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Dented/crushed top tube on a triple-butted frame by a child seat. Repairable?

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Dented/crushed top tube on a triple-butted frame by a child seat. Repairable?

Old 10-20-20, 12:09 PM
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Dented/crushed top tube on a triple-butted frame by a child seat. Repairable?

I was sent here from the Bicycle Mechanics thread so I wonder if you would have any qualms over repairing the following situation with frame blocks (See here for an example)?
The frame seems to be flattened by the child seat, a Zadel op stang No. 5, which is perfectly fine for straight gauge gas pipe tubing as is common on Dutch city bikes but not on lightweight touring tubing... as can be seen here.

Let's say we can get this perfectly round again, anything I should look for?

Originally Posted by JaccoW
So I came across one of my dream bikes, in my (rare) size (66cm / 26 in.), for cheap (€30 / $35), but... somebody mounted a child seat on the middle of the frame somewhere in the past and seriously dented the frame.

It's a 1993 Koga-Miyata WorldTraveller, the Dutch market version of the Miyata 1000 that was more common in the US. They came with oversized triple butted chromoly tubing on the frame, unicrown forks and all the cool stuff you would want on a vintage tourer.
Would this be repairable? I think you could go a long way with frame blocks but most likely this would need some attention from a frame builder.

I would love the technical challenge of this but is it safe? Or can you only tell when you've already put some time and effort in it?

Pics:




P.s. I know the size would be good for me but I seem to pick out mistreated big frames some times.

Last edited by JaccoW; 10-20-20 at 12:40 PM.
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Old 10-20-20, 06:00 PM
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Hard to say from here. I can imagine that it might be crushed badly enough to not be fixable by rolling
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Old 10-20-20, 07:15 PM
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I have two comments- First is that I don't think this damage is of any great concern, as long as that child seat is removed. (As in the loading that wasn't designed into the frame is stopped). Sure a repair could be tried, rolling the tube in blocks likely will reduce the ovalness. But paint damage and a less then fully round result is to be expected.

Second is this is one more reason to dislike this type of child carrier. IMO this position is akin to having you child sit in front of you when in a car... Andy

Extra credit- That seat's clamp is a great example of how cheap a product can be made.
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Old 10-21-20, 02:21 AM
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Originally Posted by unterhausen
Hard to say from here. I can imagine that it might be crushed badly enough to not be fixable by rolling
Yeah I'm going in for a closer look. For €30 it's a fun look at a bike like this and will show me what to look for in another example. And who knows, I might be able to fix it.

Originally Posted by Andrew R Stewart
I have two comments- First is that I don't think this damage is of any great concern, as long as that child seat is removed. (As in the loading that wasn't designed into the frame is stopped). Sure a repair could be tried, rolling the tube in blocks likely will reduce the ovalness. But paint damage and a less then fully round result is to be expected.

Second is this is one more reason to dislike this type of child carrier. IMO this position is akin to having you child sit in front of you when in a car... Andy

Extra credit- That seat's clamp is a great example of how cheap a product can be made.
From what I understand the big advantage of a seat like this is that you can carry older children in the middle of the frame. Once they get too big (6-8 years) a rear or front carrier won't work anymore.
But there's a reason why they are not that common anymore nowadays.

First thing I plan to do is remove the seat and assess the damage. Chances are the paint is already damaged by the carrier. Those frame blocks aren't terribly expensive fortunately. If it can be fixed I plan on making it a rider, not a museum piece. Besides, I don't care too much for the original paint here, even if it was pristine. It's on the wrong side of 90's gaudiness for me.
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Old 10-21-20, 05:37 AM
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In addition to being squashed by the clamp, it appears that the tube is bowed/bent down as well. It will probably never be perfectly straight or round again, but it will be fine to ride.
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Old 10-21-20, 11:41 AM
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I have never used one of those carriers, but they seem fine in the pictures I have seen of them being used. And as the OP said, they make bikes with really stout tubes for jobs like that. I have a Batavus frame that is just incredibly stout.

For 30 euro, I think I would chance it. Not likely to crack, unless they pierced the tube.
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Old 10-23-20, 01:51 PM
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Got the frame today and it looks like this might be salvagable. The dent is hardly visible without the child carrier but there is some bulging when checked with a caliper.
Made a project thread in the C&V section for those wanting to see more pictures and how the un-denting goes in the future.

Thank you all for your input.


Slightly dented on top


Barely dented below


29mm tube in the rear


31mm around the dent


27 up down around the dent


Spider underneath


But all in all a great basis for a project.
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Old 10-23-20, 06:20 PM
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Looks nice, great that they didn't crush it too badly. Are you going to get a dyno for that lever?
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Old 10-24-20, 03:43 AM
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Originally Posted by unterhausen
Looks nice, great that they didn't crush it too badly. Are you going to get a dyno for that lever?
Personally I prefer hub dynamos but I will try to get the original working first. For now I think it needs a good clean and maybe a good look at the springs. It moves but just barely.
I do wonder what would be a good alternative thing to do with it though.

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