Bulgecrack on seat tube - how dangerous?
05-27-22, 02:17 AM
#1
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Bulgecrack on seat tube - how dangerous?
Hello all!
I will start working on my Crescent branded Motobecane (I believe Team Champion).
It has a crack-bulge beneath the seat tube slot. The crack (or maybe slot cut too long??) goes straight down, on the inside I can feel a shallow longish bulge to the outside.
I think the frame is not suitable for all-out hard cycling, but quite safe for casual riding, no?
The things I am not sure:
- could it be a manufacturing fault- the slot cut too long? (the relieve hole is not in center, but probably unrelated)
- another possibility: water freezed in the seat post flute and caused bulge (the seat post is not fluted, but I am not sure if it is original).
- will extra long seat post help to distribute stresses more evenly?
I will start working on my Crescent branded Motobecane (I believe Team Champion).
It has a crack-bulge beneath the seat tube slot. The crack (or maybe slot cut too long??) goes straight down, on the inside I can feel a shallow longish bulge to the outside.
I think the frame is not suitable for all-out hard cycling, but quite safe for casual riding, no?
The things I am not sure:
- could it be a manufacturing fault- the slot cut too long? (the relieve hole is not in center, but probably unrelated)
- another possibility: water freezed in the seat post flute and caused bulge (the seat post is not fluted, but I am not sure if it is original).
- will extra long seat post help to distribute stresses more evenly?
05-27-22, 02:39 AM
#2
blahblahblah chrome moly
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Ride it and be happy. There's a good chance the crack will not go anywhere. Sometimes cracks like that propagate until they get into less-stressed metal and then propagation stops and it can stay like that essentially forever. The way to find out is to ride it and see.
Repairing it is difficult and would ruin the paint, and this frame might not be worth such a Big Hairy Deal repair. Probably would mean replacing the seat tube. Should it eventually need a repair, and should you decide to go for it, riding it now will not make the eventual repair harder, so you have nothing to lose.
Just be glad you don't have a bulgie crack, those are nasty!
The artifact I'm seeing on the inside looks like maybe a seatpost was frozen and they sawed through it with a hacksaw and went a little too far? (aka a "hack job") Just a guess.
Mark B
Repairing it is difficult and would ruin the paint, and this frame might not be worth such a Big Hairy Deal repair. Probably would mean replacing the seat tube. Should it eventually need a repair, and should you decide to go for it, riding it now will not make the eventual repair harder, so you have nothing to lose.
Just be glad you don't have a bulgie crack, those are nasty!
The artifact I'm seeing on the inside looks like maybe a seatpost was frozen and they sawed through it with a hacksaw and went a little too far? (aka a "hack job") Just a guess.
Mark B
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05-27-22, 03:34 AM
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Hone or very good careful cleanup, grease, plenty long proper diameter seatpost and it may go forever. 
05-27-22, 05:04 AM
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Thankfully your first two replies to this thread were from credible posters that didn't offer alarmist viewpoints. I'd ride it and if it bothered me, I would check it periodically.
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05-27-22, 06:25 AM
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That crack/bludge is, most likely a product of a seat post that was not inserted far enough into the seat tube. If the next seat post installation is not deep enough, expect the crack to get worse. If the post goes below the crack, you might be OK but don't hold me to that. Also, were I you, I would drill a small hole at the blind end of the crack to help prevent it from running further.
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05-27-22, 08:38 AM
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05-27-22, 09:19 AM
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I'd probably try to make sure that I have an overly long seatpost that goes well below that point (likely caused by an under-inserted post) and look at the crack from time to time but keep riding it.
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