Radical fix for a very radical problem

[BaGearA]

**This is an old ALU crown and stanchions that are junk , I am just using them to explain my point.

 

As you can see here there is a hole in the arms of the crown that go to the stanchions (prob to save weight) now that part of the stanchion you can see there is where I suspect the damage is THUS is leaking there -> going through the arm -> into the steerer -> and leaking out the top.

 

IT IS A CARBON CROWN SO THERE IS NO HOLE AT THE BOTTOM

 

 

********** EVERY SINGLE SEAL AND O-RING ON THE FORK IS BRAND NEW SO DON'T TELL ME TO REPLACE SEAL WHEN AIR IS LEAKING OUT OF THE TOP CAP

[JXV]

Those top cap threads on the stanchion look very clean as does the surrounding portion of the crown. Airspring top cap Oring should seal against the inside of the stanchion tube, on the exposed smooth portion above the threads in your pic, not against the top of the tube although there might be another seal there.

 

Presume the airspring side is leaking and the fork goes soft after a while....?

 

post a pic of that top cap too.

 

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[BaGearA]

Now logic tells me obviously there is a connection between the damaged part of the stanchion and the crown and thats why I'm going to attempt to seal it some how.

 

 

 

any more suggestions welcome:) 

[JXV]

possibility of a crack in the alu stanchion tube?.....in which case there is no alternative but a new stanchion tube if it can be fitted.

 

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[BaGearA]

Those top cap threads on the stanchion look very clean as does the surrounding portion of the crown. Airspring top cap Oring should seal against the inside of the stanchion tube, on the exposed smooth portion above the threads in your pic, not against the top of the tube although there might be another seal there.

 

Presume the airspring side is leaking and the fork goes soft after a while....?

 

post a pic of that top cap too.

 

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jip

[BaGearA]

possibility of a crack in the alu stanchion tube?.....in which case there is no alternative but a new stanchion tube if it can be fitted.

 

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No cracks any where.

 

 

 

There is a machine to press new stanchions but  AFAIK no one in SA has one , I hope to one day have one and then be able to help people with new stanchions instead of having to order a new crown assembly.

 

will post pics of top cap now.

[BaGearA]

The marking on the topcap makes me think someone in-experienced worked on it before me.

 

* O-ring and valve core are brand new.

[BaGearA]

.

[PeterF]

Its a carbon crown so no hole at the bottom

Then it seems like your only option will be to fill up the lower part of the steerer tube with epoxy.  Good luck.

[captain morgan]

I dont think foam is a good idea , too porous.

I think epoxy resin as for carbon repair might work , and maybe try rigging a plunger of some sort to put pressure on the resin to push into the the crack. Something like the plunger in a plastic syringe .

Good luck !

[DJR]

Pity we don't have a medical guy that is willing to look at it from the steerer tube side using his endoscope camera to take pictures and try see if a hole is visible, or at least see where the air bubbles come through.

[DJR]

I dont think foam is a good idea , too porous.

I think epoxy resin as for carbon repair might work , and maybe try rigging a plunger of some sort to put pressure on the resin to push into the the crack. Something like the plunger in a plastic syringe .

Good luck !

Biggest plastic syringe you can find (pharmacy) with a long thin flexible plastic tube (garden irrigation / nursery) attached. Mix epoxy, flow it into syringe, get all air out (difficult but possible). Stick thin tube down the steerer tube, make sure it is all the way down, preferably into the crown, and inject. Then vibrate to make it settle and seal as well as possible. Crazy fix, but if all else fails, why not??

[BaGearA]

Pity we don't have a medical guy that is willing to look at it from the steerer tube side using his endoscope camera to take pictures and try see if a hole is visible, or at least see where the air bubbles come through.

I was actually thinking of trying to get one that works with modern smartphones 

 

 

http://www.ebay.com/itm/New-Android-Endoscope-Waterproof-Borescope-Micro-USB-Inspection-Video-Camera/121997170733?_trksid=p2047675.c100012.m1985&_trkparms=aid%3D777003%26algo%3DDISCL.MBE%26ao%3D1%26asc%3D38530%26meid%3D5d674389962a40d399b4d92a4d8484a7%26pid%3D100012%26rk%3D3%26rkt%3D10%26sd%3D171827746965

 

 

something like that ^

[BaGearA]

Biggest plastic syringe you can find with a long thin flexible plastic tube attached. Stick it down the steerer tube, make sure it is all the way down, preferable into the crown, and inject. Then vibrate to make it settle and seal as well as possible. ?? 

Was also thinking if i could somehow get a metal sleeve over the tube I could guide it down the steerer with a neodymium magnet my cousin has

[JXV]

.

The O ring on that top cap is made to seal against the inside of the fork stanchion above the threads. If it is the correct size, clean and well lubricated with no scratches inside the stanchion tube or the O ring groove, it WILL seal.

 

This means that air is probably NOT exiting into the crown from the top cap joint. The leak is somewhere else and it can only be a hole or crack in the stanchion tube. This brings up the obvious questions of how did it happen and will it be safe if you manage to seal the leak without repairing the structural damage.

 

If you do try an epoxy type repair to seal the leak then the best way to ensure it withstands the pressure is to apply it from the inlet side of the leak rather than patching over the exit point which hardly ever works. However you don't have access to the source side of the leak so use a fairly fluid epoxy and pressurise the steerer tube for a few minutes after adding the epoxy. This will force the liquid epoxy in reverse through the leak path where it will solidify and cannot be displaced by future pressure.

 

Still have my reservations about that stanchion though.

 

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[DJR]

Was also thinking if i could somehow get a metal sleeve over the tube I could guide it down the steerer with a neodymium magnet my cousin has

If you want to make a semi flexible thing slide into all kinds of nooks and crannies, this is what you do (again, not a bike application, but the principle is what counts):

 

Make a bend of about 20 to 30 degrees 3 to 4 cm from the tip. A plastic tube can be heated with a heat gun and then bent. A very flexible rubber tube can be made more rigid by sticking a wire into it and bending it where you want. (Wire can be removed after pipe is in place) Round the pipe tip edges off with a file, sandpaper or by melting it carefully.  Just enough so the outer edges will tend to slide past obstacles and not hang up on little rough places. Then, when you insert the tube, you move that bent tip forward and when you encounter an obstacle, you rotate, pull back a bit, push it down, rotate and so on until it slides past. It is amazing how that simple bend close to the tip will make it go around blockages.