Top of seat tube bent
#1
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Top of seat tube bent
Hi there,
I'm doing a basic clean and tune up of a trek 800 sport. My neighbor let me have it and I think it will make a decent utility bike for my wife. The seat post was stuck but eventually came loose with oil and twisting. However, it looks like the previous owner had unsuccessfully tried to get it out by bending out the very end of the seat tube that extends above the brazed on seatpost collar. In other words, I can clamp on the seat post no problem, but the sharp and pointy ends of the top of the seat tube are slightly flared out. Any suggestions about how to bend these back in? It's not very visually pleasing, plus I'm worried it might lead to a physical injury. Thanks.
ps: I tried uploading pics to illustrate my point, but the site tells me can't until I have 10 posts. Is there a workaround?
I'm doing a basic clean and tune up of a trek 800 sport. My neighbor let me have it and I think it will make a decent utility bike for my wife. The seat post was stuck but eventually came loose with oil and twisting. However, it looks like the previous owner had unsuccessfully tried to get it out by bending out the very end of the seat tube that extends above the brazed on seatpost collar. In other words, I can clamp on the seat post no problem, but the sharp and pointy ends of the top of the seat tube are slightly flared out. Any suggestions about how to bend these back in? It's not very visually pleasing, plus I'm worried it might lead to a physical injury. Thanks.
ps: I tried uploading pics to illustrate my point, but the site tells me can't until I have 10 posts. Is there a workaround?
Last edited by friasc; 10-02-20 at 12:26 PM.
#2
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Never Fix A Running Piece. You could file off the sharp corners to avoid the (remote, IMO) chance of injury. You could also try removing the post and tapping the ears in (one of the very few times I would put a hammer to a bike!) but you run the risk of distorting the tube to the point where it might be difficult to get the post back in. If you leave the post in you will never get them flush but might get close.
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We use a junked seat post in the tube while carefully tapping the ends in with a hammer. The old seat post acts as a shaping mold and helps prevent accidently distorting the tube.
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From the sounds of things I would worry about pinching a finger on such a flare.
I like JoeTBM's idea, some sort of hammer and dolly. Light taps only.
I like JoeTBM's idea, some sort of hammer and dolly. Light taps only.
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#5
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Thanks for all the answers. I just realized that the problem is worse than I thought. I can only fit the seat post a few inches inside the seat tube, then it gets more and more stuck as it comes into contact with the seat tube. I tried shoving it in a bit and I could see some aluminum grinds forming at the very top of the seat tube (it already got heavily gouged when I first removed it, so I wasn't too worried about scratching it a bit more). My guess is that by deforming the 'ears' of the seat tube in an attempt to unfreeze the seat post, the previous owner ended up 'ovalizing' the opening. As the seat post does deeper into the seat tube, it eventually comes into contact with the narrowest diameter of the seat tube opening (I hope that makes sense). In any case, the problem is not as cosmetic as I initially thought.
Given the modest intentions I have for this bike, what is the path of least resistance here? Should I get a slightly smaller seat post (the sticker on the factory original seat post says 26.6mm)? Should I take it to the bike shop and see if they can reshape (might be very expensive for such a lowly old bike)? Should I just ram the seat post into the right height and never change it?
I thought about following one of the suggestion previously posted and gradually tapping in a seat post, but unless it's a seat post made of steel, like the frame, won't it just grind down against the seat tube, rather than altering its shape?
Given the modest intentions I have for this bike, what is the path of least resistance here? Should I get a slightly smaller seat post (the sticker on the factory original seat post says 26.6mm)? Should I take it to the bike shop and see if they can reshape (might be very expensive for such a lowly old bike)? Should I just ram the seat post into the right height and never change it?
I thought about following one of the suggestion previously posted and gradually tapping in a seat post, but unless it's a seat post made of steel, like the frame, won't it just grind down against the seat tube, rather than altering its shape?
Last edited by friasc; 10-20-20 at 02:16 PM.
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#7
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There are two common ways to damage a seat lug. One is to use an undersized post and force the lug ears inward in hopes of getting it tight. The other is to have the seat very high with inadequate post inserted into frame. Then the riders weight shoves the lug and tube backwards.
Then there are the consequences of hamhanded efforts to fix the above. All of this is very very very common.
Try to figure out how the bike was damaged. Be very certain you are using correct original sized post. Do not attempt to compensate for past damage by using an odd size post.
It is a steel bike and this is a common enough repair. If bending metal is not something you are familiar with or comfortable with take this one to a mechanic.
Then there are the consequences of hamhanded efforts to fix the above. All of this is very very very common.
Try to figure out how the bike was damaged. Be very certain you are using correct original sized post. Do not attempt to compensate for past damage by using an odd size post.
It is a steel bike and this is a common enough repair. If bending metal is not something you are familiar with or comfortable with take this one to a mechanic.
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Maybe the seatpost is bent, and there is nothing wrong with the frame?
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OK so I found a steel pipe section with an outer diameter of 1.05 inches, which is just 1 mm greater than that of the seat post (26.7 mm vs 26.6 mm). After tapping it in a few inches and removing it, the seat post slides right in no problem. I also managed to bend the ears back in a little. For me, the problem is resolved at this point. Thanks for all the input everyone
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No, the rest of the frame is almost impeccable, its just the very top of the seat tube that is (was) a bit bent out of shape