Spudh wrote: I'm wondering what sort of mileage would be considered normal for these to go. I replaced the wheel bearings at the same time and these are all fine.
Viscount boasted back in the day that the bearings would last the life of the bike so 2500km seems worrying!! But seriously, I think 2500km is not great. I would expect at least 3000 miles from a set of BB bearings. When you replaced them previously how did the spindle feel when you turned it by hand (without the cranks on)? It has to feel super smooth with absolutely no binding, roughness, etc. Getting this is easier said than done as everything in the BB has to be a snug fit and dead square. After 30+ years of use is this realistically achievable? At the factory, the spindle was pressed in through the bearings. All we can do in our garages is pull (or hammer!) the spindle through and hope everything lines up to perfection. The factory did not always get it right with the bearings in the BB. I recently removed an Aerospace spindle and bearings from the frame because the spindle felt rough when turned by hand. Examination of the parts showed that the bearings were fine. The spindle was the problem - the machining was, err, adequate at best. Checking its thickness with Vernier calipers showed a fair variation in its thickness along much of its length. One part of it was 17.10mm. This really is borderline for a bearing which has an ID of 17mm. The inner race will jut bind on the shaft stressing out the bearing as the shaft is pulled through. The principle behind Viscount's BB is to make good use of an interference fit (as opposed to a 'disaster fit') between bearing, spindle and frame. Fair enough, but if the spindle diameter is too big it will feel rough to turn when sat within the bearings and the life of the bearings will be drastically reduced. Sadly, in the example of my frame referred to above, the BB must have been rough the day it left the factory!
I would avoid heating up the BB shell unless you are doing it purely for the purposes of fitting the bearings. I would not drive/pull the spindle through the frame UNTIL it and the bearings have completely cooled off! It is essential that the bearings are a snug fit in the frame
. Back in the day the Viscount factory manual procedure for the BB bearings was:
Drive in bearings
Drive through spindle
This is okay as long as the bearings don't come out of the frame as the spindle is being driven through! That really is a major problem!!!!!!! Gotta keep them bearings a tight fit in the frame and have a spindle that taps through (as opposed to being hammered in because it is such a poor fit). It helps enormously if the BB spindle is polished till your fingers drop off before you pop it through the bearings
. I suspect the frame will not need a great deal of heat. A hair drier can be surprisingly effective!! I think powder coating curing is done at around 200 deg. centigrade. Thing is though, this may be too much for the clear coat over the paint.
Spudh wrote:I've ordered SKF bearings this time round which seem to have a good reputation in engineering circles anyway.
I've just had a nightmare with SKF 6003 bearings. The ID was 16.84mm which is very poor
. I only found this out after I tried to establish why the spindle felt so rough to turn by hand. So, whatever bearing you buy, check the ID with vernier calipers before handing over the cash. It seem that there can be some poor variations of tolerances even with stuff considered to be of good quality. It's Japanese bearings for me from now on!
Hope this helps and I hope I am not teaching you to suck eggs! For convenience I tend to assume that everyone is struggling as much as I am