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  1. #1
    mtbr member
    Join Date
    Jul 2006

    External BB installation, chainline and FD compatibility

    Hi all!

    This is my first post here. Please be gentle...

    My current bike is an LHT I built up about a year ago. Did everything myself, including BB and HS installation, as well as building the wheels. It's been absolutely great for a year and there have been no issues. So, I have had successful experiences building a bike.

    What brings me here then? Well, after a couple of years riding on the roads, and with fall and winter approaching (fair enough, it's the middle of July still, but hey...) I suddenly got the urge to build myself a heavy-duty multi-purpose fully rigid fat-tyred MTB.

    I love my LHT and I love the attitude and style of Surly's other bikes, so going there for the frame was a given. And since I seem to fall in love with beefy and odd objects, the Instigator was the only option! The fact that I already have an Instigator fork only added to my determination.

    Once built, it will have 2.5" wheels and a fair mix of other components. 11-34 cassette and a 44/32/22 crankset. My estimate, based on available weight data for the parts, is that it will end up at about 33-34 lbs. Maybe a pound more or less, but not more than that. Yes, I know that's heavy for a fully rigid bike, but my LHT weighs 27 lbs "empty" (33-34 lbs with my usual load of spare tubes, pump, basic tools, and so on...) and I'm pretty light myself at 140-145 lbs, so it's not a major problem. I won't be racing or anything. Just riding around off road at my own pace.

    I haven't ordered the frame yet, or indeed any other parts for the build. I'm still in the process of nailing down which parts to get. I've got most of it now, but the BB/crankset is still a bit of a problem...

    The main problem is really a lack of information/specifications for parts, coupled with stupid Shimano compatibility (or lack thereof).

    My first choice was to go with a Deore 530-level crankset, since that's what I have on my LHT, but the next problem then was the incompatibility between ES70 and ES50 BBs. Specifically, the 121 mm spindle length the Deore crankset requires, vs the 118 mm which is the longest available ES70 spindle. From my experience with the LHT build, I know that using a too-short spindle length causes FD reach problems - the FD can't shift down to the granny!

    The reason I don't simply go with an ES50 BB is that the non-drive-side cups are plastic, and I messed up the plastic one I got for my LHT. Fortunately, I still had the metal ES70 NDS cup, so I used that one instead. But the problem with the plastic cup made me want to avoid them in the future.

    So, instead, I looked at the Hone crankset. A bit more expensive than a ES50/Deore 530 combo, but not by too much. The ability to remove cranks/chainrings, for modification or cleaning, without much effort and with only standard tools, also appeals to me.

    But the problem with the Hone is the fact that it has external bearings. Which supposedly require a properly faced BB shell. I don't have the tools to do that myself, and I know from last year, with my LHT build, that none of the shops within my reach have the tools either. So, facing the shell is unfortunately out of the question. And my question then is if that means the external bearings are also out of the question?

    My LHT had pretty smooth and parallel BB shell and HT faces. I simply carved the paint off and found a nice surface underneath. But one example doesn't mean much. Maybe I was lucky and most Surly frames are actually less than perfect in this regard?

    I understand the design and operation of the external bearing system, as well as the potential implications of an imperfect installation (non-parallel bearings), but how much of a problem is it in practice? I'm by no means a heavy rider, and I won't be doing any really hard riding on it (which will have some of you wonder why I insist on getting one of the heaviest frames around...), so how likely is it that I'll break the spindle or something else, with an incorrectly installed external BB system?

    Another thing. Knowing that the chainline is a bit off already on my LHT, I wonder what the chainline will end up at with a Hone crankset on the Instigator. Anyone have that setup, or chainline specs for the Hone?

    Long post, I know... Sorry!

  2. #2
    mtbr member
    Join Date
    Jul 2006
    Nobody knows or nobody cares?

  3. #3
    mtbr member
    Reputation: ctracer01's Avatar
    Join Date
    Oct 2004
    you'll be fine w/ an external BB

    cases of BB misalignment are few and far between, chances are pretty rare you'll have a problem. especially wouldn't worry about it buying a surly. yea chainline won't be great but...just learn to shift better : )

    i have no idea what BB's you're talking about w/ all the #'s and i'm too lazy to look them up so....yea

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