Tube Dent Repair (Steel Frame)

Recently my favorite bike fell against a handrail post, putting a dent in the top tube. The dent was perpendicular to the tube, over an inch long front to back, and in the center about 3.5 mm deep.  The top and bottom of the dent had raised 'eyebrows'.

Being a steel tube (Reynolds 631), I didn't imagine that it would be a structural issue (especially just doing city riding), but it bothered me to have such a big blemish on an otherwise undamaged frame.

I decided to try to get out as much of the dent as I could, using tube blocks ($14 from Paragon Machine Works).

I greased the top tube well, and clamped the tube blocks onto it 3 times, in different orientations around the tube.  Wanting to preserve the paint, I didn't rotate the tube in the blocks.

The result is that the dent is now much smaller, and the paint is still intact.  It appears that I got out the elastic deformation, leaving only an indentation where the tube wall has actually been stretched (plastic deformation).  Now there are no more 'eyebrows', the dent is just a few mm front to back, and only about 1.5  mm deep at most.

Someday, if I ever get the frame re-painted, I'll first have the remaining indentation filled with brazing rod, but for now I'm satisfied with this result - most of the dent gone, and no painting required.

If you have a similar situation, you might consider doing this, or maybe better, having it done by your LBS (who have probably done it before).

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Permalink Reply by Jim Reho on November 13, 2015 at 6:42am

Very interesting concept, one I had never heard of before.  I had an old Centurion that could have used exactly this, except then it got smushed beyond repair by an eighteen-wheeler.  Thanks for sharing!

Permalink Reply by djm on November 13, 2015 at 7:07am

Ditto.  BTW, what kind of twin-tube frame is in the background?

Permalink Reply by Tony Adams on November 13, 2015 at 11:15am

Steel is real! This is awesome. Thanks for sharing the tip and documenting your experience for us!

Permalink Reply by mike w. on November 15, 2015 at 7:04am

The only big concern about pushing a dent out from the inside (e.g.: a mandrel/seatpost/broomstick, etc, in the seat tube,) is metal fatigue, which could possibly lead to cracking or fracture of the tube. A lot depends on the gauge of tube wall thickness, depth of the dent, and the composition of the metal itself.

i have seen crushed seat tubes (usually caused by over-tight repair stand clamps) repaired by the greased broomstick method when the damage wasn't too severe.

YMMV

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