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keep hearing contradictory stories .some say that standard bearing of nominally the same size available on ebay etc are too thin/thick (forgotten which) and others say no probs. Anyone in the know about this and can confirm the bottom line .
If yes fitting tips/advice would be appreciated.
thanks in advance
bill
If my experience is anything to go by... older style shimano BB's* used the proprietary bearing that are thinner, the latter ones don't. You can replace the later bearing with the generic 6805 bearings & still use the plastic tophats.
Enduro replacement bearings are again a proprietary size, but don't require plastic top hat.
*which there must be a frick load about as I have 5 'old' style and one new style, pity I broke the fricken plastic top hat when I removed it - hair drier to heat/warm it first, before removing, sounds like the answer to that.
There's usually a small difference in the bearing size - IIRC Shimano's are 6mm & standard 6805's are 7mm, so if it's important you can just drop 1 spacer from your BB & chainline is 0.5mm difference. I just didn't bother putting the inner shield back over the new bearings (so just bearing & top hat) & have been running a set of cheapy bearings in there since November with no problem. Repacked em with grease before installation and again when I had a fettle a few weeks back. NDS was looking a bit mucky but DS was untouched.
They seem to work ok for FSA BBs as I've found - which use the same bearing dimensions and axle diameter as Shimano - as far as I'm aware. Got some eBay ones for 98p and thought I'd give 'em a go, they seem to work a treat!
The contradictory stories probably relate to the need for a plastic 'top hat' shim spacer thingy, which you need to carefully save and push out from the old bearings - this plastic 'top hat' takes up the extra space between the conventionally sized bearing and the crank axle. Spare top hats for Race Face bbs are available online - try CRC (about £2) - and should(?) be eaqually compatible.
As for fitting tips... obviously - remove the BB!
Secure it in a vice / work mate
Tap out the plastic 'top hat' shims gently, working from the inside side of the BB cups, with something softish.
Then boot the crap out of the old bearings with a good drift to remove them from the bearing cups.
Find and appropriately sized drift - socket, the old bearings themselves, etc to tap the new bearings in place with lots of grease to smooth things in. Be careful not to apply force to the rubber seals of the bearings. And try to find something that will tap both of the 'metal rings' of the bearings in at the same time (the old bearings themselves are great for this!).
One seated fully, gently tap the plastic 'top hats' in place and she should be good to go!
Hope I ain't teaching you to suck eggs.. 😉