O-rings – talk to me

These bloody Marzocchis.. anyway..

There’s a floating piston inside the air spring that you’re supposed to put more pressure on one side than the other. It’s tied in place with string. This piston runs up and down a shaft, so it has a hole in the middle obvs. There’s an o-ring on the outside of the shaft and on the hole in the middle.

Now – I asked Windwave for a replacement and they gave me a part number. The o-ring that came was the perfect internal and external diameter, but the problem is that the groove it sits in, on the inside of the hole in the middle of the piston, is too tall. Almost (but not quite, and I did try) as if it’s made for two of them. So the o-ring moves up and down in its seat.

If I pack it with oil resistant grease it holds air for a ride or two but ultimately just leaks like a seive. If I fit a thicker o-ring it’s too big to fit the shaft.

Surely this isn’t right? I can’t see how any o-ring would fit though, so I can’t imagine what’s meant to go in there. I certainly only took one round o-ring out (I wish I still knew where it was as I was only changing them as a precaution.. d’oh) and I remember it being a bit bigger than the new one, but it couldn’t really have fit. Unless all I really need is a *slightly* thicker one, that’d still be loose in the groove but provide enough pressure.

Confused.

I have Aldi metric and imperial o ring set. Email me the o ring on top of a ruler and I will send you a selection of O-rings around that size you can try.
Both sets are cheap as chips and Nitrile rings. I can spare a few 🙂

If you can measure the ring and know the internal diameter – even better.

They are all quite “thick”

Email in profile, happy to help. But remember my forum name “Wally” for a reason – I like a bodge. Windwave would be a better bet.

You could look at the Parker handbook

http://www.parker.com/literature/Praedifa/Catalogs/Catalog_O-Ring-Handbook_ODE5705-EN.pdf

Tho ring groove is normally wider than the ring as when you squeeze it in place it needs some expansion room. There is a desired amount of gland fill. I think it is around 80% in the compressed state.

NO.

Talk to Windwave again.

Tho ring groove is normally wider than the ring as when you squeeze it in place it needs some expansion room. There is a desired amount of gland fill. I think it is around 80% in the compressed state.

It’s almost twice the thickness of the o-ring though. Much more than the rest of the o-rings in the fork.

Maybe a slightly thicker one then – not the much thicker ones I bought to try. I have a Screwfix assorted set too, but nothing in there fits at all.

Just a thought – by any chance is it supposed to have a back-up ring in there? (a bit of plastic to support the o-ring). You’d normally only use one in a very high pressure application to prevent extrusion damage but from your description of the groove it does sound too ‘long’. The back-up ring would basically fill up some of the spare space.

Hmm.. It’s possible. Don’t remember anything coming out tho.

To be honest I would also have expected Windwave to have mentioned the back-up ring if there was supposed to be one (you would normally supply the o ring and back-up as a ‘kit’).
Might be worth asking just in case though.

Seeing as you’ve tried Windwave, have you thought of trying TFTuned? They’re a helpful bunch, I bet they’d supply an o-ring and offer some advice.

Have you tried googling for an exploded diagram, just to make sure you have all the correct parts?
I’d was gonna look, but you haven’t specified which fork…

…something like this, it’d be a good place to start, the accompanying parts list would tell you what you need too.

http://www.mountainbikes.net/mtbikes/marzocchisk44rc3titanium150mm2011_b.png

sorry, should have proof read that before I submitted….

Wrong book.. you want parker 5700..
http://www.parker.com/literature/O-Ring%20Division%20Literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

right so for a 100 series o-ring you would have a nominal thickness of around .103″ and a groove width of .140-.145″ with no back up ring, .171-.176″ with one ring and .238-.243″ with two rings.

If you go to page 89 you can see the different gland width and depth for each series of o-rings. this will give to a general idea of if you are in the right ballpark.

ultimately I guess you will need to call someone who actually knows what is supposed to be in there before you try something that seals and hydraulically locks your forks or puts something in a loading condition it wasn’t designed for.

D’oh.

Shop sent me the wrong size. Funny how a 20p part can cause so much trouble 🙂

Are these the same ones you were playing with last year Moley?
If they are I’d seriously suggest you cut your losses and get a new set (sorry)

Although if you mail me over seal specs. I can have go through the boxes and look you out a selection ( as it’s you 😉 )

Yes, the same ones. Problem is there’s no way I can afford a new set, IF I could find something suitable in that size.

O-rings are only 20p so I think it’s an economical repair 🙂 ordered some off ebay. Cost me a lot of time so far but cost not much different to a full service.

What would I replace them with? 160-170mm travel, straight 1 1/8″steerer, big stanchions, cheap…

In a slight thread Hijack are the toolstation oring mulitpacks suitable for fork use? I’ve a set of forks with blown damping I fancy trying to repair which aren’t worth sending off for service.

I’ve found any o-ring you could ever possibly want on ebay, usually about £2 for 10 with free postage.

Just found Marzocchi 55 RC3 EVO titanium on CRC for £340… Mrs Grips suggested I get them anyway.. dammit… Are we still going to be able to get Marzocchi spares in future I wonder?

Look on winstanleys for even cheaper.

Or buy a 350cr from CRC for about the same and future proof your self a bit (join BC to get 10% off).

Why is a 350 CR future proof?

650b

Hmm.. I’m having to buy a straight steerer fork so seems unlikely to be that future proof eh.

What Marzocchis are they? I’ve got a spreadsheet listing spares for all forks but it’s only 2006.

No worries Matt, it’s all sorted.

I have the part number and exploded diag from Windwave, then I googled the part number to find the size. Then I measured the ones I was sent to discover they were the wrong size, so I ordered new ones by size from ebay.

Now I’m trying to decide if it’s worth replacing them anyway.. some nice looking Marz on CRC.

No problem. I nearly did the same and got some 350s earlier this year but managed to get mine up and running.

Did we decide if Marzocchi are continuing to make forks or not?

Will there still be spares?

Well they have a stand at Interbike right now and I’ve seen quite a few 2016 bikes with their stuff equipped but it all depends on what happens after that.

My 66s are getting on for 10yrs old so I might stock up on seal kits.

Fortunately the 35mm seals and bushes were used for ages across the range so they are widely available. Just be glad you don’t have a PAR piston with the bit of string inside. I had to replace mine when the string is no longer available. Tried a variety of different materials, ended up manufacturing one from archer’s bow string, without knots either.