Bottom Bracket Selection Guide
BMX Bike Gets a Serious Reaming
In this video we delve into the root causes of poor bearing performance, taking you step-by-step from diagnosis to confirmation to final correction and performance re-evaluation. This process is applicable across the spectrum of press-fit bicycles be they BMX, road, gravel, MTB, and beyond. If you want to see the FULL step-by-step reaming procedure, check it out here:
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A customer of ours pressed this BB86 bottom bracket into this little BMX bike and I'm feeling the bearing over here and it feels great super smooth but if you come over here the bearing feels very tight and notchy- okay, in order to demonstrate this I'm going to go ahead and pop the crank in here or a crank and I'm going to do a little uh acceleration test to kind of show you guys what I mean by how it doesn't feel that great now BB86 is the same whether it is a BMX bike or a mount- excuse me or a road bike or a gravel bike because BB86 is 41x86.5 now all right I want you guys to see that this thing okay we're not just spinning it you see how it wants to stop down here this is this is the indication that things are not real free. See how that doesn't want to return to zero like that that's your that's your big indication right there that we've got a problem that because it's only tight on one side most likely the bottom bracket itself is out of spec it is uh it's gonna be the 40.98 or so on this side that feels awesome and over here on this side for some reason it's going to be smaller than that so it's putting a lot of pressure on that berries squeezing it like crazy and making it spin poorly so first we need to extract the module in order to measure the frame and see what's going on so I'm going to tighten it in to the frame you've seen some of our extraction videos before but I want to tighten the tool into the frame right so I've got actually a free hand right now I'll try to turn the volume down so I just pulled this out of here and you can take my word for it the bearing feels great now that's always a dead giveaway if you ever remove a module where the bearing felt tight and all of a sudden it feels great again or you remove a bearing from a module or a BB30 frame or whatever and it goes from feeling gritty and horrible to you pop it out and also it feels buttery and great that is a dead giveaway that you have the frame is out of spec is it possible that the bearing could be out of spec you can go ahead and measure it but bearings are precision ground to like four decimal places so they're usually way better to use as a standard than anything else you would have in the shop now for BB86 PressFit to be correct it must be around 40.98 okay that's very specific 40.9798 is the goldilocks zone for a proper press fit now let me show you a little trick that gets played on you when you're measuring a cylinder so you see this right here so our target is supposed to be um basically 40.98 like I said or that or that 1. 1.613 is about what we're looking for so when you come over here this one right now is sitting at 1.6 and zero eight that's not good okay that's way undersized but watch this watch what happens when i this is kind of interesting watch what happens when I turn the tool look at that how'd that happen how can I go like that and it's tight and then I go like this and it's not all right and then I can measure this and then what do we get we're getting almost in spec all right so what's going on? Hole's not round- that's mainly the problem this is very typical of bikes that are welded together even though this cylinder was turned on a CNC machine like our bottom brackets are because it's a cylinder see that, so it's turned very accurately the problem is when you come back in here and you start welding elements to it. It creates stress risers and starts to want to egg out portion of this so that's really what's happened now there's no slag or anything there's no high spots in there as far as like there's not a piece of you know like welded material something that should have been cleaned out this is just a dimensional issue uh with this hole where it's oblong due to um welding stresses during construction and uh you know i didn't get welded um excuse me reamed afterward I would have wanted to do that so we're gonna do it right now I'm gonna put a link down below to the long version of the full explanation on how this reaming process works start to finish so I'm only going to ream the side that was giving us trouble uh that was undersized um the other side I'm going to give it just I'm going to go ahead and run the rim in there a little bit it's really not going to cut anything but just to make sure if there was a high spot or something that didn't detect this will make everything 40.98 no matter what unless it's already bigger than that if it's slightly smaller than that it will cut it off if it's if it's the same size it's going to leave it alone so it's pretty convenient that way I'm up here really close I'm pulling this out right now and I wanted to show you that we had some material removal okay it's bound to happen I mean it was too small so we needed to make it a little bit bigger but that's a substantial amount of material to come out of there I think that's a pretty good explanation for why the bearing wasn't rolling very well it was getting over compressed by quite a bit well after the reaming predictably we are now the correct size so let's go ahead and install a bottom bracket I used cutting oil it's essential to remove all of it now I'm using some white lightning clean straight a shop favorite you can also use denatured alcohol these things are going to be safe on the paint and it's going to do all the degreasing you need it to do and leave no residue do not use acetone brake clean carburetor cleaner anything like that okay like automotive cleaners and whatnot pretty much just use either denatured alcohol or white lightning clean streak and you'll be fine because grease and oil contamination will defeat the retaining compound that we're going to be using even though this is an aluminum on aluminum fit or anodized aluminum to raw aluminum essentially we are going to be using the VibraTite 530 you can also use Loctite 609 but we provide 530 with the modules when you buy them only use this do not use grease to install a PressFit bottom bracket so it should press in with a nice even drag this is the same bottom bracket that was in here so because we obviously want to assess the change that's been made so the original bearings everything are in it's exactly how it was removed from the bike is how it's going to be going or going back in and if for some reason the bearing does get damaged during this process the removal process especially even though our tools are back cut so that that really isn't going to happen if it does happen it's not the end of the world at all the module itself the housing lasts indefinitely and you can always change the bearings out right so uh with aluminum on aluminum fits you don't always get the popping sound that very satisfying and to some people terrifying popping sound you get with press fitting uh because the um because the retaining compound is anaerobic and you're excluding oxygen with a press fit ergo it's starting to light off um doesn't always do that on these but trust me it works all right let's do that acceleration test got our same uh Ultegra crank here so I'm just going to push it in just like that get it in through both bearings and then we're going to okay so you can see you can see the difference already right you notice how it doesn't want to it doesn't want to stop anywhere it doesn't want to stay up on its own in any way whatsoever and it's spinning obviously very freely no problems whatsoever yeah big difference all right well that says it all doesn't it
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