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 08-25-08, 05:54 PM   #1
mtbtrek
mtber
Thread Starter
 
mtbtrek's Avatar
 
Join Date: Jul 2008
Location: Earth
Bikes: really nice bike
Posts: 55
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Crank Arm

i have a 06 trek 4900 and the left crank arm felt loose when i was riding so i tightend it and it is always loose. do i have to buy a new one or can it be fixed?
mtbtrek is offline   Reply With Quote
Old 08-25-08, 05:57 PM   #2
Bill Kapaun
Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 9,496
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 125 Post(s)
Once they loosen up, the inner part tends to get "wallowed" out and is toast.
Bill Kapaun is offline   Reply With Quote
Old 08-25-08, 06:07 PM   #3
G piny parnas
messenger
 
Join Date: Aug 2008
Location: WLA
Bikes: pinarellos and a colnago
Posts: 599
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
remove the arm inspect the taper-- look at the arm--- if the aluminum is completely mushroomed-- replace the arm--- check the length and angle--- if it looks kinda Ok-- use a washer and grease the bolt and put it back on--
the washer should sit behind the head of the crank bolt and the lip of the inner arm --- if you are stripping the bolt or the treads on the spindle STOP-- remove and get new....my best shot-- not fact! I assume this is a square taper--- I did this once on an old bike it seemed to work.... that washer forces the arm a bit closer to the stay--- watch carefully
G piny parnas is offline   Reply With Quote
Old 08-26-08, 07:02 AM   #4
LarDasse74
Guest
 
Join Date: Jul 2008
Location: Grid Reference, SK
Bikes: I never learned to ride a bike. It is my deepest shame.
Posts: 3,769
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by mtbtrek View Post
i have a 06 trek 4900 and the left crank arm felt loose when i was riding so i tightend it and it is always loose. do i have to buy a new one or can it be fixed?
(the advice below applies to square taper cranks ONLY)

The arm needs replacing. The press fit of the taper requires very tight tolerances and the slightest deformation will prevent it from ever staying tight on the spindle again.

How can you tell if it is damaged? If it loosens up as you ride, it is damaged. There is no other explanation for loosening while riding.

Also, if you have tried to retighten it a time or three there is probably some damage to the spindle as well.. does the spindle look 'polished' at all? It should be still black (a couple tiny silver streaks on the flat face are acceptable, but anything else and you likely need to replace the spindle as well)

Retightening a damaged arm after it loosens will damage a spindle...
Attaching a new arm to a spindle that has had the old arm retightened will damage the new arm... you can go through several arms and spend quite a bit of money to fix this if you don't do it right the first time.

I usually put a drop of red locktite on the taper flats (NOT on the bolt threads) during assembly. Put grease on the bolt threads. Torque to spec or get an experience mechanic to do it. Overtightening is another easy way to damage the taper of the crank, so make sure this is done properly.

Last edited by LarDasse74; 08-26-08 at 08:59 AM.
LarDasse74 is offline   Reply With Quote
Old 08-26-08, 07:26 AM   #5
mtbtrek
mtber
Thread Starter
 
mtbtrek's Avatar
 
Join Date: Jul 2008
Location: Earth
Bikes: really nice bike
Posts: 55
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
thank you for everything, it is time to go get a new crank
mtbtrek 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 11:41 AM.