I'm having problems with the bottom bracket on my Thanet Silverlight. It has an unthreaded bb shell with a TDC bb insert which is prevented from turning in the shell by a brass bb oiler. The bb oiler screws into the shell and into a slot in the TDC insert.

From when I got the bike the bb lock ring would loosen after just a few miles so I Locktite'd it. That worked for a while but despite the lock ring being fixed the assembly started loosening again. I took it apart yesterday and found the end of the bb oiler had sheared off. The bike has a Sturmey Archer fixed-gear ASC hub and it's obvious the brass bb oiler is just not up to the stress of preventing the TDC insert from rotating in the bb shell with fixed gear.

I think the solution might be to replace the bb oiler with a blanking screw of some kind, made of a stronger material, perhaps stainless steel, but I can't find any info about the bb oiler's thread size. Does anyone know?

Also, I'd like to replace the present cottered crank with a cotterless Stronglight 49A/TA set that I have. Does anyone have experience of performing such a change on a machine with a BB shell? For example, will a TA or Stronglight axle work with TDC bearing cups?

The BB assembled


The BB Shell


The Insert


The Inadequate BB Oiler/Insert Lock

That looks less like an oiler than a zerk fitting for grease. I have a 60s Falcon frame that came with one of those, brass, and it had a spring-loaded bearing closure. The top of it was bunged up, but the bottom was in good shape. Like many "plumbing" items, this had a tapered thread. I removed it, and tapped the hole for a metric 5 mm x 0.8 screw, which I plan to use as an oiler (thumb turn in and out). The BB shell is not all that thick, and yours even less so. If it were mine, I'd be tempted to use both holes in the top of the shell, and drill/tap holes into the insert and the shell.

Charles,

Many thanks for the very, very helpful reply. I'd just assumed i was limited to the size hole already there. And the idea of drilling my own holes in the insert really makes a lot of sense - a really neat idea. Thanks again!

I think Charles is on the right track as it seems that a single contact point to stop that shell from rotating is a pretty poor design. And it probably wasn't intended to be used with a fixed-gear hub, putting that much more stress on that puny oiler/stop.

Neal

That's a good point. I was told by the seller that this machine had originally had an ASC hub but it wouldn't be the first time he has proved to be, er, economic with the truth. All I know for sure is that it has a brazed on mount for a Sturmey Archer cable wheel. Certainly, the size of the hole in the insert, being almost twice the size of the stop, will invite rotational play.

I wonder now if I should forget the ASC and use an FM instead, or modify the shell as Charles suggests and stay with the ASC...