Originally Posted by
ksisler
FB; 100% agree on causal assessment. The root cause of that is usually a frame that is a few inches too small, leaving the rider to jack up the seatpost which is then coupling with the design that has the extended seat tube as you mentioned. The crack is predictable.
- To fix the frame well enough to ride, I would want to ask my local welder (a TIG qualified one) to run a weld right through the middle of the crack and a big beyond the ends. It would be smart to take out the seat post before welding (hah) and it may be necessary to run a seat tube reamer afterwards. If desired, one could file down the weld bead afterwards and spit a bit paint on it.
Would be putting in an extra long post after the repair, but I always try to use an extra long seat post even on a steel frame.
In a standard double-diamond frame, esp. one with an extended seat tube rising above the seat stays and top tube, not having enough post inserted is almost always the cause as any force int he seatpost is transferred directly to the top of the seat tube juction. Hoever, the OP's frame was most certainly NOT a double diamond frame (no seat-stays, very short distance between the top welded joint ont he seat tube and bottom welded joint on the seat tube... no matter how much seatpost was inserted into the frame, every bit of force on the saddle was resisted by the joints between the top tube/'down-tube' (for lack of a better name) and the seat tube. The OP said he cut an inch off his seatpost to get it to fit, which indicates he had less than the maximum height you would normally have with a full length seatpost, and likely the remainder of the post was damn near the bottom of the interrupted seat tube.
No matter, he has since retired that frame, anyways.