Not all chainring bolts are the same

ed1973
ed1973 Posts: 284
in MTB workshop & tech
I am currently adjusting the chainline and have to push my chainring in around 2mm. I have the spacers but the 2mm increase has meant my chainring bolts now aren’t long enough. I have an SLX M7000 crank that have a useable length of 8mm, but I now need 10mm. Not all chainring bolts are the same as I have found out and the width of these is 7.7mm. Any suggestions out there?

Comments

  • wilberforce
    wilberforce Posts: 316
    Do you have spacers on the drive side of you BB that you can move to the non drive side? That will adjust chain line without faffing with bolts.
  • ed1973
    ed1973 Posts: 284
    wilberforce said:

    Do you have spacers on the drive side of you BB that you can move to the non drive side? That will adjust chain line without faffing with bolts.

    Nope, it’s a press fit, good call though
  • mully79
    mully79 Posts: 904
    I wouldn’t bother for 2mm. I’d try it first.
    If you must try It’s probably worth popping into a local bike shop. They probably have a box in the workshop full of them.
  • reaperactual
    reaperactual Posts: 1,185
    edited February 2022
    What's the rest of the drivetrain set up and is the frame non Boost or Boost? What chainline measurement are you trying to get to?

    Like Mully said, maybe it's not worth the hassle?
  • ed1973
    ed1973 Posts: 284
    Non boost, 54.7mm at the mo, makes my chain move down when I pedal backwards, which bugs the hell out of me 🤣.
  • reaperactual
    reaperactual Posts: 1,185
    edited February 2022
    Wow 54.7mm? Which SLX cranks have that chainline? Yes, maybe you do need to bring it in a bit.

    I've got the non Boost M7000 11-1 crankset on my Boost bike with a 49-50mm chainline and I still get the chain coming off the big cog after about two back pedal rotations.

    P.S. As far as I know the single piece crank bolts on mine are the standard M8x8.5mm and I reckon you should be able to find some longer replacements easily enough. If I was in your predicament, maybe I'd just buy the same crankset I've got.
  • ed1973
    ed1973 Posts: 284
    It is the normal crankset I’ve been using, just changed out the rear mech (and cassette and shifter) to 11 speed and it started jumping off when pedalling backwards. I put the bike together a couple of years ago when I was less experienced (and it didn’t jump off) so thought I’d check stuff now I know kind of what I’m doing. The normal 8.5mm ones simply aren’t long enough to include the spacer. I think I’m gonna try some specialist hardware shops around me, I’d checked Google and the bolts that came up just don’t have the actual measurement I need as the bolt is just the male part that screws directly into the crank and is thinner than the standard male female set up that other chainring bolts come as.
  • reaperactual
    reaperactual Posts: 1,185
    I've got the same male only Shimano T30 crank bolts that came with the crankset, they go directly into the rear of the spider too.

    My cheap ebay chainring also says for M8 bolts, I guess for the mounting hole size and they're snug.

    Even if you find longer bolts I still don't think 2mm further in would sort out back pedalling issue on non Boost bike with a 52.7mm (near enough, still a Boost chainline). 😬

  • ed1973
    ed1973 Posts: 284
    Might just leave it and not pedal backwards. What’s the worst that could happen 😬
  • reaperactual
    reaperactual Posts: 1,185
    edited February 2022
    I suppose it ain't a problem if the chain doesn't derail at the first sniff of going backwards.

    Not acceptable if you're planning on doing what Danny MacAskill does and jumping across rock obstacles etc? 😮

    I guess you might wear your parts out a bit quicker.

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