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Put a new pedal in, and followed advice not to screw it in too hard. Unfortunately, I made it too loose... and the thread on the right crank is now almost completely stripped because the pedal was moving around and abrading it.

Is there any way to replace just the right arm?

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  • As Batman says, there is a kit that some bike shops use for rethreading stripped crank arms. Visit a few local bike shops and see if any have this. Also check with them for replacement costs. The other option is to find a junker bike with a good crank arm of similar type. Jun 19 '17 at 17:07
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    After you get a replacement crank use the stripped one to bludgeon whoever told you not to tighten the snot out of the pedal. Jun 19 '17 at 18:51
  • Yes, they should be proper tight. But always start gently, and screw them in nearly all the way before using the pedal spanner.
    – Chris H
    Jun 19 '17 at 19:42
  • @mattnz - this is slightly different -- OP proposes getting a different crank as an alternative. So, i'm not entirely sure its a dupe (though the fixing procedure we've said a bunch of times here).
    – Batman
    Jun 19 '17 at 22:44
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Cranksets are typically sold with both arms, not just one of them, so the exercise of finding just a right arm that is compatible is mostly academic (the only case I can think of that's somewhat reasonable is a parts bin at a bike co-op or shop which has one, but this is still unlikely). You're more likely to find the whole crankset instead, in which case there isn't really a reason to not install both of them.

That being said, on a square taper bottom bracket, you can install different square taper crank arms on the left and right (different sizes, different makes, etc). You can mix hollowtech 2 crankarms on the left and right as well. So on, so forth -- the compatibility is determined by what type of crankarm you're running.

If you have an autoshop nearby or a bike shop, you can also try to helicoil the crankset. This puts a new set of threads on for the pedal.

Also, note that if you don't have a crank puller, you're going to have to borrow one or likely go into a shop unless the crank is self extracting.

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  • Lots of good ideas, thanks. Will let you know what works
    – Ne Mo
    Jun 19 '17 at 16:19
  • Since the right hand pedal is normal threaded, an auto shop might be able to helicoil it for you (provided you got the helicoil insert). If it was the left pedal, which is counter threaded, they probably wouldn't have the right helicoil kit for it.
    – Batman
    Jun 19 '17 at 17:29
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    @Batman you mean they wouldn't have the left helicoil kit for it.
    – SQB
    Jun 19 '17 at 20:04
  • Bleh. Right was used as correct in the last sentence if it wasn't clear.
    – Batman
    Jun 19 '17 at 22:42
0

To replace the right arm only, you need to find an arm which matches the left crank length (165 mm, 170mm, 172.5mm, etc), number of bolts as well as the bolt circle diameter (BCD) and axle type (square taper, octalink, Hollowtech II etc.) Its easiest to match like for like but not essential as long as these criteria match the old crank.

When the right arm is removed, the chainrings need to be removed and transferred to the replacement arm. There's a little tool called a peg spanner to fit the back of the bolts. Then the new arm is fitted to the bike and the pedal fitted too.

When you know the crank length, BCD & number off and axle type you can hunt for a new arm, it doesn't have to be exactly the same brand/line. As mentioned you're unlikely to find one for sale on it's own, but maybe second hand online, or hidden away in the kind of local bike shop which keeps such things (i.e. a good one). Bike co-ops etc also

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This is entirely doable, but if you don't have the equipment already, or a reason to do it again, it may be more expensive than buying a new crank arm. Also if you're as unfamiliar with mechanics as you imply, you may have trouble. Note that there's actually a lot of spare metal around the pedal thread. To solve, pick a diameter about 4mm above the current hole. Get a tap (https://en.m.wikipedia.org/wiki/Tap_and_die) of this diameter. Drill out to the suitable diameter for that tap (online charts in same link). Tap (make a thread in) that hole. Buy an aluminium bar of the tap diameter. Use a die (same link) to cut an outside thread on that bar. Screw the bar into the hole using thread lock compound. Cut off the ends. Drill a hole for the pedal thread centrally in the bar (web will tell you correct thread for pedals). Tap that hole also. Finally screw pedal in as before. Unfortunately you will have to buy 2xtaps, 2xdrills, tap holder, aluminium bar, die, die holder and thread lock, and drill perpendicularly. On the bright side, tapping and drilling aluminium is relatively easy.

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    The tooling for doing all this is likely to cost several times more than a new crank arm. At least get a helicoil kit which would be much cheaper. Jun 19 '17 at 21:33
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    Doing this with an aluminum plug is asking for trouble. Helicoil a are made of steel for a reason.
    – RoboKaren
    Jun 20 '17 at 7:14

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