Crank spider chain contact- Mtbr.com
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  1. #1
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    Crank spider chain contact

    I am in the process of building my first single speed and I recently picked up a Blackspire 32 tooth 104 BCD single speed chainring to use with a Shimano M542 Hollowtech II crank that I had laying around.

    After installing the chainring on the inside of the spider I immediately noticed that the spider sticks out beyond the ridge into the teeth of the chainring. I tested with a chain and sure enough the chain rubs the top points of the spider as the crank turns. I then tested the same ring with an older XT crankset and the same issue occurred (pictured).



    I'd rather not wear a groove into the top of my spider if I can avoid it, has anyone else encountered this issue and if so how did you solve it? Do I need to purchase a different chainring from a different manufacturer?
    Attached Thumbnails Attached Thumbnails Crank spider chain contact-img_0221.jpg  


  2. #2
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    wow, that's really weird. The only thing you can do without grinding the spider down a little is get some chainring bolt spacers or something. I'd imagine it would loosen up on you though. Have you tried running the ring on the outer side to see if it may clear? Shimano should replace that as it is clearly an out of tollerance forging.

  3. #3
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    I'd just get file and take off only enough to give you chain clearance - it's only five minutes work and isn't going to adversely affect the integrity of your crank.

  4. #4
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    should you get Shimano to replace it under warranty, with a time frame of at least 2 weeks, or should you file it down in 5 minutes? TOUGH ONE.

    grind the sucker down and go ride.

  5. #5
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    Thanks for the responses, I have tried the outer side and the same issue occurs.

    I think the cranks are ok since both the M542 and XT work fine with the stock Shimano chainrings without any clearance issues.

    I'm going to see if I can find a different 32 tooth chainring today and see if that changes anything but if they all have the clearance problem I'll break out the file.

  6. #6
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    I would be very surprised if a different chainring makes a difference. Because chains have a fixed spacing between links, chainrings all have to be the same size for any given number of teeth

  7. #7
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    Moving the ring from the inside of the spider to the outside of the spider won't change the size of either the ring or the spider, so of course the situation will persist. As it will with any other ring of the same size.

    Grind the spider. I've done it before... no problem whatsoever.

    --Sparty
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    We get old because we quit riding.

  8. #8
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    Quote Originally Posted by Sparticus
    Moving the ring from the inside of the spider to the outside of the spider won't change the size of either the ring or the spider, so of course the situation will persist. As it will with any other ring of the same size.

    Grind the spider. I've done it before... no problem whatsoever.

    --Sparty
    since it's forged, it could have a bit of a draft angle to it, which could be just enough to clear the chain. Longshot, but worth checking. I didnt know how off it was.

  9. #9
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    Quote Originally Posted by boomn
    I would be very surprised if a different chainring makes a difference. Because chains have a fixed spacing between links, chainrings all have to be the same size for any given number of teeth
    For a 32 tooth sprocket I think it should be 121.64mm, measued diametrically from base of tooth to base of tooth (although ISAR will know more about this than me, I guess).

    At least then you could check if your sprocket was undersize or not, although even if it was, the chain couldn't follow the smaller rad. anyway.
    Does the chain that you are using have very deep sideplates ?

  10. #10
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    Quote Originally Posted by Andy R
    For a 32 tooth sprocket I think it should be 121.64mm, measued diametrically from base of tooth to base of tooth (although ISAR will know more about this than me, I guess).

    At least then you could check if your sprocket was undersize or not, although even if it was, the chain couldn't follow the smaller rad. anyway.
    Does the chain that you are using have very deep sideplates ?
    yea, close enough. most side plates i've measured are nearly 1mm larger than the roller, so it would need to be about 120.5mm to clear the chain.

  11. #11
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    Quote Originally Posted by azmtbkr81
    Thanks for the responses, I have tried the outer side and the same issue occurs.

    I think the cranks are ok since both the M542 and XT work fine with the stock Shimano chainrings without any clearance issues.

    I'm going to see if I can find a different 32 tooth chainring today and see if that changes anything but if they all have the clearance problem I'll break out the file.
    Since the OEM rings fit, I'm thinking it has to do with the width of your SS chainring (.16) and the chainring bolts. I can't tell from your photo, but you should have mounted your chainring with the countersunk side out, so when you mount the chainring, a portion of the female chainring bolt extends far enough to center the chainring on the spider. Since you are mounting the chainring on the inside, this means the graphics on the chainring will be facing inward. If not your chainring will be off center and maybe causing your problem. It's the first thing I thought of

    edited: of course the oem rings are also spaced away from the spider arms.
    Last edited by aka brad; 07-03-2010 at 08:48 PM.
    Just one more rep and I get the toaster!

  12. #12
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    Quote Originally Posted by ISuckAtRiding
    yea, close enough.
    Thanks - that (121.64mm) is what I'd work to anyway.

  13. #13
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    Quote Originally Posted by Andy R
    Thanks - that (121.64mm) is what I'd work to anyway.
    121.631675mm is what the software says, so 121.64mm i'd say is close enough

  14. #14
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    Quote Originally Posted by ISuckAtRiding
    121.631675mm is what the software says, so 121.64mm i'd say is close enough
    What's this "software" of which you speak ? You youngsters are getting lazy

    I'm still using my 1968 edition of "Machinery's Handbook" for stuff like this

    (My father bought it for me the year that I started my apprenticeship.)......

  15. #15
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    Quote Originally Posted by Andy R
    What's this "software" of which you speak ? You youngsters are getting lazy

    I'm still using my 1968 edition of "Machinery's Handbook" for stuff like this

    (My father bought it for me the year that I started my apprenticeship.)......
    i used to do everything out by hand until i went through the state apprenticeship program back in CT. I was determined to finish the placement test without error so i could save myself a few years, and you couldnt use a calculator. I was so burned out after the test that i went and bought myself a calculator and never looked back lol
    I do have a 12th edition Machinery's Handbook somewhere around here but i havent opened it in years. I taped a copy of the triangle formula page to the back of my calculator and that's about all i need out of it. Damn us we lazy youth!

  16. #16
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    I've got exactly the same problem on my rig. Just put two different rings on and both catch.

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