top
  4. MasterMech

    MasterMech The Mechanical Moderator

    Joined:
    Oct 2, 2013
    Messages:
    9,648
    Likes Received:
    26,019
    Location:
    Greenville County SC
    I knew somebody would ask me that. Lol

    I want to say 2006-7. I'm not sure. I could look at mine when I get home next week as its a fairly early unit.
     
    MasterMech, Apr 29, 2015
    #24 Top
    XXL likes this.
  5. basod

    basod

    Joined:
    Nov 4, 2013
    Messages:
    5,048
    Likes Received:
    20,840
    Location:
    Mount Cheaha AL
    This ones newer than that 2009-2010ish
     
    basod, Apr 29, 2015
    #25 Top
    XXL likes this.
  6. MasterMech

    MasterMech The Mechanical Moderator

    Joined:
    Oct 2, 2013
    Messages:
    9,648
    Likes Received:
    26,019
    Location:
    Greenville County SC
    Should have all the updates including the dual pickup fuel line. All early BR500/550/600 blowers had a tendency to starve for fuel with less than half a tank in them.
     
    MasterMech, May 1, 2015
    #26 Top
    basod and XXL like this.
  7. NewToStihl

    NewToStihl

    Joined:
    Apr 27, 2014
    Messages:
    807
    Likes Received:
    2,397
    Location:
    Central Indiana
    Some notes. First, you'll have to cast aside the "higher compression is better" 2-stroke mindset. The Stihl 4-mix engines aren't intended to have the high compression of chainsaws, and if I recall they have intentional/built-in decompression. My memory sucks, but I think the optimal range for them is somewhere around 115-125psi or something??

    Second, if you're looking for a replacement engine it's good to know that the BR550 and BR600 have the same engine, so your options are opened up a bit.

    Lastly, it's absolutely not a 4-stroke engine; it's a 2-stroke engine that has an exhaust/intake valve configuration that optimizes the transfer of fresh fuel intake and exhaust discharge. It still creates combustion each time the piston reaches TDC (i.e. 2-stroke). They called it a 4-Mix because of the valves. They no longer call it a "4-Mix", but rather a "low emission engine" or "reduced emission engine" or something like that. I'm told the name change was due to too much confusion between 4-cycle and 4-Mix and too many folks using straight gas. Despite the name and the valves, another reason I've noticed it's often confused as a 4-stroke is the lower RPM at WOT. It certainly takes some getting used to because they run several thousand RPM lower at WOT.
     
    NewToStihl, May 1, 2015
    #27 Top
  8. fox9988

    fox9988

    Joined:
    Oct 4, 2013
    Messages:
    2,709
    Likes Received:
    8,275
    Location:
    NW Arkansas 72717
    I haven't read about 4-Mixes in years, but I remember them being a 4 stoke= 4 strokes per firing, fire every other time the piston reaches TDC.
    The difference being: the crankcase lube is mixed in the fuel and circulates through the crankcase.
     
    fox9988, May 1, 2015
    #28 Top
    MasterMech likes this.
  9. MasterMech

    MasterMech The Mechanical Moderator

    Joined:
    Oct 2, 2013
    Messages:
    9,648
    Likes Received:
    26,019
    Location:
    Greenville County SC
    fox9988 is absolutely correct. The 4-mix is a 4-stroke engine with a total loss lubrication system. It runs the fuel mix through the crankcase like a 2-stroke but dedicates an entire stroke to suck, squish, bang, and blow.

    Some of the trimmer engines tach out to 10-11k RPM, which is plenty zippy. They just sound deeper and slower because they only fire half as often as a two-stroke turning the same RPM.

    They do indeed have a built in de-comp bump on the cam lobe. One cam lobe runs both valves due to the special geometry of the lifter arms.
     
    MasterMech, May 2, 2015
    #29 Top
    basod and fox9988 like this.
Page 2 of 2