Seat tube cracked, is there a fix?

My seat tube has circumferential cracks 15mm above the top tube joint and 25mm
below the top of the seat tube. The cracks started at the bottom of the
adjustment slot in the back side of the tube. The tube is steel. The cracks
combined are about 80% around the tube. The seat post is set so that the
minimum insertion mark is well below the crack. The bike is a $350 Raleigh,
several years old with maybe 4000 miles.

What is the cause?

Is there a practical fix?

On 4 Apr 2005 20:14:30 -0700, Ed wrote:

My seat tube has circumferential cracks 15mm above the top tube joint and 25mm
below the top of the seat tube. The cracks started at the bottom of the
adjustment slot in the back side of the tube. The tube is steel. The cracks
combined are about 80% around the tube. The seat post is set so that the
minimum insertion mark is well below the crack. The bike is a $350 Raleigh,
several years old with maybe 4000 miles.

What is the cause?

Flexing of the tube.

Is there a practical fix?

The proper fix would be replacement of the seat tube or frame. If
there's enough tube above the joint, a workaround would be to shorten
the seat tube, slot it as far as is practical, file the end flat,
apply touch-up paint, install a stiffer seat post of adequate length,
and continue to ride. From your description, though, I don't think
there's enough of the seat tube to get away with this. I'd start
looking for a replacement frame or bike.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On 4 Apr 2005 20:14:30 -0700, Ed wrote:

My seat tube has circumferential cracks 15mm above the top tube joint and 25mm
below the top of the seat tube. The cracks started at the bottom of the
adjustment slot in the back side of the tube. The tube is steel. The cracks
combined are about 80% around the tube. The seat post is set so that the
minimum insertion mark is well below the crack. The bike is a $350 Raleigh,
several years old with maybe 4000 miles.

What is the cause?

Is there a practical fix?

Is the tube cracked? Or is it just the paint?

I can scarcely imagine a steel seat tube with a properly inserted aluminum post
actually cracking.

Ron

On 2005-04-05, RonSonic wrote:

On 4 Apr 2005 20:14:30 -0700, Ed wrote:

My seat tube has circumferential cracks 15mm above the top tube joint and 25mm
below the top of the seat tube. The cracks started at the bottom of the
adjustment slot in the back side of the tube. The tube is steel. The cracks
combined are about 80% around the tube. The seat post is set so that the
minimum insertion mark is well below the crack. The bike is a $350 Raleigh,
several years old with maybe 4000 miles.

What is the cause?

Is there a practical fix?

Is the tube cracked? Or is it just the paint?

I can scarcely imagine a steel seat tube with a properly inserted aluminum post
actually cracking.

He did mention that the cracks started at the bottom of the slot, which
can be a significant stress riser, particularly if it is not finished
properly. There should be a hole drilled at the bottom of the slot to help
disperse the stresses and prevent such cracking.

Is the frame under warrenty? If so, ask for a replacement. Heck, ask for a
replacement anyway; the worst they can do is say "no."

--

John )

On 4 Apr 2005 20:14:30 -0700 Ed wrote:

My seat tube has circumferential cracks 15mm above the top tube joint and 25mm
below the top of the seat tube. The cracks started at the bottom of the
adjustment slot in the back side of the tube. The tube is steel. The cracks
combined are about 80% around the tube. The seat post is set so that the
minimum insertion mark is well below the crack. The bike is a $350 Raleigh,
several years old with maybe 4000 miles.

What is the cause?

My guess is that the seat post was too small in diameter.

It might be fixable by cutting off that portion of the seat tube and
brazing a new clamp lower down, as part of the seat lug.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Ed Wrote:
My seat tube has circumferential cracks 15mm above the top tube joint
and 25mm
below the top of the seat tube. The cracks started at the bottom of
the
adjustment slot in the back side of the tube. The tube is steel. The
cracks
combined are about 80% around the tube. The seat post is set so that
the
minimum insertion mark is well below the crack. The bike is a $350
Raleigh,
several years old with maybe 4000 miles.

What is the cause?

Is there a practical fix?

A bug-ugly fix would be to grind the afflicted area and then some down
to bare metal, then apply a permanent bandage of carbon fiber strips
bonded with epoxy to maybe 2-3 mm thickness over the cracks and
preferably also extend this some distance on to the top tube as well.


--
dabac

Is the tube cracked? Or is it just the paint?

I can scarcely imagine a steel seat tube with a properly inserted aluminum post
actually cracking.

I could not either but it did. I checked inside the tube to be sure. And the
seat post is the one that came with the bike so it is the correct size. I had
the quick release really tight because when I first got the bike the post would
gradually sink down so maybe that contributed.

I have a Trek 520 which has a heavy clamp that hold the seat post in place
rather than ears welded to the seat tube. If I could find on of those it might
work.

On 6 Apr 2005 19:35:24 -0700, Ed wrote:

I have a Trek 520 which has a heavy clamp that hold the seat post in place
rather than ears welded to the seat tube. If I could find on of those it might
work.

Easy! Lots of places sell them online, and I'd bet that if you aked
at your lbs (make sure you have the figure for the OD of your seat
tube) they would probably either have one in stock or be able to get
it in short order.


--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On 6 Apr 2005 19:35:24 -0700, Ed
wrote:


Is the tube cracked? Or is it just the paint?

I can scarcely imagine a steel seat tube with a properly inserted aluminum post
actually cracking.

I could not either but it did. I checked inside the tube to be sure. And the
seat post is the one that came with the bike so it is the correct size. I had
the quick release really tight because when I first got the bike the post would
gradually sink down so maybe that contributed.

I have a Trek 520 which has a heavy clamp that hold the seat post in place
rather than ears welded to the seat tube. If I could find on of those it might
work.

Dear Ed,

These seatpost clamps may be what you're looking for:

http://www.biketoolsetc.com/index.cg...ost %20Clamps

Carl Fogel

Ed wrote:

Is the tube cracked? Or is it just the paint?

I can scarcely imagine a steel seat tube with a properly inserted aluminum post
actually cracking.


I could not either but it did. I checked inside the tube to be sure. And the
seat post is the one that came with the bike so it is the correct size. I had
the quick release really tight because when I first got the bike the post would
gradually sink down so maybe that contributed.

I have a Trek 520 which has a heavy clamp that hold the seat post in place
rather than ears welded to the seat tube. If I could find on of those it might
work.

That aluminum seatpost collar is easily found at better LBS
in various diameters and styles, silver or black with
integrated quick release or allen bolt.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971