Carbon repair

[Dr.Robotnik]

So for many moons I have been trying to restore my Sunn and the biggest sticking point and the one that has down hearted me the most is the forks as shown below.

They are an air oil fork and have carbon tubes for legs. So far in the many years I have had them, I have replaced the seals and have had them serviced three times. They've never worked properly even back in the day, I now have one issue stopping me riding them.

The problem now is the left carbon leg has a minute crack (less than 1 cm long), which weeps tiny droplets of oil and obviously doesn't hold air, thus the fork is useless.

I have spoken to carbonology about a repair and they say it won't stick because there has been air and oil in the fork. I have them with justbackdated now and was wondering if anyone could help as the fork is pretty rare.

So what can I do?

Can I only fix them by replacing the whole tube? How can I replace the whole tube? Anyone know where I can get a tapered tube like this?

Any ideas?

 

[velomaniac]

Unless its a typo you say they never worked even BITD and thus why do you persevere.

Get a different fork

 

[Dr.Robotnik]

Unless its a typo you say they never worked even BITD and thus why do you persevere.

Get a different fork

Wow, I don't know what to say... :cry: edited my original post for clarity :roll:

I would like to get them working. Fixing the tiny crack is all that is stopping me.

Please can you help? Can anyone offer advice?

 

[mattbrown]

can you not cut out, or file away the oil tainted carbon and fix it

 

[marin man]

I think the problem will be that the fork being made up of fibres will be contaminted with oil as it will "soak in the crack to a cetain extent,If you can access the inner side of the fork leg you may be able to use a liner and bond that on to the inside of the leg,or make a carbon wrap up and wrap it and bond it round the crack so it is completely sealed from the outside,the trouble will be if the leak has pressure pushing on it from the inside,as this,in time,will push the repair off,a pic of the damage would make it easier to see where we can help.

 

[Dr.Robotnik]

From what I understand the oil will have soaked all the CFRP and so the material can not be cut away and patched as the repair will eventually delaminate and fail.

Some of the repair places I've spoken to recently won't even allow it into their facilities to repair because it because it has had oil in it and it risks contaminating their products and materials.

Sorry the crack is so small it doesn't show up on camera at least not with my camera/phone.

I have been looking into making my own tubes today and it seems like it is not so hard. I would rather just buy a tube though or have someone else make it as I don't have time.

The problem I for see is removing the existing tube from the alloy lugs and then bonding the new tube back to the alloy.

If anyone has any advice or experience, please let me know.

 

[marin man]

I have done this before and the easiest way is to heat it up,If you want the tube out whole as a pattern,then heat the lug up with a paint stripping gun,if you do not need the tube then you can stick it in the oven on 180 degrees for about 25 mins,and it will come apart real easy.

to reglue it you will need some epoxy type glue for carbon,I have some and if you pm me when you are ready I will stick some in the post for you

 

[Dr.Robotnik]

Wow, thank you for the offer Marin Man that'd be ace. I will give you a shout if needed.

Current idea would be to make a tapered tube and bond it inside the current one making a full internal patch, then expoxy filler the outside crack cosmetically. Just need to somehow make sure the internals are totally clean, no idea how though.

 

[marin man]

First of all then,you will have to degrease the internals with some good quality degreaser then when they are completely dry you will have to clean them with some acetone or nail varnish remover but be sure to use acetone and not the acetone free stuff,then seal the ends and leave to evaporate for a good ten minutes.then glue away but work quickly and then do not move it anymore for at least twenty four hours then your done

 

[Senri]

I do suspect there must be some kind of liner inside already. Maybe that broke first, soaking the carbon and maybe even causing the crack. Any epoxy based material is poreus and it is unlikely that they used plain epoxy for a oil filled pressure chamber.
Horror stories enough on epoxy breaking frames etc, but be seriously carefull contructing your own legs. I certainly don't want to critizise your abilities, but most home kits don't produce products with the strength of industrial products, even though they may look perfect. I don't want to see you hurt because of a failed home made carbon leg.