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Thread: Petcock threads.

  1. #1
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    Petcock threads.

    I was wondering if there was a source for the thread size/pitch on the '70's R fuel tank fittings. A hose/fittings company says the male tank fitting is M20 x 1.0. I'm trying to find a solid end cap to be able to etch/tank seal. I see M20 x1.5 but no 1.0. Is this unique to BMW?
    Any help will be appreciated.
    Last edited by Danl; 04-11-2019 at 06:45 AM.
    Just an old guy here. Killin' bugs at a rapid pace since '68. Desert dweller.
    Current force: '77 R100/7 ,'85 K100RS-Aug84, '85K100RS-Aug84, '85 K100RS-June85, '93K1100LTSE,'93 K75LTP,'08K1200GT, (2)'72 CB 750s, '76 Honda CB500,

  2. #2

    Wine cork works just fine

    I shave down wine corks and stuff them in to do that.

  3. #3
    I just used rubber stoppers that I got at my local Ace Hardware store for the same purpose. Their fastener aisle (the one with lots of little drawers full of common, as well as fairly arcane hardware) had them in sizes to fit both the fuel petcock stubs, and the gas cap opening in my tanks. They held fine for the couple of hours I was sloshing Evapo-Rust around in my two tanks. I placed the tanks in a big plastic recycle bin when they were left to soak, just in case one of the stoppers decided to take a break, but they didn't leak a drop.

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    Stoppers

    Quote Originally Posted by khittner View Post
    I just used rubber stoppers that I got at my local Ace Hardware store for the same purpose. Their fastener aisle (the one with lots of little drawers full of common, as well as fairly arcane hardware) had them in sizes to fit both the fuel petcock stubs, and the gas cap opening in my tanks. They held fine for the couple of hours I was sloshing Evapo-Rust around in my two tanks. I placed the tanks in a big plastic recycle bin when they were left to soak, just in case one of the stoppers decided to take a break, but they didn't leak a drop.
    I never drank anything good that came in a container with a rubber stopper

  5. #5
    Quote Originally Posted by 179212 View Post
    I never drank anything good that came in a container with a rubber stopper
    That's certainly true, and even though the label claims that Evapo-Rust is "non-toxic", I still wouldn't drink it.

  6. #6
    Registered User lmo1131's Avatar
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    It's been at least ten years ago, but we had a salesman stop at our shop. Among other shop type chemicals he had Evapo-Rust on this truck. He went through his sales spiel and finished if off by taking a big slug of it out of a freshly opened bottle ... which I found to be thoroughly insane.

    I use rubber plugs from Ace as well.
    "It is what you discover, after you know it all, that counts." _ John Wooden
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  7. #7
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    Plugs

    Thanks for the feedback.
    It's not the etching that's an issue. I use a tank sealer called RedKote and the solvents build up pressure as I'm sloshing the tank and blows the rubber stoppers out. That's why I'm looking for full metal caps.
    Danl
    Just an old guy here. Killin' bugs at a rapid pace since '68. Desert dweller.
    Current force: '77 R100/7 ,'85 K100RS-Aug84, '85K100RS-Aug84, '85 K100RS-June85, '93K1100LTSE,'93 K75LTP,'08K1200GT, (2)'72 CB 750s, '76 Honda CB500,

  8. #8
    Liaison 20774's Avatar
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    How much pressure are you talking about? Any concern that a full cap on the entire tank will result in enough pressure to push the tank out of shape??
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  9. #9

    Red Kote is the best

    Don't go crazy with the etching stuff. I've done about 7 tanks with Red Kote and have used white vinegar to etch followed with an overnight hair dryer and then a M.E.K.(Methyal Ethal Ketone) rinse a day before I use the Red Kote. I use the wine corks and an old beat up lid to hold all the crap in.

    I would not use anything stronger than white vinegar to etch the tank and if you do the etching, rinse and sealing in a controlled (cool temperature) very little pressure builds up, use an old crappy gas cap and pop it open every so often during the rolling and manipulating part of applying the Red Kote.

    If your gas tank has good paint on it you should spend some extra time and effort to cover, mask or otherwise protect the paint because the M.E.K. and the Red Kote will take the paint right off.

    Much like paint and body work the preparation is the key to success and a nice job.

  10. #10
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    Petcock threads

    Thanks for all of the feedback. But I really want to find the caps. There's just enough pressure to pop the corks. And the caps would be just a lot more professional, especially on a painted tank.

    Phosphoric is my etch of choice.....we used it a lot on the aircraft.

    Danl
    Just an old guy here. Killin' bugs at a rapid pace since '68. Desert dweller.
    Current force: '77 R100/7 ,'85 K100RS-Aug84, '85K100RS-Aug84, '85 K100RS-June85, '93K1100LTSE,'93 K75LTP,'08K1200GT, (2)'72 CB 750s, '76 Honda CB500,

  11. #11
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    I have no idea on the threads. Most of the time I have to guess. To make it easier I will bring the part(s) with me to a local hardware store. Most of the local hardware stores have an assortment from “Midwest Fasteners” which get me through.
    With what you are doing, if I understand it correctly, you may be able to use a well shaped piece of pine and thread the pine in/on.
    OM
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  12. #12
    Quote Originally Posted by Omega Man View Post
    I have no idea on the threads. Most of the time I have to guess. To make it easier I will bring the part(s) with me to a local hardware store. Most of the local hardware stores have an assortment from “Midwest Fasteners” which get me through.
    With what you are doing, if I understand it correctly, you may be able to use a well shaped piece of pine and thread the pine in/on.
    OM
    Find a set of old sacrificial petcocks. Plug them with a cork disk from the inside. Screw them into place. Shake away. I am virtually certain you won't find a cap with that fine a metric thread at any common source for hardware in the US.

    Or remove the nuts from junk petcocks, weld or braze on a disk to close the bottom end and screw them into place.
    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
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