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I have an old "Favorit" racing bike from Czechoslovakia and I'm missing some bolts on the chainring. I went trough some bike shops and couldn't find a replacing one. The bolts diameter is slightly smaller on mine which make the new unable to fit.

Crankset with screw Screw size

I would like to keep the "style" of my bike as intact as possible. I can see two options here:

  • Find a website with such old chainring bolts (if anyone got any tips here, I've been pretty unlucky so far)
  • Make the hole in the chainring slightly bigger (by using a file?).

What would you recommend? Would option 2) be even possible?

Thanks in advance!

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    This might fit the bill. I don't know the generic terms for these so I didn't put it down as an answer. ebay.com/itm/… – Noah Sutherland Feb 26 at 1:19
  • To me they look like 9mm dead. What can you get easily? In what material? Do you have access to a lathe? I'm thinking turn down an equivalent sleeve bolt – Chris H Feb 26 at 16:19
  • @ChrisH Thanks for your comment! They're indeed 9mm but it seems that the bolts produced nowadays are 9.1mm. I sadly do not have access to a lathe... – user2225177 Feb 26 at 16:46
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If you want to enlarge the hole to fit current 9.1mm bolts as in the comments, you could use a reamer (wikipedia) available in 9.1mm. This second link is to one meant for machine use, but you can buy hand reamers and probably get away with using this one by hand (and is the first clear link in a google search for "9.1mm reamer"). You can probably find one cheaper but for steel parts you'll want a carbide tool (and I don't know how special the bike is or how much you want to spend).

A reamer is designed to remove minimal material very cleanly, so will maintain both the circularity and the centration of the hole.

You can get 9.1mm drills, and you'd almost certainly get a good enough cut with one, but if you're buying a tool, buy the right one IMO.

If you had a lathe I'd say use stainless bolts and turn a tiny bit off them.

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    Thanks! I ended up drilling the hole to 9.1mm, worked out fine. – user2225177 Mar 1 at 7:53
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I recommend against filing out the bolt holes. You will not be able to get to holes round enough with a file and the bolt surfaces will not engage with the crank properly. You could try drilling the holes slightly bigger but I'd still be worried about getting the hole diameter accurate enough.

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