Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 01-24-09, 04:00 PM   #1
tailwhip169
Member
Thread Starter
 
Join Date: Jan 2009
Bikes:
Posts: 38
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
crank bolt problem on bmx cranks, flattend threads!

hello i have a problem on my bmx profile cranks i recently boght it from somone and the only thing rong with it was it needed some new bolts because the threads had been flattend on the previouse once. So i found some crank bolts on ebay that came from amercia and said fits profile dk and oddsey cranks so obviously i boght them 15. now i have the same problem! i try and twist the bolts in but the threads are starting to flatten again! could somone please tell me why this is happerning i dont know weather to screw this bolts in mega tight nd just leave them there could someone tell me if this would be ok? cheers i have a pic below of the perviouse and the new crank bolts i boght... cheers.here is the old crank bolts...

the new one...


sorry for bad picture quality.. thanks.
tailwhip169 is offline   Reply With Quote
Old 01-24-09, 04:43 PM   #2
frankenmike 
mechanically sound
 
frankenmike's Avatar
 
Join Date: Jan 2007
Location: Dover, NH
Bikes: rigid 29er moto, s-works stumpjumper fsr,black fixie,masi roadbike, ugly old hardrock commuter
Posts: 1,364
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
I have a hunch that there is a chewed up section of threads in the spindle, which shears the tops off the bolt threads as you screw in. If you can find a thread chaser the correct size, run it into the spindle and it should clean up the gnarled section. If you can't find a thread chaser, a hardened steel bolt with a groove cut lengthwise along the thread using a file or hacksaw could work as a chaser. Good luck.
frankenmike is offline   Reply With Quote
Old 01-24-09, 04:45 PM   #3
joejack951
Senior Member
 
joejack951's Avatar
 
Join Date: May 2004
Location: Wilmington, DE
Bikes: 1984 Trek 660, 2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1, 2014 Islabikes CNOC 14 (son's)
Posts: 9,939
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Whatever you are threading those bolts into has damaged threads. It's possible that the tapped (threaded) piece can be cleaned up using the appropriate tap and still have good enough threads to be serviceable, but it's also possible that the piece has been ruined. The damaged threads were likely caused by the bolts being crossthreaded (installed at an angle which caused the threads in both parts to not mesh properly) by the previous owner.

My suggestion would be to take the threaded part to a bike shop (or machine shop if one is available) and have them clean up the threads with a tap. Throw those olds bolts out as they are worthless now and get some new ones. With the threads cleaned up, attempt to install the parts and torque to spec. If everything goes ok, you're good to go. If you it turns out the bolt keeps spinning and won't torque to spec, then you'll need to look into some options for repairing that component.

As a general note, if a fastener won't thread on easily by hand something is wrong. Do NOT attempt to forcefully thread something together using tools as you'll likely damage something. It's a lesson that just about everyone who spends enough time working on mechanical things learns the hard way.
joejack951 is offline   Reply With Quote
Old 01-24-09, 04:58 PM   #4
tailwhip169
Member
Thread Starter
 
Join Date: Jan 2009
Bikes:
Posts: 38
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
thank you i have looked inside th axle and the threads seem pretty clean to me but i shall take to to a bike shop soon as possible.. thanks
tailwhip169 is offline   Reply With Quote
Old 01-24-09, 05:52 PM   #5
tailwhip169
Member
Thread Starter
 
Join Date: Jan 2009
Bikes:
Posts: 38
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
cheers i dont think i have a thread chaser but i could prehaps borrow one from somwear. thanks.
tailwhip169 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:35 AM.