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I know they aren't, in reality, but the question is are the ones in suspension forks anything exotic, or can I use any old thing I find in B&Q?
Hopefully, got a massive box of them in Lidl this morning for a fiver
http://www.lidl.ie/en/Offers.htm?action=showDetail&id=20040
Got any that fit the inside of the PAR piston in 2007 Marzocchis 66s?
no they are not all the same.
If it was me and they were just holding oil and the dimensions were the same (thickness of the rubber is the important one, 3mm is very different to 1/8" in the world of an O ring) I'd be trying it.
If they are in with antifreeze and other things like high pressure and high temp etc. then it makes a difference.
Not using the right o-rings...
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Different materials for different applications. Different shores hardness, shear strength etc.
No.
Most common is Nitrile (NBR) for normal use (-5c - 80c)
Viton (FKM) for higher temp (-5 - 120c)
Silicon is for ok for very low / high temps but have no strength, & wear out quickly.
Posher compounds like HNBR, Suoer HNBR ok at low temps, but typically the lower the temp the softer the hardness, 60 for down to -40c, & higher temps you'd go for probably 80 - 90 shore.
EPDM is another but not compatible with oil.
Few expensive options also, like dual compound, hollow section etc.
Majority conform to some old BS tables for sizes metric & imperial sizes, but there is also an European metric table.
Will the ones sold for plumbing purposes be destroyed by fork oil, then?
Doubt it, more likely to be Nitrile.
Anything other than EPDM would be ok.
So, wait.. If nitrile is only down to -5c then biking in really cold weather could affect your forks?
Depends on the sort of nitrile. 'Medium' acrylonitrile content nitrile rings (the most common kind) would normally be good down to -20C so I wouldn't worry too much. I'd be more concerned about about the oil resistance of the really cheap kinds... You really do get what you pay for with elastomers 🙂
I don't want to disagree with Takisawa2 but hardness and low temperature flexibility aren't the same thing although I might be misinterpreting what was meant as plasticisers are frequently added to improve flexibility and they do tend to reduce hardness.
If you're really bored have a look at this paper I co-authored a few years ago...
What size you after molgrips...?
Don't know, and don't know how to measure it either.. I replaced with the wring size, and cannot find the original. Will have to search for a part list or something after the rugby.
Usually specced ID x cross section.
Have used Simplybearings a few times, they are good.
But try & measure, we have lots of sizes.
3/32 looks the right thickness.
We have to use 90 shore Nitrile in the ring main at work - mineral oil at 4000 psi. We only have to specify different materials for some of the funny non-flammable aviation hydraulic fluids. Sounds like plenty of knowledgeable people ^
However shore hardness doesn't tell the whole story - we have a couple of rubber balls to demonstrate - both measure the same shore, but drop them and one is like a billiard ball and the other a bouncy ball.
AD, you still at James Walker? I'm up at JW Devol.
Rob
🙂 Yep - small world. I run the material test labs down here - drop me me an e-mail/call on Monday if you like - it'll be good to put a face to a forum name 🙂
I'm actually coming down to Cockermouth on Wednesday!
rob.cooksley@ (you know the rest)
🙂
Molgrips, not sure if this helps or not, but I bought a pair of 55 ATA2 forks 2nd hand and the travel was stuck down due to air escaping into the -ve chamber of the ATA cartridge, which was a common problem with the 2009 range due to dodgy o-rings according to a forum post at MRB.com
Anyway, having got the required o-ring size (or one that was nearest it) I took a punt at the following item on eBay:
This size fitted the main air piston in the ATA cartridge really well, and 12 months on, still works perfectly, no loss of air and the travel stays up at 160mm. So it basically cost me 15p to fix, and to answer your question, I can only assume that the '70 Shore Nitrile' material these claim to be made from is good enough, and clearly better than what Marzocchi were fitting themselves 5 years ago 😉
Thanks 🙂 think I am going to call Windwave on Monday..
takisawa2 - had a reply from WW, the size is 18.70 x 2.62
Got anything?
Dude! DiscJockey has posted a link to exactly that 2 posts up.
Have another coffee
True, but that's the wrong size anyway - I forgot to edit... the size WW gave me was the external o-ring, I wanted the internal one. But I think 2.62 is my cross section.. just going to have to measure my shaft.
Opened thread, scrolled to bottom, read last sentence of last post. Won't be doing that again.
Yep, different materials/etc for different applications.
We have to use neoprene O-rings at work as refrigeration gasses and oils eat through other rubber materials.
ID + cross section is the best method to measure it.
Does anyone know what material the o-rings used for computer mounts and such are made of?
They're stretchier than the ones from my cheap o-ring assortment.
Not sure, but I just secured a crud catcher to my wife's bike with two DSG oil filter seals from the Passat.