Replacement for cracked F8 fuel tank

Discussion in 'Parallel Universe' started by BykMyk, Mar 17, 2010.

  1. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,539
    Location:
    The great state of confusion
    Just one note of caution. When working around fuel systems be careful of sparks.
    Catastrophies are very rare, but having seen one in a garage I worked in many years ago ...
    I never want to see another one. :cry

    I have a piece of brass rod that I use when I need to "persuade" something tied into a fuel system.
    Copper and alloys containing copper (brass, bronze, Monel metal (copper-nickel alloy), copper-aluminum alloys (aluminum bronze), are all non-sparking. A hunk of copper water supply pipe can usually be found without much trouble.

    I'll be the first to say that the risk is very small, but if the tank went boom it would really screw up the rest of your day :lol3
    #41
  2. twizted1

    twizted1 Adventurer

    Joined:
    Jun 25, 2008
    Oddometer:
    77
    Location:
    Mid-Tenn
    After seeing these pictures, the tank is a one piece design. The white & black that you are seeing are merely different layers of the tank which is very likely blow molded. The white is likely going to be virgin material with no color added, the black is likely virgin and reground material with color added. If the tank design/fab is similar to the tanks that I worked with at a fuel tank manufacturer will be multiple layers of material with a layer of less permeable material sandwiched between the inner and outer layers of material.

    If the tank is of the construction I am describing, there is no separation between the white & black material shown in the picture.

    *former engineer at a fuel tank manufacturer
    #42
  3. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,539
    Location:
    The great state of confusion
    Cool! An expert! :clap

    So is a crack that starts in the outer black layer of the tank likely to stop at the interface, or at least be slowed down, due perhaps to the layer of less permeable material between the inner and outer layer?
    Is the less permeable material (in between) just a coating or does it have some real thickness to it that you could see if you examined the tank closely?
    #43
  4. runnin4melife

    runnin4melife Been here awhile

    Joined:
    Mar 23, 2012
    Oddometer:
    806
    Location:
    "No shit when I was back at Bragg!!!"
    So why are they cracking? :rofl
    #44
  5. twizted1

    twizted1 Adventurer

    Joined:
    Jun 25, 2008
    Oddometer:
    77
    Location:
    Mid-Tenn
    I've not been in the industry in 5 years now...but from the best of my memory, the layer thicknesses were dependent on the customer requirements and testing. A crack that started in any layer would eventually propagate through. The crack may "stop" for a time, but will eventually crack the next layer.

    All my input is based on the one company I worked for in the fuel tank industry, BMW's tanks may be built/designed/molded in a different process or using different materials than I have experience with.
    #45
  6. itsatdm

    itsatdm Long timer

    Joined:
    Jun 19, 2004
    Oddometer:
    5,273
    Location:
    Nor Ca.
    Do you have a guess as to the type of plastics being used? My plan, if this reoccurs and not covered by warranty, was to find an appropriate glue and fill in the crack.
    #46
  7. EPMD

    EPMD Been here awhile

    Joined:
    Mar 25, 2012
    Oddometer:
    205
    Location:
    Seattle, WA
    I recently bought a used 09 that was out of its 3 year warranty. I only noticed the cracking a couple weeks ago and took the bike to my local BMW dealer.

    The guy knew all about the issue and said it's covered for 5 years. It's currently being fixed and BMW will be paying the bill.

    It's taken about 1.5 weeks to get all the parts needed for the swap.

    The guy at the shop said the new part number is the same as the old part number so most likely it will just happen again a couple years down the road. That being said, to date no one has reported leaking fuel from these cracks so yes, it is purely a cosmetic issue.e
    #47
  8. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,539
    Location:
    The great state of confusion
    Thanks, so it sounds like ... given enough time
    This would move from being simply a "cosmetic" issue into a full-blown holy-crap my tank is leaking issue :cry
    Not cool, not cool at all ...........
    #48
  9. twizted1

    twizted1 Adventurer

    Joined:
    Jun 25, 2008
    Oddometer:
    77
    Location:
    Mid-Tenn
    From the pictures I've seen the cracking is at an interior angle (on the outside of the tank), those areas were problem areas for the mfg I worked for as locally thick spots, which was never as bad of a problem as locally thin spots. The thicker spots may not flex as well as the thin spots and crack rather than flex. Angles such as that though are also stress risers and as such will typically fail before the areas around them.
    #49
  10. twizted1

    twizted1 Adventurer

    Joined:
    Jun 25, 2008
    Oddometer:
    77
    Location:
    Mid-Tenn
    My thoughts would be HDPE, but I cannot recall what adhesive is used to adhere the middle layer to the HDPE.
    #50
  11. COracer

    COracer Adventurer

    Joined:
    Jan 6, 2011
    Oddometer:
    58
    Location:
    Co Lo Rado
    Thanks EPMD, sounds like a visit to the dealer might not end in tears so I'll start there.
    #51
  12. mbonadio

    mbonadio Adventurer

    Joined:
    Nov 3, 2012
    Oddometer:
    25
    Location:
    Phoenix, AZ
    Had the warranty repair on my 2 month old bike done yesterday.. Same part number tank installed. Dealer said 'it will probably crack again". Seriously? This issue is 2-3 years old and BMW hasn't recified it yet? I Again, I'm sure not that excited about the long term viability of this bike...

    But for the next few years while covered under warranty I do enjoy riding it... so that's what I'll do. But you can bet I'll probably sell it after 3 years before it cracks again. No way I'm paying $1800 bucks for one later!

    Although I'm told the cracks are just cosmetic. Yep, so is my wallet BMW!

    #52
  13. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,539
    Location:
    The great state of confusion
    The problem has been around since this bike was introduced.
    I have one of the early / VIN first-production year bikes
    I am on my 2nd tank which is also cracking slightly.

    If I understand correctly:

    1) original warranty is 3 years on entire bike

    2) since tank is part of fuel/emission system it may actually have a 5-year warranty

    3) any part replaced (under warranty or otherwise) has a 2-year warranty ON THAT PART
    I had my tank replaced just before the 3-yr factory warranty ran out.
    I expect to be showing up at my dealer just before the 2-year part warranty runs out...
    will expect my replacement tank will be free.
    I will also be hoping that by then the problem has been properly addressed!

    If not I guess I'll be back yet again in another 23 months? :lol3
    #53