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Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Section - 8e.11 Stuck Handlebar Stem

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Date: Fri, 11 May 2001 16:35:42 PDT

Frozen aluminum stems were a common occurrence because conventional
stems were poorly anchored in the fork, having only an expander at the
bottom and the top free to pump from side to side with handlebar
forces.  This was OK in the days of steel stems and steel steer tubes
but aluminum accelerated corrosion in this interface, expanding
greatly with oxidation,  in spite of grease in the interface that
only turns to an emulsion in the rain from lateral pumping action.

The expander bolt must be backed off about 1/2 inch to hammer the
expander wedge out of engagement with the bottom of the stem.  When
the expander is free, the bolt should be loose with the expander
dangling on its other end down in the steer tube.  Now the stem should
be rotatable with moderate force.  If this is not the case, then it is
a corroded frozen stem.  Many forks have been damaged by twisting the
bars forcefully in an attempt to free the stem.  Don't do it.  Pouring
ammonia onto the gap is ineffective unless the stem is not truly
frozen.  The thin oxide interface to be dissolved is thousands of
times as deep as thick.  There being no circulation, this method works
only in abstract theory.  

A skilled mechanic can saw off and drill the stem out until it is a
thin shell, then break through one side of the shell with a grinder to
extract the stem.  Because aluminum corrosion expands enough to
stretch the steel steer tube, it cannot be loosened by force.  Riders
often are happy when their stem stops creaking only to find later why
it got quiet.  It was no longer removable.  The main advance achieved
by threadless head bearings is that the stem is no longer subject to
this failure.  It is more a stem improvement than a head bearing
improvement, although it also makes adjustment simpler and less
expensive.

Get it removed by a competent shop.  Frame builders do this regularly.

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Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 3/5
Previous Document: 8e.10 Aligning a Fork
Next Document: 8f Tech Moving Parts

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