22-02-2019, 07:34 PM
If as much as.004 preload is advocated for a.c races surely nil or less clearance for the rear roller ditto is similarly ideal? And as previous, on non racers is spalling or measurable wear of roller ends experienced? Does it worsen with a close fit?
The table in The Companion p119 seems to advocate close tolerance single circle bearings (if obtainable)
As I have stated before my fastidious father replaced main bearings at very frequent intervals. He reckoned he could detect the difference in the various spot ratings, and claimed that the wider clearance were little better than the replaced. Tolerance ranges differed from current.
I have a box full of the old replaced bearings. I have a few C3 bearings inch and metric picked up for a pound or less at swap meets. Seem to be able to roll freely over.003 piece of shim, much the same as the old used bearings.
The difference in tolerance ranges is very small, but Sevens are very sensitive. Modern standard tolerance ranges may differ from those of yore, as do the range for od, id etc. Unmounted clearance Normal 25-50 microns, C3 45 -70. A micron is a millionth of a metre, less than ½ a ten thousandth of inch!
Operating clearance is directly influenced by housing/shaft fits.
It is currently normal to spend up large on Sevens and to sneer at many of the old practices. But I find sorting thru old bearings and mixing parts very close fits can be achieved.
I have asked before but wonder what the experts consider OK for reuse? There must be many situations where wear is negligible, esp with modern oils, garaged cars etc.
I dunno at what clearance use becomes unacceptable as distinct from just traditional bit rough and rumbly.
The table in The Companion p119 seems to advocate close tolerance single circle bearings (if obtainable)
As I have stated before my fastidious father replaced main bearings at very frequent intervals. He reckoned he could detect the difference in the various spot ratings, and claimed that the wider clearance were little better than the replaced. Tolerance ranges differed from current.
I have a box full of the old replaced bearings. I have a few C3 bearings inch and metric picked up for a pound or less at swap meets. Seem to be able to roll freely over.003 piece of shim, much the same as the old used bearings.
The difference in tolerance ranges is very small, but Sevens are very sensitive. Modern standard tolerance ranges may differ from those of yore, as do the range for od, id etc. Unmounted clearance Normal 25-50 microns, C3 45 -70. A micron is a millionth of a metre, less than ½ a ten thousandth of inch!
Operating clearance is directly influenced by housing/shaft fits.
It is currently normal to spend up large on Sevens and to sneer at many of the old practices. But I find sorting thru old bearings and mixing parts very close fits can be achieved.
I have asked before but wonder what the experts consider OK for reuse? There must be many situations where wear is negligible, esp with modern oils, garaged cars etc.
I dunno at what clearance use becomes unacceptable as distinct from just traditional bit rough and rumbly.