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I just cut the steerer on one of my road bikes. The steerer is long enough with stem slammed, there is a few mm steerer above the stem so I can place a 5 mm spacer above which I believe is good practice
Issue is when I go to fit the bung it only goes in 3 cm. So I had a look down the steerer tube and there are loads of carbon offcuts and stuff in there, which clearly shouldn’t be there, and is stopping the bung going further down the tube. My mate has the same frame, has slammed the stem, and it fits a 6cm bung no issues so there is clearly an issue it if my making
given the bike is second hand and 7 years old, I can’t see boardman helping out, even though it’s clearly a manufacturing error. I’m reluctant to dremel out all the carbon bits inside the steerer.
im wondering if running a hope head doctor would be safe. I thought common wisdom was the bung should extend past the base of the stem. The stem is 4cm long,
thoughts?
IMHO the best place for a fork bung is within the upper and lower limits of the stem.
@scotsroutes?
to clarify do you mean you don’t think it should extend past the bottom of the stem? Ie if I can find a 3cm long bung I’ll be grand?
that’s not what I had thought, but tbh I’ll be delighted to be told otherwise! I can’t imagine a bung would provide much additional strength to the clamping area tbh. I only do the stem up about 3.5 nm on a carbon steerer anyway. So thought there may be some other rational
no idea where I’ll get a 3cm bung from though! Im pretty sure a head doctor doesn’t fit in a carbon steerer tube, only alloy ones
do you mean you don’t think it should extend past the bottom of the stem?
Yep - that's what I mean and how I fit mine.
Interesting! I assume you have been riding carbon forks like that for years? I’ve found the following bung that would fit but wouldn’t be long enough support the bottom stem pinch bolt but if you are right this is the solution
ive emailed boardman bikes but given they are now staffed by halfords I’d say the response will be next to useless.
Regardless, still think a shorter bung is safer than taking a dremel to the inside of the fork however!!
Hope Head Doctor is designed for alloy steerer forks - the one time I tried to use one on a carbon fork it was too big. Steerer bung’s main job is to support the open end of the tube and stop it being crushed/split - good if it extends below the stem, but not essential IMO. Carbon shards down the steerer may mean that someone’s tried to fit a star-dangled nut, or rammed a bung in there already - smoothing it out with a dremel or emery paper wrapped around a dowel probably won’t do in any harm, carbon fork steerers are hugely overbuilt anyway.
carbon fork steerers are hugely overbuilt anyway
If they were they wouldn't need bungs to prop them up.
Load of shards inside a carbon steerer? 100% would not ride. If there's signs someone has rammed a star nut in there then removed it just bin the forks before they cause a serious crash.
Its 100% not been caused by a star nut. It’s clearly a manufacturing defect. If I could work out how to post a pic I have one which shows the issue. Basically the steerer tube has a big bit of carbon dissecting the middle of the inside of the tube. If it’s meant to be like that it would make it impossible to slam the stem and still fit a bung longer than 3cm. It doesn’t look to be there on purpose however, it looks very very rough.
it’s a tt bike btw, so slamming the stem is hardly a surprising thing for an owner to be doing!
more I look at it the more I question the integrity of the fork. It’s clearly not been manufactured correctly. I initially thought it was part of the fork bladder that had been left in, but it’s clearly carbon
Here is the inside of the fork
https://www.flickr.com/photos/193301801@N05/53224884932/in/dateposted-public/
that doesn’t look right at all
Based on that picture I would be seeking a replacement fork. Admittedly it's really hard to tell what's going on from the picture but I'd err on the side of caution, something doesn't quite feel right. Im not convinced it's a manufacturing issue.
Whilst I’d agree about having concerns about the integrity of the fork, Why do you not think it’s a manufacturing issue? The carbon in there is rock solid, it’s not delaminated from the inside of the fork although I appreciate you can’t tell that from the pic
What I think has happened is they have reemed out the centre of the steerer tube of all the crap, but not done it far enough down. I showed it to the guy at halfords who now own boardman and he was actually really helpful. He seemed to agree it was a manufacturing defect as described above, and told me the customer services helpline would be useless. However he has taken some pics and is contacting some folks in boardman to see what they think, including if they can take the fork back and remove all the crap inside if possible. I may also contact carbon repair to see if there is anything they can do to clean it out and check it’s structurally sound
I wouldn't want to go anywhere near a carbon steerer with a reamer.. Is it a cross-braced section steerer, like two D sections back to back, but someone has damaged the upper part?
Is the raggedy cross-brace you can see across the top of the crown (ie where the steerer tube attached to the crown ?
As there seems to be a step in the tube , making me thing that is where the steerer tube is attached (bonded) to the crown.
It does look a bit shiiite. I'd want to understand the construction of the fork and more photos etc before being at all confident to proclaim anything
i have no idea what a cross based section steerer is! The carbon bit down the middle does look very much like it’s fairly central, however it’s not a perfectly straight line dissecting the inside of the fork. A check with an endoscope doesn’t show any delamimatiom from the lower walls either
The other point is that my mate has the same frame and this isn’t in his fork. His steerer is cut shorter than min yet can get a 6cm bung in there. So I’m 99% certain this is a bit of carbon that’s has been left in there in error or shouldnt have been there in first place
one further point of disclosure. I’m actually rebuilding this bike up to sell it as it’s no longer required. I actually have another fork which would probably work fine with it however it’ll be far harder to sell without the matching fork
obviously if I was a total dick I could just stick a shorter bung in there and anyone buying it would be none the wiser, I’d probably happily ride it with one in (scotsroutes has been doing that for years). Or I could take a dremel to it and have it fixed in 5 min. But I’m not going to sell it on a bike until someone that knows what they are talking about (either boardman or a carbon specialist) tell me it’s safe to do so
carbon fork steerers are hugely overbuilt anyway
If they were they wouldn’t need bungs to prop them up.
Quite a lot of them don't. I've got a dozen or more on bikes and only about half actually *require* a bung that supports. The rest have really thick walls.
Is it a cross-braced section steerer, like two D sections back to back, but someone has damaged the upper part?
I had a kinesis (i think) built fork with one of those, about 8-10cm up from the bottom of the steerer. I can imagine someone wedging a too long bung down there would have damaged the top of it.
So I’m 99% certain this is a bit of carbon that’s has been left in there in error or shouldnt have been there in first place
Maybe, but thinking about how a carbon steerer is normally made I don't understand how it would happen. There's probably a simple explanation though.
Jameso is explaining my point better than me. It somehow doesn't make sense/look right.
I agree it doesn’t look right for sure!
the carbon bit is really thin, you could almost cut it with scissors so it looks like a layer of carbon that hasn’t been bonded correctly or something . And as I say it’s not in my mates same fork. I’ll see what boardman says
the bike is years old and i assume has done many miles so I think it’s structurally sound. Or at least it was until I cut the top off it and now can’t fit a proper bung.. what a clown I am!!😢
Quick update (prompted by a couple of other threads on the dangers of carbon) !!
so it turns out that the crap inside the frame is how it’s meant to be. I checked my mates boardman road bike fork and it’s identical
so with knowledge that there is nowt wrong with the fork integrity, I had to address the issue of not being able to fit a 4 cm bung in the steerer. A couple of bike shops told me it was fine to use a shorter one, and it actually transpired that the bung in my giant defy carbon fork, set up in the factory, was only 3 cm. So confident it wasn’t an issue, I used that
still an absolutely stupid design building a tt bike that you can’t slam the stem without scouring the planet for an odd length bung, but hey ho.