Fitting bottom bracket spacer to adjust chain line ?

BG2000
BG2000 Posts: 517
edited June 2010 in MTB workshop & tech
I need to move the chainrings out slightly on a Truvativ GXP chainset. I'm already using both the 2.5mm spacers to fit the GXP BB into my 68mm shell.

Is it OK to install an additional 1.5mm spacer on the drive side ? I'm wondering if this could cause damage when I tighten the non-drive crank, i.e. is it designed to tighten up against 73mm spaced cups and nothing else ?

Comments

  • nicklouse
    nicklouse Posts: 50,675
    the drive side crank are is designed NOT to be in contact with the bearing or seal.

    to me it sounds like you picked the wrong cogs.

    what was it a big granny and a slightly bigger middle?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • BG2000
    BG2000 Posts: 517
    nicklouse wrote:

    what was it a big granny and a slightly bigger middle?

    Exactly - in fact, a much bigger middle (42T)

    But I now have the perfect gear ratio setup, amazing front gear changing and a great chainline. However the middle chainring is only 2mm from the chainstay.
  • stu8975
    stu8975 Posts: 1,334
    What frame HT or FS? when I did my 40/26 on my FS i actually moved mine inwards by 2.5mm..have about 3mm gap when the bike is un-weighted and prob 6mm when i'm sat on it, had no issues so far.
    ANTHEM X
    Youth
  • BG2000
    BG2000 Posts: 517
    It's a 2009 Cove Stiffee stu8975 (HT).

    So one reason the chainring is tight is due to the wide chainstays (good for mud clearance). Coupled with my large middle ring, it's the worst combination I guess !

    The chain and chainrings are new, so hopefully I won't get any chainsuck. That's my only concern. There's not quite enough gap to cover the RHS chainstay in something tough, like innertube & cable-ties to pretect it in the event of chainsuck. If I could just move the chainset out by a millmeter I'd have space for something, hence my original question.

    RE: the gap between driveside BB cup and crankset - there's more than a millimeter between them, so with the extra 1.5mm spacer, they still wouldn't touch, and hopefully this still meets the design criteria that Truvativ had in mind (which has never been officially documented as far as I can tell, but seems to allow a 'floating' drive-side).

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