Are my bottom bracket threads worn?

hmmm this bottom bracket keeps coming loose...
hmmm this bottom bracket keeps coming loose…

There can’t be anything worse than building up your classic steel frame after having a respray and chrome plating, only to find that when you install that NOS bottom bracket that cost you a fortune, it’s loose! The most frustrating part of this, is that with a little bit of forethought it could have been remedied before the frame was painted.

Of course once the frame is painted it becomes a difficult issue to solve, and will usually require another respray. Not a happy situation!

Why does this happen in the first place?

In the days before the first sealed bottom bracket units, all bikes had the cup and cone variety. Unfortunately they are not particularly well sealed so the bearings soon suffer from water ingress. Once the bearings become a little worn play develops and if the bike is ridden with play in the bottom bracket over a period of time the threads in the bottom bracket get worn.

Any bike shop that’s been around as long as us will be very familiar with sorting this problem out. However to do it properly will require a respray.

Does my frame have worn bottom bracket threads?

Now if you’ve just bought a frame secondhand and haven’t checked this out then it makes sense to check that you don’t have this very common problem before you have the frame re-finished.