75/5 Leaking Bings fixed.

Discussion in 'Airheads' started by patanga, Jun 29, 2012.

  1. patanga

    patanga BMWAirheadsDownunder

    Joined:
    May 10, 2009
    Oddometer:
    164
    Location:
    Australia
    Have been dealing with a set of persistent leaking bings on a 75/5 and after checking all of the usual suspects I decided that the 40 year old needle seats would likely be worn and that the carbs might benefit by replacing them. Thought I'd share the procedure I use for anyone faced with similar symptoms. Nb: While this repair isn't overly difficult, if you're not confident, leave it to your repair specialist. Dealerships and most parts houses will tell you that the brass needle seats are not available and to replace the carb body.. Replacement seats can be bought direct from Bing USA.

    I am advised that it is also possible to upgrade the /5 bings (steel needles) to take the later model rubberised needle and seat. If that's the preferred option then the floats and retainer clip will also need to be replaced. (haven't tried this later upgrade myself self yet so I take no responsibility for the accuracy of that advice)... This repair was for a 75/5 but the same procedure applies to all Bing carbed airheads. The only exception on the later models being the size of the thread tap required.

    Tools & bits required.
    [​IMG]

    The seat in question
    [​IMG]


    Cutting the thread for puller tool (M7 x 1 tapered tap, or even better an M7 x .75 if you can find one) Make sure to check the alignment of the tap as it is cutting the thread. Hold carb body upright while thread is being cut to minimise the risk of brass scrap from falling into the carb.
    [​IMG]


    Shop made puller tool (I use an old plastic bush as it is soft on the carb body. A similar sized nut will also do the job)
    [​IMG]

    Extractor sleeve fitted over old seat. (Nb: Sleeve must be longer than the seat and the I.D. must be larger as the old seat will be pulled up inside the sleeve.)
    [​IMG]


    Extractor tool fitted and ready to pull the 40 y.o. old needle seat.
    [​IMG]


    Extracting the old seat. (Nb: Disassemble a couple of times during extraction to ensure that the seat is clearing the sleeve as it starts to move and to check that it's being removed properly.)
    [​IMG]

    Old seat removed.
    [​IMG]


    New seat with a light coating of never seize lube. Shrink brass seat by putting in a freezer for a bit prior to fitting.
    [​IMG]


    Gently tap the new seat into place using a wooden dowel & small hammer. Note tape over the end of dowel to prevent bits from shedding into the seat. A plastic or brass drift will also do the job. Avoid using a steel drift as such could distort/damage the softer brass seat. If all you have is a steel drift then cover the end in a couple of layers of racing tape to make it softer than the seat. (Nb: The brass seat is a light interference fit and shouldn't be too tight to extract or fit.)
    [​IMG]

    Reassemble & tune the carbs. All other things being in order, leaking carbs should be a thing of the past. (That said, never trust old Bings not to leak.)

    Good luck.

    ____________________
    "The only reason people get lost in thought is because it's unfamiliar territory" (Joe Garcia)

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    #1
  2. Padmei

    Padmei enamoured

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    Good stuff. thanks for taking the time bro.
    #2
  3. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Why use anti-sieze ("never cease") on the new insert?

    Heating the carb body with a heat gun while removing the old and installing the new seat will greatly reduce the pot metal's (Zn-AL alloy) grip on the insert.
    #3
  4. sdduke

    sdduke David in Atlanta

    Joined:
    Apr 11, 2011
    Oddometer:
    347
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    Norcross GA
    Cool! I will try this in the winter.

    Thanks for the post.
    #4
  5. Wdwrkr

    Wdwrkr Long timer

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    Nice clear instructions, thanks. I'm gonnal print this one out for my folder of things to do

    Pete
    #5
  6. ME 109

    ME 109 Long timer Supporter

    Joined:
    Jun 25, 2009
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    Location:
    Albury Australia
    Did much the same for my bings, except I used a threaded sliding hammer arrangement to remove the seat.
    Tapping the seat would appear to be the only 'safe' way to do it.

    To insert the new seat I froze the seat and heated the carb body.
    #6
  7. patanga

    patanga BMWAirheadsDownunder

    Joined:
    May 10, 2009
    Oddometer:
    164
    Location:
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    Most things BMW, (i.e. where there is and interference fit) require heating prior to removal. That said I've not found the needle seats to be a tight enough fit for that to be necessary. I generally don't like heating carb bodies if it can be helped, just in case it distorts. If the seat is stuck fast and the carb requires heating then I'd recommend putting it in hot water for a while so that it heats evenly. After that, a quick shot of freeze spray in to the old brass seat and it should just about fall out. Make sure the body and fuel passages are thoroughly blown clean with air afterwards to remove any water residue..... Regards the 'never seize' (thanks for the spelling tip Bill. I missed that one until a later read.) I only use that stuff because of the two dissimilar metals and to aid a little in the fitment. Is it a must? not really. Just something I like to do in this instance.

    ____________________
    "The only reason people get lost in thought is because it's unfamiliar territory" (Joe Garcia)

    Check us out on facebook at "BMW Airheads Downunder", (The Australia and New Zealand Airhead Community). "B.A.D" :wink:
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    #7
  8. Disston

    Disston ShadeTreeExpert

    Joined:
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    Location:
    Silver Spring, Md
    I have to do this soon. Thanks. I also will use a bit of heat I think as Bill said. It may not be needed but I'll feel better.
    #8
  9. patanga

    patanga BMWAirheadsDownunder

    Joined:
    May 10, 2009
    Oddometer:
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    Location:
    Australia
    Hi disston. Using a threaded bolt extractor applies smooth even pressure. If you want smaller increments of extraction pressure you could try an M7 x.75 tap (finer thread, but not a common pitch held in tool supply stocks). This type of puller will give you good feedback to help you decide if additional heat is needed. That said; To heat or not to heat, is your call :)

    ____________________
    "The only reason people get lost in thought is because it's unfamiliar territory" (Joe Garcia)

    Check us out on facebook at "BMW Airheads Downunder", (The Australia and New Zealand Airhead Community). "B.A.D" :wink:
    http://www.facebook.com/groups/anzairheads/
    #9