Rear Mech Cable Clamp Bolt Problem

cleeve hill reject

Hi guys, I was fitting a new cable to my Dura Ace 7700 rear mech when I noticed that the cable clamp bolt wasn't tightening. I then noticed that a coiled bit of wire had come out of the top of where the bolt screws in to. This coiled wire is pitched at the same spacing as the thread on the clamp bolt. Now the hole to screw the bolt into is too bid a diameter so I'm assuming that the coiled wire was inside the hole and the bolt screwed into it? Seems a bit of a strange system to me, has anybody had any experience with this? I need to get the mech sorted out as soon as possible!

cleeve hill reject

Just done some research and it seems that the 'spring' is a helicoil, a twisted wire that is screwed into a large diameter hole and acts as a thread to reduce the diameter of bolt required. Seems a special kit is needed to get a helicoil into the hole so it seems like I will need to try and find a larger diameter bolt that I can fit into the threaded hole that I am now left with. Irritating system that seems to be completely surplus to requirements!

square_wheels

It is indeed a helicoil, sometimes called a recoil or thread repair. They're used for either thread repair when the original is damaged/stripped or, most likely in this case, used to provide a stronger thread for the bolt to fit in - normally where the metal being threaded is soft (e.g. Aluminium, Brass etc). We use them quite a lot at work for repairs in alloy components. They have their own thread pitch (the distance from the top of one thread to the next) and diameters to ensure the resulting thread inside is the correct size for the screw going in to them. They're quite easy to fit, worth googling them, I'm sure there are how to guide out there somewhere.

You might find you can get another bolt to fit the hole left behind, but it will probably cause more damage in the long run and not fit properly. These thread repairs (helicoil or recoil) are available from most fixing suppliers, bearing companies and engineering suppliers. You might find a freinedly local engineering company who could help as well, it's probably worth phoning one or two to see.