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Thread: How do you shrink a rubber gasket

  1. #1
    apriliaforum expert MauriceOz's Avatar
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    How do you shrink a rubber gasket

    OK, I was replacing the airboot with the Mille one and when I went to put the airbox top back on I had a rubber gasket hanging out.

    The last time this happened was on a different bike and the mechanic who was working on it said that he would have to shrink the gasket.

    So how do you shrink a rubber gasket, it was quite oily and I assume that the gasket has absorbed oil and grew, so how do I get it on a diet and make it fit again.

    Maurice

  2. #2
    apriliaforum expert Bikeaholic's Avatar
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    Maurice..........This happens on mine regularly. I imagine the only way to shrink is to cut it back so that it fits again and then super-glue the ends back together.

    Ages ago I ordered a replacement gasket through my dealer but instead of the finished product and got several meters of the correct size rubber O-ring. So now I simply make up new caskets as I need them.

  3. #3
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    Clean the oil from the o-ring and the o-ring groove using mild solvent if necessary. Tack a few spots of the o-ring into the groove with gasket cement. Then you'll see how much to trim to fit with it semi-installed.
    John

  4. #4
    apriliaforum expert Dan's Avatar
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    If it's rubber or plastic, try sticking it inside the freezer.
    If I just gave you mechanical, personal, legal or medical advice, it's up to you to get a proper diagnosis from a qualified expert.

  5. #5
    apriliaforum Member RSTinker's Avatar
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    I have the same problem with carb and brake rubber. The best way I have found is to clean off the oil with solvent and let it sit in the sun for awhile ( hour or 2) Good luck.

  6. #6
    apriliaforum expert bikpaintr's Avatar
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    I've had good luck shrinking large o'rings used to seal gas caps or fuel pump panels by boiling them in water. It sweats out the solvents & I am able to reinstall them without too much effort. Sometimes just cleaning them well & letting them sit around for a day or so will work but I usually don't have the time to wait. You can also cut out the excess & reattach the ends with superglue but I prefer to keep them intact.
    John B.
    02 Ash Black w/Staintunes, PC3 w/custom map, Evo Filter, Mille Air Boot, derestricted air box, Heli-Bars, Wilbers shock, new rectifier, Scottoiler, heated grips, T'meister, c/f frt. fender & hugger.

  7. #7
    apriliaforum expert Loch Rob's Avatar
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    Most gaskets or elastomers are manufactured with a specific durameter (or hardness) per a specification. These also typically have a "z" rating added to the specifications for material compatibility with gas, oil, phosphate ester (hydraulic systems), etc. I don't believe "shrinking" a gasket is possible.

    I don't recommend boiling or putting in the freezer as you could easily change the properties of the material (i.e. cracking, hardening, embrittlement, etc.). The plasticizers in the rubber can leach out causing application problems. Cutting and super gluing might be the best approach if there isn't oil or other material on the surface. Gluing an o-ring typically won't work as a long term fix. You might be able to glue a lathe cut, or square cut, gasket depending upon the application.

    My 2 cents, from years of working with elastomers.....
    Robbie

  8. #8
    apriliaforum expert bikpaintr's Avatar
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    Loch Rob - The o'rings sealing the gas filler assy on Oilhead BMWs always expands & is a bitch to get back in. Boiling them is common practice & works quite well to resize them. Just did it a few weeks ago on a 94 RS & have done it with others. Never had any problems with this procedure.
    John B.
    02 Ash Black w/Staintunes, PC3 w/custom map, Evo Filter, Mille Air Boot, derestricted air box, Heli-Bars, Wilbers shock, new rectifier, Scottoiler, heated grips, T'meister, c/f frt. fender & hugger.

  9. #9
    apriliaforum expert Loch Rob's Avatar
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    Hmm, interesting Bikpantr, seems a bit contrary. The boiling must leech out the oil the rubber has absorbed. Spec'ing out a compound with oil resistence would alleviate the swelling. Many are available, but finding the right size for the Beemer application could be a problem. Learn something new every day.
    Robbie

  10. #10
    apriliaforum expert vtwin_pilot's Avatar
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    Quote Originally Posted by Bikeaholic
    So now I simply make up new caskets as I need them.
    A freudian slip, I hope. Or are you an undertaker???

  11. #11
    apriliaforum expert RAS's Avatar
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    Maurice, same thing happened to me with that same Oring. I tried to reorrient it so that all the bends were in about the right place and then proceeded to hold it in place with one hand and then work it back into the groove. After a section was in, i kept pushing(sliding) towards the spot I was holding still. It took a while, a couple attempts, and a lot of compressing, but it finally went back in. I'll likely never remove it again unless i have a new one right there. Give it a go, be patient. rick

  12. #12
    apriliaforum expert MauriceOz's Avatar
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    Thanks Rick

    Thats basicaly what I did as the bike without an airbox cover is not an option.

    Thanks guys for all the other options, I guess I will be cleaning, heating, boiling and freezing until it either gives up the ghost or it fits.

    maurice

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