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  1. #1
    Senior Member surreal's Avatar
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    crankset help... stripped female threads for grannie ring

    hi there

    just got a cool old bike with a cool old shimano deore biopace crank. i found a bolt for the granny ring was missing. i took out one of the other bolts, and headed to the hardware shop to look for a replacement. couldn't find one. rode home, tried to replace the one bolt into the hole that'd been empty, and it's stripped. i really want to keep the cranks, b/c they're cool. have i any cheap way of saving this crank? helicoil kits are $40, and i've never used one; i worry that i'd eff it up. should i get a NOS crank? A set of sugino xd crank arms? or is there a cheap way to keep the oe crankset?

    thanks
    -rob

  2. #2
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by surreal View Post
    hi there

    just got a cool old bike with a cool old shimano deore biopace crank. i found a bolt for the granny ring was missing. i took out one of the other bolts, and headed to the hardware shop to look for a replacement. couldn't find one. rode home, tried to replace the one bolt into the hole that'd been empty, and it's stripped. i really want to keep the cranks, b/c they're cool. have i any cheap way of saving this crank? helicoil kits are $40, and i've never used one; i worry that i'd eff it up. should i get a NOS crank? A set of sugino xd crank arms? or is there a cheap way to keep the oe crankset?

    thanks
    -rob
    Darn- those are nice old cranks. I'd take off the granny ring and see if there's any threads left in the bottom of the "stripped" hole. If there are, find a longer bolt (probably from an old-style triple, where the bolt goes through all three rings) and see if it'll hold the granny ring in place without bottoming. If it does bottom, you can start shortening the bolt a couple threads at a time (a bench grinder works nicely) until the bolt holds the granny in place properly.

    I've been through this- saved a old crank and got a few more years use out of it.
    Jeff Wills

    All my bikes.

  3. #3
    Senior Member surreal's Avatar
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    Quote Originally Posted by Jeff Wills View Post
    Darn- those are nice old cranks. I'd take off the granny ring and see if there's any threads left in the bottom of the "stripped" hole. If there are, find a longer bolt (probably from an old-style triple, where the bolt goes through all three rings) and see if it'll hold the granny ring in place without bottoming. If it does bottom, you can start shortening the bolt a couple threads at a time (a bench grinder works nicely) until the bolt holds the granny in place properly.

    I've been through this- saved a old crank and got a few more years use out of it.

    This is excellent advice, if only i can find the right bolt... This crank, as you may know, is of the type with the spacing washer between the granny and the spider. The bolts are fairly long as it is. i think i can figure out if there are any threads near the bottom by simply revoving the crank and the granny, and using one of the existing bolts to see if it can grab any threads. I believe i'll do that now.

    -rob

  4. #4
    Senior Member surreal's Avatar
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    harris cyclery has the bolts i'll likely need. $13/set. i think i will have to make sure there's any threads first...

    -rob

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    If 4 out of the 5 bolt holes are OK, you can get away with super gluing the stripped one in place.

    Clean the bolt hole with acetone using cotton balls held with tweezers and be sure to do a thorough job. Also clean the face where the chainring will mount, and the corresponding spot on the ring. Mount the granny using the 4 good bolts and tighten (don't strip these). Now apply some super glue into the bolt hole, insert the last bolt and spinn it to spread the glue and use a C-clamp (have ready in advance) to hold the bolt and chainring tight to the face of the crank. Allow it to cure for a while and enjoy your repair.

    It won't last forever, but you'll be able to get use out of a crank you might otherwise throw away, without sinking dough into it.
    FB
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    Senior Member surreal's Avatar
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    Fb, i appreciate your adhesive advice, but i'd rather not do something quite so permanent on a crank, even if the thing is essentially doomed anyway... It'd probably work for someone with less OCD than I got.

    I removed the right crank, took off the granny, and inspected the threads. The threads appear to be intact only a few mm down from where they begin. However, they seem to be damaged at the point of engagement: cross-threaded, i reckon. I may be able to retap it, but i bet a good tap would cost more than the cranks are worth.

    I'm thinking this crank may live on, in a future single-ring project. I've got another one of those on the horizon...

    My travels on the interwebs has led me to ebay, where i got a new/unused rear/right sugino xd tandem crankarm for $1.99. Of course, this is ebay, so it'd $13 shipping. Still, $15 is less than half of what everyone else gets for 'em online. Next time i order from treefort, i'll grab the left arm for $17. Use the biopace rings on the XD. Practice my polishing skills on the semi-stripped deore crank while i scheme on my next project.

    Thanks for the help, guys. =D
    -rob

  7. #7
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    If you've got good threads deeper, but still within reach of the bolt and the problem is that you can't get the bolt started straight because damage to the initial threads, than saving the crank is easy.

    Drill, ream or file out the damaged threads to allow the bolt to go in straight and engage the good threads. If you have more thread depth than your bolt uses, get a longer one, and cut it down to the maximum usable length.
    FB
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    Senior Member surreal's Avatar
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    Quote Originally Posted by FBinNY View Post
    If you've got good threads deeper, but still within reach of the bolt and the problem is that you can't get the bolt started straight because damage to the initial threads, than saving the crank is easy.

    Drill, ream or file out the damaged threads to allow the bolt to go in straight and engage the good threads. If you have more thread depth than your bolt uses, get a longer one, and cut it down to the maximum usable length.
    I'll have to try to do that... Thanks.
    -rob

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    Senior Member surreal's Avatar
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    ..
    Last edited by surreal; 11-14-10 at 09:38 PM. Reason: double post double post oops oops

  10. #10
    Senior Member BCRider's Avatar
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    On the off chance that there isn't enough thread at the base of the hole start phoning around to bike shops to see if they have a helicoil setup. If you don't have any luck start phoning the motorcycle shops. I'd be shocked if a motorcycle shop can't do it for you or can't recomend the machine shop that they get their stuff helicoiled at. They DO run into stripped metric threads on a regular basis so they have to have the stuff or a shop for dealing with this issue.

    Best of luck with the wobbly wings....
    Model airplanes are cool too!.....

  11. #11
    bike whisperer Kimmo's Avatar
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    Quote Originally Posted by surreal View Post
    The threads appear to be intact only a few mm down from where they begin. However, they seem to be damaged at the point of engagement: cross-threaded, i reckon. I may be able to retap it, but i bet a good tap would cost more than the cranks are worth.
    You can turn an old bolt into a tap, you know...

    Grind a bit of a taper onto the end, then cut some slots into the threads with a dremel's cutting disc.

  12. #12
    Senior Member BCRider's Avatar
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    Good idea Kimmo. And you don't need a Dremel for this A regular metal working file does a superb job of cutting the gullets needed to turn a steel bolt into a thread chaser for this sort of use. The trick is to get it started truly so it "flows" into the intact threads.
    Model airplanes are cool too!.....

  13. #13
    bike whisperer Kimmo's Avatar
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    That's the trick with any tap, but these home-made bodgies generally require a bit more patience and precision again...

  14. #14
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    The issue isn't necessarily getting or making a tap, but picking up a good lead. Often when dealing with damaged or crossed threads it's hard to get the tap started straight as it will want to pick up the crooked lead of the first thread and extend it. That's why it's good practice to remove or open up the first thread, or in the case of a through hole like a crank arm, to tap from the opposite side so the tap moves from good thread to bad.
    FB
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    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  15. #15
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by surreal View Post
    Fb, i appreciate your adhesive advice, but i'd rather not do something quite so permanent on a crank, even if the thing is essentially doomed anyway... It'd probably work for someone with less OCD than I got.

    I removed the right crank, took off the granny, and inspected the threads. The threads appear to be intact only a few mm down from where they begin. However, they seem to be damaged at the point of engagement: cross-threaded, i reckon. I may be able to retap it, but i bet a good tap would cost more than the cranks are worth.

    I'm thinking this crank may live on, in a future single-ring project. I've got another one of those on the horizon...

    My travels on the interwebs has led me to ebay, where i got a new/unused rear/right sugino xd tandem crankarm for $1.99. Of course, this is ebay, so it'd $13 shipping. Still, $15 is less than half of what everyone else gets for 'em online. Next time i order from treefort, i'll grab the left arm for $17. Use the biopace rings on the XD. Practice my polishing skills on the semi-stripped deore crank while i scheme on my next project.

    Thanks for the help, guys. =D
    -rob
    Here's your tap if you want to go this route:
    http://www.biketoolsetc.com/index.cg...item_id=MS-TST
    Item #MS-TST: .For chasing inner chainring threads on triple cranksets, High Speed Steel, M8 x .75

    I'd recommend getting a Bike Tools Etc. catalog. Good reference, and good stuff.

    FWIW: I dug out my Deore crank from my bin o' parts. Right now it's got one chainring on it, along with a bashguard. One of these days I'll build a grocery-getter around it. That's how I do bike projects.

    Careful with the XD crank- sometimes the square tapers are oriented differently for different brand cranks. If you combine the Shimano left arm and Sugino right arm, you might end up with a 45 degree offset. That makes pedaling pretty tough.
    Jeff Wills

    All my bikes.

  16. #16
    Senior Member surreal's Avatar
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    jeff-

    that tap might be perfect, plus i wanted to order some sturmey shhh from them anyway.

    thanks to all for advice on the bolt-as-tap thing. i can be patient, and i can be determined, but i don't always get "precise". i think i'm better off dropping the $7.50 on the tap. good to know there's a macgyver option too, though

    the xd crank, should i use it, would get a matching xd left crankarm. the angle and q-factor is def different than the shimano deore crankarms. pretty sure the 113mm spindle on the existing bb will work nicely, though...

    thanks again
    -rob

  17. #17
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by surreal View Post
    hi there

    just got a cool old bike with a cool old shimano deore biopace crank. i found a bolt for the granny ring was missing. i took out one of the other bolts, and headed to the hardware shop to look for a replacement. couldn't find one. rode home, tried to replace the one bolt into the hole that'd been empty, and it's stripped. i really want to keep the cranks, b/c they're cool. have i any cheap way of saving this crank? helicoil kits are $40, and i've never used one; i worry that i'd eff it up.
    Most decent shops should have helicoil kits.

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