Cannondale carbon steerer with SI bung/star nut

Hi

I recently picked up a Cannondale f&f with a full carbon si fork. It came with the pre installed Cannondale star nut and top cap that acts like a compression bung.

Upon delivery I removed the top cap and noticed a small crack at the top of the steerer. (Speaking to seller about reimbursement). The steerer has been chopped so there is only room for a low stack headset and 5mm spacer

I was originally planning to put the 5mm spacer on top of the stem, this would probably cover the area of the crack so the stem clamped below the damage . However Cannondale don't recommend placing a spacer above the stem as the top cap insert is 40mm long and clamping the stem lower than the insert could damage the steerer.

So I have two options - clamp the stem at the top of the steerer over the crack, though it will have the top cap insert inside steerer to stop it being crushed (as Cannondale recommend) . Or drill out the star nut and use a long bung that will allow me to place clamp the stem lower and use 5mm spacer above them stem .

Neither ideal but is either likely to prolong the life of the steerer? I'd like to try and keep the fork if I can and just check it on a regular basis. I realise this is a risky proposition but I'm hoping the fork isnt a write off ...

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I'd go with the second option (well actually, I'd get some new forks), but you shouldn't need to drill out the star nut. With the appropriate tool push the star nut it down further into the steerer and install a long expanding bung. The problem I see with this option is that when you tighten the bung, it could force the open and enlarge the existing crack.

Here is an image with headset and 5mm spacer installed

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Cheers , the expanding bung forcing it outward is my worry too , at least with the internal top cap sleeve inside and stem outside it has no where to go...

Are there any glues that might be worth applying to the crack to stop it spreading? Epoxy etc ?

Is pushing a star nut down a carbon steerer safe ? I thought that's why they are not generally used

I have had a similar problem with a 1" carbon steerer fork.

As they are shit to come by I had an aluminium sleeve insert machined which I epoxied inside of the tube. It actually goes down past the stem bottoming out a couple mm below the upper headset cup.

an aluminium sleeve insert

I've got a Cervelo P3C in at the moment and that's how they do it: bonded sleeve with a star nut.

Is this a six13 frame? Or at least a frame with the integrated headset? Can you...

1. Get the 'tester zero stack headset cover, assuming you will need more steerer
   
2. chop off the cracked bit of steerer
   
3. remove the star nut carefully. Do not hammer it down. use a small saw to carefully chop off it's arms, or drill it.
   
4. Get the cannondale headset bung and top cap and use that, as the instructions show.
   
5. If you are still short on steerer, use something like an X2
   

Also, instead of an expanding bung, you can glue in one as sold by @mdcc_tester

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What they all said

Thanks the zero stack headset cover could work . Its a CAAD7, I'm using a cane creek 40 which has a 9mm top cap. I think this would be compatible. It would drop my stem down possibly too low though, so may need a more positive rise stem

Have seen posts on the internet where people have glued in stepped extensions to steerer tubes in carbon and aluminium steerers, not sure how safe or reliable this is. Could a customer expander bung with a tall top lip the same diameter of the steerer work as an extension ? Was thinking I could make something like this below and attach it via the star nut, then use a standard top cap

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chop off the cracked bit of steerer

To my eyes, there's at least 12mm needs to come off to get clear of the damaged area. That might still leave enough for a stem if you use no spacers and a low stack headset cover , and you might get your fit back by changing the stem to something with a different angle.

The fact that Cannondale don't trust their own forks without a massive reinforcing block would be reason enough for me to avoid using them altogether. I can get bonded-in plugs made, either light ones for proper forks or heavy ones for Cannondales, but they are expensive as they have to be made individually to fit each fork.

They trust their forks. Team bikes regularly use different systems.

They don't trust everyday mechanics and end users. Fair enough.

@zootsuit the easton EC90 SLX is fair replacement if you need a new fork.

yeah I'm leaning towards a new fork, unexpected expense but I've been reading too many fork failure threads over the last few days !

I've had something similar happen on two Meridas that I have owned. I've had the fork repaired by Mike at Fibre HQ. Not 100% on how he does it but he strips back the damaged carbon and replaces the top section with machined aluminum. I've been riding mine for over 2 years and was £60 to repair.

I've got another fork coming back in the next couple of days so will try and post some pictures of the repair.

Thanks , would be interested to see it .