expander bung

[Brucey]

the way these bungs usually work is that the hollow bolt clamps the top piece to a wedge underneath. There would be little or no point to having the top piece there if it didn't do that, and when it does that, it can't come out separately from the bolt.

These things come in two main flavours; short and long. This is a long one



- the drilling scheme I proposed earlier would work easiest with a shorter one than this, simply because the drill will reach to the wedge more easily, and once the spokes are through the holes they will work better to stop the wedge from turning (if indeed that is the cause of the trouble; it might not be).

cheers

[andrewjoseph]

but that's not what the OP has shown.

you can clearly see the bung is underneath the cap. there is a circle of the same diameter as the outer edge of the allen key socket and it is above the the bung.

Now it may have been assembled incorrectly, but it think it either needs to be pushed up from below (if possible), or some type of slide hammer used to pull it out.

drilling has to be the last resort.

bung.jpg (78.98 KiB) Viewed 755 times

edit:

Brucey, if it is a similar device to you image, then the 'cap' should indeed come off quite easily. then perhaps no drilling will be necessary, just maybe a small screwdriver or some such to try and hold one part of the assembly in place.

[Brucey]

the OP's top part will have a counterbore in it, for the bolt head to go into. I've seen dozens of different ones of this sort and they are all built much the same way.

If you think it is built differently to this then presumably you have seen one like it before. If so perhaps a photograph of one such would help. What you imagine to be the case appears to be a bung with a useless and pointless top part, and that can just drop into the steerer as you try to install it.

.... Brucey, if it is a similar device to you image, then the 'cap' should indeed come off quite easily. then perhaps no drilling will be necessary, just maybe a small screwdriver or some such to try and hold one part of the assembly in place.

I think you may have misunderstood how these things work somehow; the cap cannot come out (not without the rest of the thing) unless the hollow bolt comes out first. The cap is what the head of the screw bears against. In the OP's case the hollow bolt is presumably either stripped or turning with the wedge and therefore not unscrewing.

I agree drilling is the last resort but sometimes that is necessary. I'd certainly try lifting the hollow bolt using an M6 bolt (this ought to allow the tang on the wedge to re-engage) and a load of other things as well before I drilled.

cheers

[andrewjoseph]

the OP's top part will have a counterbore in it, for the bolt head to go into. I've seen dozens of different ones of this sort and they are all built much the same way.

If you think it is built differently to this then presumably you have seen one like it before. If so perhaps a photograph of one such would help. What you imagine to be the case appears to be a bung with a useless and pointless top part, and that can just drop into the steerer as you try to install it.

.... Brucey, if it is a similar device to you image, then the 'cap' should indeed come off quite easily. then perhaps no drilling will be necessary, just maybe a small screwdriver or some such to try and hold one part of the assembly in place.

I think you may have misunderstood how these things work somehow; the cap cannot come out (not without the rest of the thing) unless the hollow bolt comes out first. The cap is what the head of the screw bears against. In the OP's case the hollow bolt is presumably either stripped or turning with the wedge and therefore not unscrewing.

I agree drilling is the last resort but sometimes that is necessary. I'd certainly try lifting the hollow bolt using an M6 bolt (this ought to allow the tang on the wedge to re-engage) and a load of other things as well before I drilled.

cheers

I have never seen an expander/bung of the type you have above. I'm just looking at the pic the OP has put up. I don't think is the counterbore I'm seeing. I can see a definite circle above the allen key socket. have you tried zooming in on this part of the picture? As far as i can tell, it looks like a head doctor type bung under the cap.

This is what i think i am seeing. As you say above "a bung with a useless and pointless top part".

[Brucey]

The OP's bung unit is the kind that has an M6 thread up the middle of the hollow bolt so that works with a standard A-head top cap.

The Hope design replaces both top cap and bung in one unit. The bung doesn't fall into the steerer during installation because (IIRC) it has an O-ring around it. [BTW These units are not permitted in all carbon steerers because many manufacturers require that you have something longer -and often bonded in position- up the inside of the steerer so that it resists the bending loads from the handlebars. Wrong bung = no warranty.]

You can usually tell the top part of any such complete assembly because it overhangs the steerer; if it doesn't do this it can't hold the stem against the headset for preload purposes. The OP's thing doesn't overhang the steerer OD therefore that part is not the top part of the complete assembly, but it is the top part of the bung unit.

Actually there is one other design variant which is that the hollow bolt and the top part of the bung unit are made as one; it could be that the OP's one is like that. In practice this makes little difference to how you get it out, except that it means that there is often one less way of preventing the wedge piece from rotating.... and the hole drilling method doesn't work either....

cheers

[tim-b]

Hi

Actually there is one other design variant which is that the hollow bolt and the top part of the bung unit are made as one; it could be that the OP's one is like that. In practice this makes little difference to how you get it out, except that it means that there is often one less way of preventing the wedge piece from rotating.... and the hole drilling method doesn't work either....

Please see my post dated 8th

Regards
tim-b

[andrewjoseph]

The OP's bung unit is the kind that has an M6 thread up the middle of the hollow bolt so that works with a standard A-head top cap.

The Hope design replaces both top cap and bung in one unit. The bung doesn't fall into the steerer during installation because (IIRC) it has an O-ring around it. [BTW These units are not permitted in all carbon steerers because many manufacturers require that you have something longer -and often bonded in position- up the inside of the steerer so that it resists the bending loads from the handlebars. Wrong bung = no warranty.]

You can usually tell the top part of any such complete assembly because it overhangs the steerer; if it doesn't do this it can't hold the stem against the headset for preload purposes. The OP's thing doesn't overhang the steerer OD therefore that part is not the top part of the complete assembly, but it is the top part of the bung unit.

Actually there is one other design variant which is that the hollow bolt and the top part of the bung unit are made as one; it could be that the OP's one is like that. In practice this makes little difference to how you get it out, except that it means that there is often one less way of preventing the wedge piece from rotating.... and the hole drilling method doesn't work either....

cheers

I don't know how you can say this Brucey. the image i posted has a top cap in it. I've used Hope head doctors exclusively for the last 10 years or so. it has a a threaded section under the 6mm allen key socket.

If i understand you correctly. the bung of the type you have posted an image of, has a threaded section from the very top, and no allen key socket. it has no need of an allen key socket as the long bolt is all that is needed to cause it to expand. BTW, I understand how the unit is supposed to work. if it is the type you say, why is there an allen key socket in there? It's not needed.

The hope type needs an allen key to expand the bung and keep it in place, through which a the top cap bolt travels into the threaded portion for pre-load.

I also know they are not always recommended, but the unit the OP has posted does not fit into any camp. it looks like a bodge of the hope type expander and the top cap of the wedge expander style.

[Brucey]

I don't know how you can say this Brucey. the image i posted has a top cap in it. I've used Hope head doctors exclusively for the last 10 years or so.

I think we are talking at crossed purposes are we not? What I'm saying is that the Hope one comes with its own top cap and special bolt, but most other bungs don't.

If i understand you correctly. the bung of the type you have posted an image of, has a threaded section from the very top, and no allen key socket. it has no need of an allen key socket as the long bolt is all that is needed to cause it to expand. BTW, I understand how the unit is supposed to work. if it is the type you say, why is there an allen key socket in there? It's not needed.

I don't think you quite understand how these bungs work. They are secured in the steerer via hollow bolt typically with an 8mm hex key socket in it. The bolt can be either separate from the upper part of the bung (as per the one I posted a picture of), or integral to it (which might be what the OP's is).

Once the bung is fitted to the steerer, an M6 bolt and standard top cap are fitted. The M6 bolt engages with threads inside the larger hollow bolt. The M6 bolt does not affect how tightly the bung is wedged into the steerer.

I also know they are not always recommended, but the unit the OP has posted does not fit into any camp. it looks like a bodge of the hope type expander and the top cap of the wedge expander style.

AFAICT it is a variant of the standard type, possibly with the hollow bolt integral to the upper part of the bung. If it helps I can post photos of this style of bung, I've got a few of them kicking around here and it might help you to see how they work.

cheers

[andrewjoseph]

I think we are talking at crossed purposes are we not? What I'm saying is that the Hope one comes with its own top cap and special bolt, but most other bungs don't.

I see. my apologies.

I don't think you quite understand how these bungs work. They are secured in the steerer via hollow bolt typically with an 8mm hex key socket in it. The bolt can be either separate from the upper part of the bung (as per the one I posted a picture of), or integral to it (which might be what the OP's is).

Once the bung is fitted to the steerer, an M6 bolt and standard top cap are fitted. The M6 bolt engages with threads inside the larger hollow bolt. The M6 bolt does not affect how tightly the bung is wedged into the steerer.


AFAICT it is a variant of the standard type, possibly with the hollow bolt integral to the upper part of the bung. If it helps I can post photos of this style of bung, I've got a few of them kicking around here and it might help you to see how they work.

cheers

Yes, i am struggling to see the point of the hex socket in the section above the threaded part. If the hex socket isn't needed then it's just taking material away from where it's needed.

[Brucey]

Yes, i am struggling to see the point of the hex socket in the section above the threaded part. If the hex socket isn't needed then it's just taking material away from where it's needed.

the 8mm hex is what you swing on to tighten the bung in the steerer. The stem can slide over the bung , then a spacer (if needed) and a standard top cap are fitted using an M6 bolt. NB the M6 bolt tension does not contribute to the retention of the bung in the steerer in any way; only the 8mm hex headed part does that, because it is attached to the wedge underneath.

BTW on bungs of this type quite often the wedge doesn't have a tang on it, so that the hollow bolt and the wedge can spin together instead of unscrewing from one another. I have several bungs of this type in the spares box and that is part of the reason why they are there; once fitted they can be right so-and-sos to remove. If I ever use them I shall add tangs to the wedge so that it can't spin so easily.

My suspicion is that the hollow bolt and the wedge are spinning together (as described above) in the OP's bung.

cheers

[andrewjoseph]

Yes, i am struggling to see the point of the hex socket in the section above the threaded part. If the hex socket isn't needed then it's just taking material away from where it's needed.

the 8mm hex is what you swing on to tighten the bung in the steerer. The stem can slide over the bung , then a spacer (if needed) and a standard top cap are fitted using an M6 bolt. NB the M6 bolt tension does not contribute to the retention of the bung in the steerer in any way; only the 8mm hex headed part does that, because it is attached to the wedge underneath.

BTW on bungs of this type quite often the wedge doesn't have a tang on it, so that the hollow bolt and the wedge can spin together instead of unscrewing from one another. I have several bungs of this type in the spares box and that is part of the reason why they are there; once fitted they can be right so-and-sos to remove. If I ever use them I shall add tangs to the wedge so that it can't spin so easily.

My suspicion is that the hollow bolt and the wedge are spinning together (as described above) in the OP's bung.

cheers

So pretty much like the hope bung but with a wedge expander.

Where does the inverted conical section of the OP image fit in this?

[andrewjoseph]

Do you think the OP has too much info now?

[Brucey]

Where does the inverted conical section of the OP image fit in this?

it is just the uppermost part of the bung; possibly integral to the hollow bolt.

cheers

[ehelifecycle]

thanks for all the replies I have now sold the forks bung left in