Hello,

My son has a new to him second hand bike. Everything seemed fine for the first week be had it, but now the fork (Suntour XCR LO Air 24″) rapidly loses air. I’ve read that a first thing to try is changing the oil. My local bike shop doesn’t stock shock oil apparently, and I’d prefer to avoid import charges and fees from buying it from Suntour in the States. Does this look like it might work? https://wheelspinmodels.co.uk/i/334725/?gclid=Cj0KCQjwyN-DBhCDARIsAFOELTnJwBUkU7g6DDNIUuoKSOQO2aDtjlR-kqdFfSFof1ct-66-elv0rBoaAjraEALw_wcB. It’s “Traxxas Silicone Shock Oil (80 wt, 1,000 cSt, 60cc)” – shock oil for a remote control car. The Suntour oil is “80w”.

Cheers,

Sacha

I’m not familiar with that fork, but if I was trying to fix an air leak, I’d think seals and air valve before an oil change.
Have you put soapy water over the valve core to check for leaks? Or maybe even put the whole fork in a bath of water.

I’d check the valve first before taking them apart.
Also look at the air side stanchion for any deep gouges – will loose air when it passed the seals.
Other than that it will be new seals.
You can speak to these guys and possibly get a service kit:

https://www.greyville.com/

They’re the UK importer of Suntour.

Have had big issues with suntour/greyville I would not bother with the fork. However if you do want to repair it is a simple fork.

There is not oil bath or the like in the forks and it is all just grease. TFT will have suitable grease.

Suntour recommend the 80wt oil to beef up the air piston seal to remedy the air loss problem. It’s not a weight typically needed in bike forks as it’s so thick, so bike shops are unlikely to stock it.

Not sure if this is any help.
I replaced the grease in the lowers of my Raidons with some generic oil and some wiper seals in the top (had to trim down the nearest fit I could find). Made the world of difference to the smoothness.
But, might not help with an air leak issue.

As others have said, best thing to do is to remove the fork from the bike, pressurise and submerge to see if the leak is coming from the air valve (a very easy fix) or if it’s coming from seals somewhere. If the latter, realistically the fork needs a strip down and seals replaced. If there’s a score or crack in the air chamber then that’s basically landfill. Gumming it up with grease is only a partial solution, air pressure will still force the grease out of wherever is leaking air.

had a similar air leak on my lads bike that we bought S/H too. Turned out to be the air top cap leaking against the fork body, a few winds of pfte and all sorted.

Thanks all for the brill advice! I will do some examining and testing. I have lost confidence in these forks now. I will try to fix them, but think it’s quite likely I will come back to you good folks for some more advice. Probably about what to replace them with!

https://www.youtube.com/watch?v=f6W5Zwv4t
I’ve followed this to fix a similar problem with Raidons. Worked a treat. You may need to visit a bike shop to get top cap off and then refit it as it needs a thin profile socket

Hi Stewmur,

Thanks very much for the link. Unfortunately for me, when I clicked it to watch it just now Youtube told me that the video was unavailable. 🙁

I’m glad to hear you fixed your Raidon issue though 🙂 Congrats! I’ve never serviced a fork before, and am a bit nervous about it.

Hello folks,

My diagnosis attempt are paused just a for a while probably. *We’d had the bike turned upside down* for about 5 days in the garage – as we’d heard that it can sometimes make the oil trickle back down over the innards and stop the air leaks. Then after reading your diagnosis tips we turned the bike right side up and gave it a test pump up to 100psi and a ride up and down the road, and it held it’s air in!

This seems too good to be true. I anticipate restarting the diagnosis soon.

In the mean time, I’ve discovered the forks on *my* bike are misbehaving. Bah! The are cheap RS coil ones though, and I’m feeling a bit braver since your advice. Off to do some googling. Thanks every one again!

Funnily enough, we have exactly the same problem with exactly the same fork. I serviced it a while back which seemed to help. Then it started leaking again so I smothered the air cap in silicon grease, which seemed to work. Until it didn’t.

I’ve swapped them out for some carbon rigids now, but I will try the valve trick for one, and the upside down trick for two. I couldn’t find an in-stock service kit either – nearly just bought a new fork from Aliexpress!

Hi Rich S,

It’s good to hear that you’ve been able to get the forks going again, even if temporarily. Have you found any nice instructions for servicing them?

I think I’m about to get some old Mazorcchi air forks on ebay – though slightly in pieces and 26″ and see if I can get them going again. According to the vendor all they need is some new o-rings and oil.

Oops, sorry. Try this one:

https://www.srsuntour.com/service/tech-videos/

Right hand column, 5th one down

@badcycling He seems happy on his rigids so I’ve not bothered with the Suntours. I’ve previously done stewmur’s link servicing but it hasn’t worked long term. I’ll find some time and make sure the valve isn’t leaking, then plan B and plan C…

Finally got around to pumping the forks up and putting them underwater… they are pissing air out of the upper post mount brake hole!
Lord alone knows what I’ve done wrong. When we got them they would lose air. So I serviced them, then this.
I guess I’ll be rebuilding them again. Unless anyone has any insight?

lowers shouldnt have any significant pressure if they arent compressed so leaking from the air spring into the lowers.

Have you tried the 80wt oil on the air piston o-ring? @stewmur posted a link to the video how-to.

Yep, it’s got the 80wt oil in.

Funnily enough, under 150psi it doesn’t seem to leak. Then I let the pressure down to 50ish, cycle the forks, and they leak. And don’t really stop. So it’s the air spring onto the bottom seal. Hmmm.

I’ll pull them apart and redo everything tomorrow.

Have you tried removing the o-rings, and replace if possible. Stick a little grease on before remounting the o-ring can help. Alternatively I have a good as new pair of 24″ coil Suntour’s that I removed and replaced with air forks on my sone bike..