Sunday, 30 January 2011

Bottom brackets

On Friday morning I noticed that the bottom bracket spindle on my 1978 Viscount Aerospace Pro seemed to be running loose in its bearings.  This caused the chain wheel to wobble and my gear changes to be a bit hit-or-miss.  It also prompts me to talk about the bottom brackets used in Lambert and Viscount bikes.

[Note for people who do not speak ‘bike’:  The bottom bracket is the bit at the bottom (!)  where the pedals go round and round.   The spindle (or bottom bracket spindle) is the bit that is attached to the cranks and the chain wheel.   (It is a spindle, rather than an axle, because it rotates.  Strictly speaking axles don’t turn.)  The bearings are what the spindle turns in.  Traditionally, the bearings were made up of separate bearing ‘cups’ and loose balls.   Together the spindle and bearings make up the ‘bottom bracket’.  The part of the frame in which the bottom bracket fits is the bottom bracket shell.  Nowadays, most bottom brackets are sealed units.]

Lambert was an early adopter of ‘sealed’ bearing units - in fact industry standard ball bearings.  These push fit into the bottom bracket shell and the spindle fits into the bearings.  Circlips were fitted to the spindle to stop any tendency to move from side-to-side.  A similar arrangement was used on Klein bikes.  Here are some photographs and text about changing Klein BBs, which might be of use if anyone is changing a Lambert or Viscount one.

Certain problems arose with the Lambert BBs.  Early spindles and crank sets had parallel-sided square ends, unlike the square tapers then usual for cotterless crank sets.  This was asking for trouble and the cranks were inclined to work loose as the holes in them became enlarged.  Later versions had the normal tapered ends, but there was always a question mark over the accuracy of the machining and the Lambert/Viscount cranks require careful alignment.  Another problem that has been reported is early failure of the spindle, which has been attributed to stress-concentration due to the grooves for the circlips, but might be due to poor castings.  If this happened when you were cycling fast or going uphill it would certainly be frightening, possibly dangerous.  There is a good photograph of Viscount BB spindle failure here and also a way of curing the problem.

Another point is that normal cartridge bearings are not totally ‘sealed’ and they are vulnerable to road dirt getting in and wearing them out.   This is probably what has happened to mine.

Next time I’ll write about the options for your Lambert or Viscount bottom bracket, should you need to replace it, and I hope I will have sorted out mine.

1 comment:

  1. My Aerospace Sport had its BB bearings seize completely about 15 years ago. Couldn't work out why. The LBS (a decent one) eventually found the problem: water thrown up by the rear wheel, hitting the underside of the seat and going down the open end of the seat-post (must have been pretty wet that year!). As we all know, the seat tube and main tube ends protrude into the BB shell, so water gathered inside the BB shell over time and naturally seized the bearings. They were able to thread the BB shell and replace with standard removable BB lock-ring. Then last year I had the BB shell properly overhauled: the tube ends reamed out of the BB shell so that it can take standard BB set. But apart from the top of the seat tube fatiguing and developing a crack, I've had no other structural problems from the bike (and that's included transporting two children on the back!)

    My other Viscount, an Aerospace Victor, has been ridden little in its life and still has the original BBs and spindle intact and working well.

    Great blog! Keep the posts coming please! b :)