In 1950 bearing manufacturers were capable of equivalent degrees of accuracy to modern manufacturers...'C3' clearance relates to the internal clearances of the bearing (measured in microns), not its outside diameter or inside diameter so the degree of fit to the hub and/or spindle would be unaffected by the change from the standard specification. Only the internal fit after installation would be affected....Tolerances for the hub and spindle produced by BSA would have been such that a consistent fit was achieved...
Personally I never use bearings from Chinese manufacturers due to concerns regarding their quality so my first inclination would be to check the originals against a 'branded' bearing from a recognised European, Japanese or American manufacturer...The bearings originally used were 'stock' bearings with no special characteristics dimensionally and you shouldn't have replacement problems.....Ian
Yes I am aware that C3 refers to the internal clearance and nothing to do with the bearing dimensions. For a bearing this size a C3 would have .00005" more clearance than normal. I was hoping this would allow the bearing to spin more freely then the regular clearance. It did not!
And I think you are missing my point that the OD of the original Hoffmann bearing is supposed to be 2" but is 1.9987" which is a lot smaller (.0013") than it should be. It was measured with two different calibrated micrometers.
Why is it smaller, I don't know?
The China bearing took a lot more force to press it in the hub than the original one and it was for all practical purposes exactly 2". Even with only one bearing pressed in you could feel it was getting stiff to turn. I don't have another hub to measure so don't know what the bore dimension should be.
Were this bike a Velocette, I would expect these kind of problems as they were famous for not scrapping out of tolerance parts and doing what was necessary to make them fit.
But I have a problem believing BSA would do this.
Next time the bearings need to be greased, I will try to find some not made in China. Probably won't be easy to find sealed ones not made in China as being a imperial size bearing there is not a lot of demand for this size anymore.
