Seat tube crack - advice wanted

renaldo · May 15, 2010

While cleaning my bike I noticed a crack in the seat tube just above the join with the top tube that seems to go into the weld. It doesn't seem to have gone all the way through the tube but you can see and feel it both inside and outside the tube - I've tried to show this in the photos and have taken some before and after I've cleaned it up a bit.
I've taken it to my local bike shop and they think being steel it can probably be fixed and suggested I take it to Chas Roberts who aren't too far away. Has anyone else had any experience of this, and what is the prognosis for my bike?

Thanks,

Ross

cchris2lou · May 15, 2010

yes , if it is steel , sould be easy enough to fix by a frame builder .

Steve Kish · May 15, 2010

Agreed. Might be worthwhile fabricating a collar and welding that on for additional strength.

brocklanders023 · May 15, 2010

From what I've heard Chas should be able to sort it no worries.

renaldo · May 16, 2010

Thanks for the responses guys. I'm feeling better about it now but looking forward to getting it to a frame builder to see how they will fix it and how strong it will be afterwards - hope it won't remin a weak spot.

Any ideas what might have caused it? I wondered about strain from the seatpost. I have about 10mm of seatpost in the tube which takes it well past the top tube and its below the minimum insertion mark - is this enough? Also wondered if it could be from over-tightening the seat clamp - it does seem to need to be done pretty tight to prevnt the post from slipping.

Thanks,

Ross

Naugas · May 16, 2010

10mm should be 100mm I guess? Maybe the seatpost needs to be even longer. It looks like it has cracked simply because of too much strain. How long is the protruding part of the seat tube?

kaiser · May 16, 2010

Could just be wear and tear or a weak spot from the start.

suburbanreuben · May 16, 2010

It's not the tidiest looking weld in the world, TBH; I think it has just been weak from the start. What bike is it?

the great roberto · May 16, 2010

suburbanreuben":2oyc87cx said:
It's not the tidiest looking weld in the world, TBH; I think it has just been weak from the start. What bike is it?

Agree.Tidy does it too much justice.

I would have thought a run with a TIG torch should solve teh issue.Make sure both sides are clean and free of rust etc. May be worth running the torch over the original weld as well.
Post weld (and when cold !) see if you can dye penetrant test the defect to see if it is "indication " free.i.e fixed !

renaldo · May 16, 2010

I did mean 10cm rather than 10mm for how far the seat post inserts

current seat post is 300mm long and looking a bit tatty so might look into getting a longer one to help reduce strain in the future, and look into getting a collar which its never had. The seat tube extends for about 45mm above the top tube which seems quite a lot without any support.
The bike is a 98 (I think) Sunn and hasn't had a particularly tough life as I'm not the most rough or extreme rider by any stretch of the imagination. I don't know what their reputation is like for durability or workmanship but would be interested in anyone else's experiences.

Seat tube crack - advice wanted

renaldo

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