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Thread: 85 K100 RT Stuck Fuel Cap

  1. #1
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    85 K100 RT Stuck Fuel Cap

    Hi All,

    I'm looking for tips, tricks and insight into how to convince the fuel cap on my 85 K100 RT to open.

    I had no trouble with it a few days ago, so there is no history of it sticking or being difficult to open.

    Turning the key counter-clockwise has resistance from the spring and will return mostly to center. However the latch does not seem to release to allow the cap to open.

    I've read snobums article on drilling or using a dremel to gain access to the sliding part of the latch for cases where the key has broken off. (http://bmwmotorcycletech.info/fuel-caps-airheads-K.htm)

    I'm hopeful that there are other options to investigate first.

    Thanks in advance.

    Monte

  2. #2
    Try pushing down on the cap firmly while turning the key. Maybe? Maybe not?
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
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    After researching and reading numerous posts of a similar nature, I'm still confused - go figure.

    Most of the lock failures that I found were that the knobs on the bottom of the key cylinder corrode away and allow it to spin without rotating the cam to move the sliding latch. The spring to return the key to center is located under the cam.

    Since my key does not rotate freely and returns to center, I can only presume that the key cylinder is connecting and making contact with the moving parts. It just doesn't move the latch enough to open the cap. - Weird -

    Capture.jpg

    I plan to push and pull while turning the key with the hope of getting lucky, but it's starting to look like I need to sharpen a drill bit.

    Expert guidance is always appreciated.

    Monte


    Links for the best information that I've found.

    http://www.k100-forum.com/t9469-open...-a-broken-lock

    http://www.k100-forum.com/t4418-fuel...ing-and-repair

    http://bmwmotorcycletech.info/fuel-caps-airheads-K.htm

  4. #4
    Registered User 6322's Avatar
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    If it was functioning fine a couple of days prior, could it be a vacum problem like maybe the vent hose is plugged not allowing the pressure in the tank to equalize so the negative pressure is holding the lid shut? Mr Glaves, what do you think? If this is the case, may a little air in the vent hose would clear it.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  5. #5
    Quote Originally Posted by 6322 View Post
    If it was functioning fine a couple of days prior, could it be a vacum problem like maybe the vent hose is plugged not allowing the pressure in the tank to equalize so the negative pressure is holding the lid shut? Mr Glaves, what do you think? If this is the case, may a little air in the vent hose would clear it.
    Good thought. A real possibility.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  6. #6
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    Quote Originally Posted by 6322 View Post
    If it was functioning fine a couple of days prior, could it be a vacum problem like maybe the vent hose is plugged not allowing the pressure in the tank to equalize so the negative pressure is holding the lid shut? Mr Glaves, what do you think? If this is the case, may a little air in the vent hose would clear it.
    Good thought - I'll give that a try next.

  7. #7
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    Update

    I was able to rule out the vacuum lock/blocked vent by connecting a hose to each of the lines on the bottom of the tank. Both were clear. The cap drain let air pass freely. The tank vent took a reasonable volume of air and expelled it with the added aroma of gasoline.

    I proceeded to phase 2 and followed the instructions to drill a hole 23 mm from the hinge of the cap. Started with a 1/8" then switched to a 3/16 (apx 5mm) to make a hole large enough to work through. Used a pick and was able to retract the latch as described in the previously posted links.

    Upon disassembly I found that one of the two catches on the bottom of the lock cylinder had broken off.

    Next steps are to find a 5mm rubber plug and replace the lock cylinder.

    At least for now, I can add fuel to the tank and keep riding.

    Thanks,
    Monte

  8. #8
    Registered User 6322's Avatar
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    Thanks for the update Monte. Sorry it was a mechanical versus a vacum problem. At least your closer to the fix than the problem.
    gp
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  9. #9
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    Sorry for the late follow up, but life got busy and I've just found the time to finish rekeying and installing the new lock cylinder.

    Here's a pictorial recap for anyone that wants to see what the post was all about.

    Thanks again for the advice and guidance.

    Monte

    85K100FuelCapRepair-sm.jpg

  10. #10
    RK Ryder
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    Thank you for the above link. I may have to do the same as there is nothing inside the cap (where the lock cylinder sits) for long nose pliers to grab. After reading the link in the previous post, that looks as if that will be my alternative.

    I had a gas fume issue with my '87 K100 for 15-20 minutes at the beginning of each ride. After removing the gas tank and finding that the hoses were secure, including the vent hose and the rectangular funnel device (called an air accumulator) was in place, I decided that maybe the odours were escaping from the gas cap, which after 32 years and 166,000 miles, had rotten looking gaskets and washers. Hence that is what I replaced yesterday.

    Since today is one of the few dry, sunny and warmish days this spring, I think I'll go for a ride on the 1100 this afternoon and get back to this later.

    Again, thank you for the link for opening the cap (without a key).
    Attached Images Attached Images
    Paul F. Ruffell
    Retired and riding my RTs, the '87 K100 & the '98 R1100 !
    Niagara Riders & Knights of the Roundel #333

  11. #11
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    Glad it helped.

    Since your lock cylinder is out, maybe you won't have to drill.

    Try using long nose pliers to turn the mechanism and actuate the latch.

    Best of luck!

    Monte

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