Bottom Bracket Selection Guide
Trek BB92 Trouble Part 2: To Ream, or Not To Ream
In this vid we're resizing, or reaming, a Trek BB92 bottom bracket shell that is undersized from the factory. This video is more detailed than videos of the same subject matter previously produced. The purpose is to instruct as well as encourage shops to adopt this as a common practice. Now look, guys, this isn't the time to say bad things about Trek's quality or this or that. Trek makes fine bikes, and we here have owned many. These problems are just part of owning production-line, hand-made products. Get that? One more time: Carbon fiber frames are hand-made, and so the hand-made aspect is a major factor in the outcome regarding tolerances. The good news is these dimensional faux pas are easy corrected, as we shall show you forthwith. Keep an eye out for Vids 3, and 4 in this series and here's the link to Threaded BB install Vid 1
Alright, you guys have seen us use this before this is a 40.98 ream which is what you're gonna use for any BB86 or in this case BB92. I believe this should be industry practice personally. I mean if you're a bike shop you know and you've been around for a while like a long while and you've got a bunch of you know grain hairs in there chances are you've already got one of these and you're already doing this sort of thing you know there's a school of thought oh real quick before i go on to my diatribe there um when you're doing carbon when you're using this for carbon don't put a lot of load on it because I'm not you don't want this cutter to feed very rapidly we want it to be able to dwell for a little while so i just barely put pressure on it like that and I'm going to screw this down just very slightly what this does is put a little bit of spring pressure on it because I don't want to draw this in too quickly if I put if I compress this spring what it's going to do is it's going to make this want to shoot in there very rapidly and the cutters are not going to have time on the contact surface to cut because remember this isn't aluminum so the cutting procedure for this one is a little bit different now I can already tell that I'm cutting quite a bit once again this is 40.98 so as long as you just cut it until it bottoms it'll be perfect so while I'm doing that may I continue so if you if you're not doing this especially with BB92 and BB86 I got to say press fit 30 not really generally necessary bb30 i would say almost never it's really BB86 and BB92 that seem to be the ones that are giving everybody a lot of grief these days as far as having a little issue with the internal dimensions here so as you can see I'm taking this very progressively I'm not just spinning it in there and it's not drawing in rapidly I'm just taking my time cutting it just like that all right I'm almost done now and i should have said this at the beginning you notice that I didn't use any lubricant on here don't it doesn't need it I'm doing carbon fiber all right now all i do is i have a bottoming tap i mean excuse me a bottoming plate right here this tool also you'll typically see it with a facing cutter I have it around here somewhere don't use that because you don't want to cut or you don't want to face at all on this okay you do not want to reduce this dimension that would be very bad uh what you want to do is you just want to ream the inside as I'm doing this side let me just tell you guys the reason why this is so critical especially with BB86 and BB92 is because it's already a 41mm hole and let's just say if I'm putting a Shimano bottom bracket in here or GXP typically you're going to use a 37mm OD bearing 6805 something like that so it actually has quite a bit of structure left you know 41-37 but when you've got when you're putting in a DUB crank or a 30mm spindle you're going to be putting in a bearing that has a 40mm OD so that leaves you a half millimeter of thickness of the actual like sleeve that's going in around where the bearing is pressed into the sleeve that makes sense so you can tell there's not a lot of hedge for really tight frames things like that so they're always going to have a lot of influence on the final outcome of how the bearings perform so if you have something that is really undersized like this one is super undersized okay what it's going to do is it's going to make the bearing not run very well because it's going to have a lot of radial compression because there's no structure of the bottom bracket itself the module to resist that compression and the result's gonna be an over compressed bearing that doesn't spin very well so when we get this to the exact dimension it's supposed to be 40.98 giving us a nice .02 interference fit with our 41mm autograph 41mm outer diameter if I can talk of our module um that's going to give us the fit we want in our next video I'm going to install the bottom bracket
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