Convert BB90 to 6805 bearings?
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  1. #1
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    Convert BB90 to 6805 bearings?

    Iíve seen parts that are supposed to convert a BB90 bottom bracket to 6805 bearings. They are spacers that reduce the bearing ID from 25 to 24mm and that have a flange to replace the original dust cover. The Trek part seems to be PN W326785, and there is also a version from bbinfinite. Has anyone tried this?

  2. #2
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    What are you trying to accomplish? What crank do you want to use?
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    Looking to replace bearings and keep the existing crankset (hollowtech, 24mm). This came up as a possible option when I did research.

  4. #4
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    There is no conversion. The current Trek BB90 bottom bracket w/ steel bearings for Shimano cranks is part# 524555. This is the newest version w/ the plastic reducer/bearing shield you are talking about.
    If your frame has loosened up and you need the 'oversize' bearing kit (37.1mm OD instead of the standard 37.0mm) the part# is 407382.
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  5. #5
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    I went with NSK 6805VV bearings, inserts from bbinfinite, and Loctite 641 retaining compound. So far, so good, and no creaks.

  6. #6
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    Quote Originally Posted by bobf View Post
    I went with NSK 6805VV bearings, inserts from bbinfinite, and Loctite 641 retaining compound. So far, so good, and no creaks.
    What 'inserts' are you talking about? There are bearings, and covers.
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    Quote Originally Posted by cxwrench View Post
    What 'inserts' are you talking about? There are bearings, and covers.
    Their site refers to it as top hat bearing insert.

    https://www.bbinfinite.com/products/...e-modules-pair

  8. #8
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    Quote Originally Posted by bobf View Post
    Their site refers to it as top hat bearing insert.

    https://www.bbinfinite.com/products/...e-modules-pair
    Ok, yeah...that's what Trek does now. What type of tool did you use to install them? Did they go in straight? NSK are good bearings.
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  9. #9
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    Here's my rundown. Probably a lot of it you would already know.

    Bbinfinite sells a kit for this with bearings included. I couldn't tell what kind, so I opted to buy NSK bearings separately. Best selection and pricing I found was at qualitybearingsonline.com.

    At first I tried Trek top hats, but they were pretty draggy under even the least preload. Maybe they are not compatible with older BB90s like mine. The bbinfinite parts appear better-designed for the retrofit job.

    Installation order is bearings first, then top hats, then crankset. The bearings were a close slip fit in my frame. Not the best thing, but at least they aligned well without needing a press. Before assembly I applied Loctite 647 to the OD of the bearings and 7649 activator to the frame cup so they would stay in place. 647 is weak as Loctite retaining compounds go, but I chose to make it as easy as possible to back out of what I was doing. BTW, bbinfinite recommends use of Loctite even when the bearings require a press.

    Once the bearings are installed the top hats snap in by hand. They are flexible so they conform to the alignment of the bearings quite well.

    The crank axle fits *very* snug to the ID of the installed top hats. Which is a good thing, I guess. But even with some grease on the axle, to get it through the BB took some tapping on the drive side with a rubber mallet. (no dents to the hollowtech, thankfully) At the same time I pressed on the outside face of the NDS top hat to keep it from being shoved out of place.

    Fully assembled and with slight preload the BB has no discernible play, and it spins freely. I'm sure the latter means the seals are not waterproof, more like a labyrinth at best. But that's OK with me.

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    Curious why you didn't just use the original style bearings and seal kit from Enduro?
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  11. #11
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    You managed to install the bearings w/o a press of any kind? If so they are no where near as tight as they need to be and you're going to end up with them moving in the frame and making noise. If the bearing fit is 'correct' you definitely need to use a press of some kind to push the bearings into the frame.
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  12. #12
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    Quote Originally Posted by Srode View Post
    Curious why you didn't just use the original style bearings and seal kit from Enduro?
    A mix of things. -I'm just not a fan of Enduro or of trying to solve every case of loose fit with the same oversize bearings. -Also not a fan of pressing steel bearings into carbon fiber cups; Loctite makes more sense to me. -The steel-steel interface of bearing ID against crank axle also bothers me. Seems like it has to slide for crank installation yet be perfectly tight during riding. -Feels good to use a standard bearing that I can buy from the best brands.

    bbinfinite has this blog post, which I found interesting. Of course, it is selling their point of view:
    https://www.bbinfinite.com/blogs/new...blems-solved-1

    I claim no deep expertise here, nor any desire to argue the merits of this approach vs any other. It's interesting though, to see that Trek updated the BB90 to something similar, and now they are moving away from BB90 altogether.

  13. #13
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    Quote Originally Posted by bobf View Post
    A mix of things. -I'm just not a fan of Enduro or of trying to solve every case of loose fit with the same oversize bearings. -Also not a fan of pressing steel bearings into carbon fiber cups; Loctite makes more sense to me. -The steel-steel interface of bearing ID against crank axle also bothers me. Seems like it has to slide for crank installation yet be perfectly tight during riding. -Feels good to use a standard bearing that I can buy from the best brands.

    bbinfinite has this blog post, which I found interesting. Of course, it is selling their point of view:
    https://www.bbinfinite.com/blogs/new...blems-solved-1

    I claim no deep expertise here, nor any desire to argue the merits of this approach vs any other. It's interesting though, to see that Trek updated the BB90 to something similar, and now they are moving away from BB90 altogether.
    Interesting - just for perspective I have a set of Enduro Bearings in my Domane right now that have about 17,000 miles on them, and the frame has about 25,000 miles on it with no problems with the carbon bearing cups or noticeable wear on the crank at the contact points with the bearings. I'll keep using this set up going forward
    Gravel Rocks

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    Niner RLT9 (Gravel Bike)
    BH G7 Disc
    Trek Crockett

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