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  1. #1
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    PF30 Eccentric BB, is this normal?

    Got a new bike yesterday that has an FSA PF30 Eccentric BB on it. However, it's definitely off centered in the BB Shell (I think that's what it's called) part of the frame. I know what eccentric means, but it still looks a bit funky.

    Sorry for the bad pics.

    Thanks for any help.






  2. #2
    coprolite fietsbob's Avatar
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    has an FSA PF30 Eccentric BB on it. However, it's definitely off centered
    pretty much the definition of Eccentric .. its there to create chain tension for IGH & Belts..

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    Old fart JohnDThompson's Avatar
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    Yup. "Working as designed." /thread

  4. #4
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    Pretty much what I figgered, but just wanted to be sure. This bike is set-to-jet then.

    Thanks guys!

  5. #5
    Andrew R Stewart Andrew R Stewart's Avatar
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    If the eccentric is to allow for chain adjustment (and most are) then a good one will have just over 1/2" of adjusting 'throw" (or is it "swing"?). Andy.

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    Yeah, it's on a single speed, so definitely for chain adjustment. I had just assumed that the entire face of the BB shell would be covered and was suprised when I could see a bit of lip around the outside. That's all.

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    biked well well biked's Avatar
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    Just curious...what bike is that? I've not seen a singlespeed w/PF30 eccentric bb before.

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    It's on a Raleigh Furley. The bike has vertical dropouts and a spacer kit on the rear hub, so that if you ever want to run it geared, it's plug and play (though I never will), hence the eccentric BB.

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    biked well well biked's Avatar
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    Quote Originally Posted by Shinkers View Post
    It's on a Raleigh Furley. The bike has vertical dropouts and a spacer kit on the rear hub, so that if you ever want to run it geared, it's plug and play (though I never will), hence the eccentric BB.
    Thanks.

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    I don't understand why the BB shell needs to be open like that. Couldn't a full coverage disk with an off center hole for the BB spindle be used to cover the opening and rotated to give the adjustment needed? Perhaps it could be indexed or splined on the edge to match similar tooth-like features on the BB shell and keep the disk properly oriented. Having the spindle permanently attached to the DS crank arm would assure that it stays straight, i.e. has the same orientation on both sides of the BB.
    Robert

    "Wish I didn't know now what I didn't know then." (Bob Seger, "Against the Wind")

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    When I first heard of an eccentric BB, that's exactly what I was thinking of, an off center hole for the BB that would be rotated. So I was a bit perplexed by seeing the face of the shell a bit. I just picked the bike up from the shop and when I got home I noticed it when I was looking the bike over a bit more.

  12. #12
    Andrew R Stewart Andrew R Stewart's Avatar
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    Wow, you guys have far better eyes then i do. How you can see any details form the photos posted is beyond me. On my monitor they're really fuzzy, dark and pretty poor. Andy.

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    Quote Originally Posted by Andrew R Stewart View Post
    Wow, you guys have far better eyes then i do. How you can see any details form the photos posted is beyond me. On my monitor they're really fuzzy, dark and pretty poor. Andy.
    Sorry about that. They're cell phone pics. When i get off of work I'll get some better ones.

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    Alright here ya go. You can see a bit of the BB shell's face. Both sides are the same.











  15. #15
    Andrew R Stewart Andrew R Stewart's Avatar
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    Ah! The fog lifts And now i can ask how the eccentric is held in place. Not by a binder slot and pinch bolts on the frame's shell. Does the eccentric have an externally expanding element? A wedge, or "brake shoes"? Or do the two ends clamp the shell's faces with drawl bolts running from "cup" to "cup" (like the "American/i pc shell adapter to an English 3 pc crankset has)? Andy.

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    And that's where I'm gonna be no help at all . I know there are not pinch bolts on the frame, but after that, I couldn't say (I do not know much when it comes to certain parts of a bike [yet]).

    Actually, I just found this:http://www.bikeradar.com/us/news/art...adapter-36683/ That looks identical to what I have, and looks like the bit of BB shell that's showing would definitely be normal.

    Also this: http://www.fullspeedahead.com/produc...ENTRIC-ADAPTER
    Last edited by Shinkers; 02-08-14 at 05:46 PM.

  17. #17
    Andrew R Stewart Andrew R Stewart's Avatar
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    Yes, these links are of the last style of eccentric that i described. You'll likely need to pull the crank arm on the side of the drawl bolt heads to get access to them. This style does loosen and move easily (after loosening the bolts), unlike some other types (found on tandems). However since the BB unit spans the two "cups" of your type, yet these "cups" are not otherwise tied together, care must be given to the BB unit's alignment after adjusting of the eccentric. Andy.

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    But it looks like no matter what way I turn it, there will always be a lip on one side of my shell, correct? That's how it's designed? My chain tension right now is just fine (just bought the bike), I just wasn't sure about seeing that lip.

  19. #19
    Andrew R Stewart Andrew R Stewart's Avatar
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    Well the inside face of both "cups" will touch the shell faces. And it looks like the shell will have a small section of its face not covered by the eccentric. As long as the section not touching is a minor portion of the circumference all is well.

    BTW these eccentrics (of any type) like frequent servicing. Cleaning of mating surfaces, retightening and the like. There are lots of stories of creaks from eccentrics. Andy.

  20. #20
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    Yeah, it's only the very bottom section of the shell shown in the pics that's exposed. So it sounds like we're all good, I just need to be aware that it will require more maintenance that regular BB's (which I will need to learn to do ).

    Thanks for all the help.

  21. #21
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    it looks like you have external bearings on your BB, it's common, and maybe inevitable, that the center of the BB shell and the spindle, and hence the bearings will not be concentric.

    i think i've seen some oversized BB shells, that are designed for eccentric spindles, that have internal bearings. the edge of the BB shell and the bearings are flush. in that case, i think, the mismatch between the BB shell and the spindle bearings can be and is hidden.

    i'm no expert on eccentric BBs but i do have a couple of eccentric rear hubs and one uncle that is . so i may well be wrong about this. not about my uncle though. everybody in the family is in agreement...

  22. #22
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    Okay, think I got it figgered out now. A regular PF30 BB is going to leave the face of the BB shell exposed already anyway. It's the [cup?] on the FSA Eccentric adapter that's off center and overlaps a bit on one side. Seems to all make sense now. At least that's my take.

    Thanks guys.

    Now if only there weren't paint chips missing on the face of the shell from whoever installed it... .

  23. #23
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    Andy Stewart made a comment- "care must be given to the BB unit's alignment after adjusting of the eccentric. Andy." that can't be emphasized strongly enough.

    After adjusting the eccentric for chain tension, it's critical that both sides be in perfect alignment or you will have bearing problems. Since we don't see the eccentric/brg cups exposed we can't tell if there is some method of indexing the two cups for alignment. If it's just the drawbolts... Make sure the cups are free to spin easily with the BB shell (remove corrosion, clean and grease) so the cups spin easily for minute adjustments. How do you know if they are aligned? After adjusting and clamping the shells pull the crank and re-install. If it slips in easily you're good to go.

  24. #24
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    It looks to me though, like the two drawbolts would index the adapter's cups wouldn't they? So they'd either be aligned, or opposite each other completely (which mine are definitely not). Sorry, I'm new to this stuff and some of it is getting a bit over my head.

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