'O' rings

For discussions about bikes and equipment.
Brucey
Posts: 40465
Joined: 4 Jan 2012, 6:25pm

Re: 'O' rings

Postby Brucey » 22 May 2020, 12:43pm

Jamesh wrote:...what's the other hobby btw???...


for many years (not so much these days) I have messed about with cars and motorcycles. In my previous working life I worked closely with various vacuum systems.

Foghat wrote:Has anyone got a source of stretchy o-rings?

Most o-rings that I've found are not very stretchy at all, but the ones I wish to procure a spares supply for are really quite stretchy, which is a very useful feature. The stretchiness does, though, mean they are somewhat prone to breaking.

The particular stretchy size I wish to buy a plentiful back-up stock of is 42mm ID x 2.5mm CS. The ID could be both several mm larger or smaller and still work, but the CS probably needs to be no more than +/-0.5mm.


Most 'O' rings are sold as seals and only need to be as stretchy as is required for the sealing application (which is not very), and chemical resistance is more important. My guess is that you are after rubber rings to retain lights etc to handlebars. I confess I don't know what rubber grades are used in these rings normally, but I suspect it might be mostly butyl rubber with (hopefully) a cocktail of additives which are intended to make it weather resistant (a bit like tyres). Whereas O rings seem to be (if not specified eg in cheap boxes/kits) most commonly made in Nitrile rubber. So when I have needed these rings, if O rings are not stretchy enough I've bitten the bullet and bought the right thing even though it cost more than I'd like.

Further to the original post above, I have discovered that at least one of my many boxes of cheap O-rings contains seals made in a rubber grade that deteriorates quickly in external conditions. The thing is, I'm not sure which box; I have used many O-rings from several cheap kits to replace the seals in PD-M324 and PD-M323 pedals; you need four at a time (for a pair of pedals) and I remember having to take three from one box and one from another. The 'odd one' perished in less than a year and the other three are still fine. Obviously I don't recall which box the rogue O ring came from.... :roll: Needless to say I'm now worried that I might have used (or will use) an O ring from that box (whichever it is) which might turn into a big problem.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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NATURAL ANKLING
Posts: 12092
Joined: 24 Oct 2012, 10:43pm
Location: English Riviera

Re: 'O' rings

Postby NATURAL ANKLING » 22 May 2020, 3:36pm

Hi,
Old story.
I brought a brand-new motorcycle and six months later two small bellows made of rubber had perished.
I brought some replacements and fitted them bearing in mind the bike was brand-new, the new ones lasted 10 years or more.
So bad batch of rubber or when I fitted the new ones I probably would've use some rubber grease on inside of bellows.
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.

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Foghat
Posts: 101
Joined: 19 Mar 2013, 10:44pm

Re: 'O' rings

Postby Foghat » 23 May 2020, 9:45pm

The rings are for mounting computer sensors to fork legs, Brucey, where the stretchiness is essential due to the taper of the tube and to the awkwardness of installation.

As it happens, it occurred to me that the rubber bands Garmin fits to its quarter-turn mounts could be a similar size to what I need....and somewhat fortuitously it turns out that the two Garmin sizes are exactly the same as what I'm after (ID and CS). And since I stocked up with plenty of Garmin spare bands a few years ago, I've actually got a ready stash to tap into.....and of course I now know of a continuing source too. Garmin's bands are pretty stretchy EPDM.

Your degrading o-ring problem - is that your EPDM ones proving more resistant to weathering/sunlight/ozone than your nitrile ones?

Brucey
Posts: 40465
Joined: 4 Jan 2012, 6:25pm

Re: 'O' rings

Postby Brucey » 23 May 2020, 9:56pm

Foghat wrote:The rings are for mounting computer sensors to fork legs, Brucey…


not far off....

Your degrading o-ring problem - is that your EPDM ones proving more resistant to weathering/sunlight/ozone than your nitrile ones?


I don't know for sure but I don't think either sort (good or bad) was EPDM; EPDM tends to swell up in the presence of many lubricating oils, and these hadn't swollen, despite being rather oily.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~