replacing the threaded insert on a carbon fork (mudguard fitting)

[da_murphster]

I recently bought a boardman 8.9 adv which was missing the threaded insert for fitting the front mudguard - they discounted the bike heavily because of this.

Its mudguard season so I'm looking to fix this, just rung boardman who do not supply spares for this (they suggested either a new fork or a plastic wallplug!!)

My LBS said they could potentially bond in a stud there - not ideal for me as I think thats a bit fugly!

I assume I could fit a plastic rawlplug - or would that be dodgy (crushing the carbon). I really don't want to cock this up.

Any suggestions how I fix this?

 

[Racing roadkill]

I recently bought a boardman 8.9 adv which was missing the threaded insert for fitting the front mudguard - they discounted the bike heavily because of this.

Its mudguard season so I'm looking to fix this, just rung boardman who do not supply spares for this (they suggested either a new fork or a plastic wallplug!!)

My LBS said they could potentially bond in a stud there - not ideal for me as I think thats a bit fugly!

I assume I could fit a plastic rawlplug - or would that be dodgy (crushing the carbon). I really don't want to cock this up.

Any suggestions how I fix this?

Very careful fitting of a riv nut, may do it. But you really will have to be careful. You’ll need an M5 ( I think ) Riv nut, and a rivet setting tool. Both of these are readily available from Halfords.

https://www.halfords.com/webapp/wcs...goryId=318447&productId=1247801&storeId=10001

 

[Smokin Joe]

Nut and bolt?

 

[si_c]

Hmm, my first thought is to epoxy a smaller nut into the hole and use a couple of rubber washers either side to ensure a good fitting. Even with an imperfect alignment of the nut you should get away with it as it's only a small nut.

My second and possibly better thought would be to use something like sugru to completely fill the hole - pack it full and get it reasonably colour matched - and then drill a hole into the sugru and tap some threads directly into that. The advantage of this is that if it goes wrong you just repack with sugru and try again and there is little to no weight bearing on the threads so even though they are non-metal they should hold, just grease them properly.

The advantage of the second method is that you can use the correct sized thread and bolt for the mudguards.


The disadvantage as far as I can see it is that I don't know about any chemical reactions which might take place between the carbon and epoxy or sugru.

 

[Yellow Saddle]

Show us a photo of the area please. That would help.
I have an extensively modified carbon fork and the mods were done with standard lay-up epoxy. I had no mudguard fitting hole, so one was drilled and a threaded insert glued in place. Also, I have internally-routed the the dynamo wire by drilling an entrance and exit hole and inserting an aluminium tube, which was then glued at both ends.

Carbon is very forgiving and if you understand it and use the right epoxy, you can do extensive and safe mods.

Don't put any expanding plug, rivnut, plastic wall plug, rawl type fitment etc, in there. The fitment must remain passive.

 

[da_murphster]

Thanks for the answers.

I'll get a photo up later.

I'm wondering if expoxying a helicoil in might be the answer? No risk of crushing the carbon etc. I need to have a look as I can't remember if the hole is hollow behind or a 'tube'

 

[Yellow Saddle]

Thanks for the answers.

I'll get a photo up later.

I'm wondering if expoxying a helicoil in might be the answer? No risk of crushing the carbon etc. I need to have a look as I can't remember if the hole is hollow behind or a 'tube'

Not a helicoil, but threaded insert. Something like this:
https://www.ebay.co.uk/itm/THREADED...hash=item5464edca75:m:mudrNBRbi1_dBIdzTVmYvSw

 

[da_murphster]

Nut and bolt?

 

[Smokin Joe]

View attachment 487542

Sorry, I thought you meant the bottom of the fork leg to attach the stay.

 

[Yellow Saddle]

View attachment 487542

Aha, I see the problem. That one's easy. Simply get one of those threaded inserts I mentioned in the link and epoxy it in place. Make a little jig beforehand so that you can hold it nice and true whilst it sets. You can even use a rivnut but not "pop" it. Insert it so that the flange remains outside and build it up behind it with epoxy that can file and machine. Glue it in first then fill and chamfer it nicely with that black superglue filler stuff. I can't think of the name right now, but it is basically cyanoacrlate and bicarb of soda.

 

[Racing roadkill]

Aha, I see the problem. That one's easy. Simply get one of those threaded inserts I mentioned in the link and epoxy it in place. Make a little jig beforehand so that you can hold it nice and true whilst it sets. You can even use a rivnut but not "pop" it. Insert it so that the flange remains outside and build it up behind it with epoxy that can file and machine. Glue it in first then fill and chamfer it nicely with that black superglue filler stuff. I can't think of the name right now, but it is basically cyanoacrlate and bicarb of soda.

Agreed. An epoxy / rivnut combo would work.

 

[CXRAndy]

Epoxy a rivnut in position. The flange face will hold it neatly in place whilst the epoxy cures

 

[da_murphster]

I was originally thinking of a plastic rivnut - mainly as they would be easy on the carbon fibre and have brass inserts so no rust.

I am assuming that any 'normal' rivnut will rust?

I think I will probably buy a selection and see what fits the hole the best.

 

[CXRAndy]

I was originally thinking of a plastic rivnut - mainly as they would be easy on the carbon fibre and have brass inserts so no rust.

I am assuming that any 'normal' rivnut will rust?

I think I will probably buy a selection and see what fits the hole the best.

You can always enlarge hole if rivnut is just a little oversized