Join Date: Jul 2008
Location: Grid Reference, SK
Bikes: I never learned to ride a bike. It is my deepest shame.
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(the advice below applies to square taper cranks ONLY)
Originally Posted by mtbtrek
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 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.