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Thread: Leaking k75s fuel tank

  1. #1
    Broadstone
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    Leaking k75s fuel tank

    I bought a very high mileage K75S with a leak at the bottom front left edge of the fuel tank. I've had many motorcycles over the last 45 years, several of which had leaks, but they were either steel or fiberglass and were repaired with limited success. I had a leak in the tank of a K1200RS but I opted to buy a new one at significant cost and I'm trying to avoid a major cost with this 20+ year old bike so am asking for advice. Is there a repair kit available besides the liner kits or is it best to have it welded? If welding is feasible and I do it, I suppose I'd have to treat the inside anyway. If I do that and/or buy a used one, has anyone had success buying matching paint (pearl white) to refinish the exterior of the tank. Any advice will be greatly appreciated.

  2. #2
    Registered User kgadley01's Avatar
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    I had one leaking in the same area on a 91 K75 I used to have. I drained the tank and cleaned the area. I then mixed and applied some JB Weld. It worked like a charm and never leaked again. If you decide to use this method, be sure to leave the gas cap open during the drying time.
    AKA SNAPGADGET
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  3. #3
    BMW uber alles! Zagando's Avatar
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    Exclamation Easy, cheap and permanent fix:

    I also had a couple of pinhole leaks that I discovered when I was stripping and polishing my tank a couple of years ago.

    The holes are caused by water that collects in those low corners that eventually corrodes the aluminum.

    My solution cost me $3 at Home Depot (although nowadays the cost is more like $5 due to inflation)---FastSteel epoxy steel putty that comes in Tootsie Roll form over in the Adhesives section of Home Depot.

    I like this stuff much, much better than JB Weld.

    Twist off how much you need, knead it in your hands for about two to three minutes (use nitrile gloves) until it starts to noticeably warm up, apply to the cleaned -up area with the leaks and presto! No further leaks and it sets rock-hard in 5-6 minutes flat.

    I also use it around the house for all kinds of fixes as well as in my lapidary work (backing thin pieces of turquoise for cutting); it's good to have on hand when you're on the road, too (like a solid duct tape/baling wire in a tube).
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

  4. #4
    Dale Rudolph
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    I also had a pinhole leak in the same spot on my 1992 K75RT. I used JB Weld, It has been over 1 1/2 years and has done it's job.

    I repaired it while leaving the tank on the bike. The problem with doing this is that every time you think you have every last drop of gas out of the tank, some more gas ends up
    dripping out of the pinhole.

    It took a while to realize it was happening because the place where the leak was is the very lowest part of the tank where the pick-up to the fuel filter is. Any fuel that is in the filter will eventually drip out of the pick-up tube.

    If I had to do it again, I will remove the filter and while it's out, replace it.

    The nice thing about it being an RT model is the JB Weld repair is completly covered by the fairing.

  5. #5
    Broadstone
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    92 k75s fuel tank leak

    Thank you both. I will try one of these fixes and assume the repair needs to be from the inside. The guy that I bought it from tried some sort of epoxy stuff but only on the outside and it started leaking again after I filled the tank.

  6. #6
    Dale Rudolph
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    broadstone;
    Others may have done it on the inside, I put the JB Weld on the outside and as I stated, it has never leaked again.
    The two holes I filled were no bigger than a pinhead and I assume they had just started to leak.
    It could be that what the previous owner used was not intended to be used in contact with gasoline.

    There are coatings that are used to line the inside of the tank, I think one brand is called POR.
    You might Goggle " sealing a gas tank" to get some info on these products.

  7. #7
    Registered User kgadley01's Avatar
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    I also repaired mine on the outside.
    AKA SNAPGADGET
    Lifes too short to ride an ugly Motorcycle

  8. #8
    Broadstone
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    K75 leaking gas tank

    I have to remove the tank anyway because the leak is behind the fairing so I guess I'll repair it inside and out. My leak is MUCH more than a pinhole so it may be take a bit more attention. Thank you for your input; I'll start on it tomorrow and,to be on the safe side I might epoxy the length of the bottom edge in case another leak is close to happening in that area.

  9. #9
    BMW uber alles! Zagando's Avatar
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    I removed my tank, drained the tank and carefully cleaned and sanded the area to be sealed. Yes, I made sure there was no dust inside the tank and even cleaned the inside to make sure.

    Once dry I applied the FastSteel to the outside only and covered an area much larger than the actual leaks. Two to three years now and not a single problem since.
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

  10. #10
    Mars needs women! 35634's Avatar
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    I used JB and it lasted a couple years, then tried this, been good so far. Available most auto parts stores.
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    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  11. #11
    Registered User
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    You could take it to a gas tank or radiator repair place. They could solder it up or they can pour sealer on the inside of the tank. I don't think a motorcycle tank would cost that much.

    David Sword

  12. #12
    BMW uber alles! Zagando's Avatar
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    Fast Steel=$5.00 Done.
    ---Jeff '94 K75S Berlina

    ex: R100GS/PD , K100RS , R75/5 , R60/2

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