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Crimping 753 chainstays

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Crimping 753 chainstays

Old 04-12-21, 02:20 PM
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gilmo789
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Crimping 753 chainstays

Hi,
I procured an interesting frame from ebay. It's 753 by Keith Laker (no idea) but made for old 27" wheels which means there's tons of clearance for tyre height. The perennial problem with old frames however is the width of the chain stays. 30c tyres just fit but I'd like a smidge more clearance if possible. I've crimped the stays of other frames like 531 or Aelle without issue and I'm not precious about the paint but people seem terrified of 753 so I thought I'd ask if anyone's done it.

I don't think a small dent would be a huge problem: See table herein:
(I'm not allowed to link to forums, you can find the table by googleing '753 ductility and clicking on the 'road bike review' thread, post by 'scooper' p2)

Ductility (% elongation) of the more exotic steels is 8% whereas the 'lesser' steels is 10%. If 10% lets you put in a big dent then surely 8% would allow for a wee dent, no?

thoughts?
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Old 04-12-21, 06:11 PM
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I swear there was a recent thread about this and the consensus of the people that have worked with 753 was that it wasn't a good idea. It's heat treated not so exotic steel, which means the force required to dimple is higher. I have not had good success bending heat treated steel tubes, but that's not quite the same thing. Denting it was part of the lack of success.

In general, you can damage a chain stay by dimpling it. And it also may break later.
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Old 04-12-21, 06:16 PM
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Are you talking about this info sheet?
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Old 04-12-21, 08:30 PM
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Given the history of chainstay cracks at the crimps the 753 ones reportedly suffer from don't do it. My memory says that Reynolds subbed 531 stays and blades early on after the initial introduction of 753 because of this brittleness. Andy
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Old 04-13-21, 05:09 AM
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thanks for the replies


I infer that the the heat treatment makes the steel brittle, like tempering. I'm just wondering why, from a metalurgical point of view, 753 is so fragile.

Internetting tells me that elongation of 7075 alloy is 11%, 4130 steel is 25% and 531 is 10%

Is this even the correct measurement when discussing how much deformation you can safely apply to a tube?
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Old 04-13-21, 07:05 AM
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Originally Posted by gilmo789 View Post
I infer that the the heat treatment makes the steel brittle, like tempering.
Not quite; tempering means to try to get some toughness back after the quench leaves the steel in a hard but brittle state. Tempering weakens the steel but if done right leaves the steel still stronger than it was before the whole quenched-and-tempered heat treating. The process has many variables they play with to get the properties they want. 753 almost certainly changed the particulars of its heat-treatment over the years, so you probably can't say anything categorically true for all 753.
Internetting tells me that elongation of 7075 alloy is 11%, 4130 steel is 25% and 531 is 10%
I would say those elongation numbers are wrong, because not enough information is given for them to be really right. It depends a lot on the exact metallurgy, which can vary hugely within those categories. Say sticking within 4130, between annealed on one end, and quenched (not tempered) at the other extreme, you'd see a vast range of elongation numbers. Add in the effects of cold-working on top of the heat-treat factors, it gets complicated. I'm not saying I understand it!

Is this even the correct measurement when discussing how much deformation you can safely apply to a tube?
Not exactly, though it is a good one to look at. But the real limits to what you can get away with there depend on other factors too, like the diameter-to-wall ratio, which when it's high leads to catastrophic crumpling failure. Imagine trying to put a smooth curve in a beer can, with no localized kinking. You may also need to deal with the rate at which the metal work-hardens as you indent it.

Jim Merz, who made more 753 frames than most anyone (in the US anyway, not counting Trek), told me you'd need to soften the steel in the vicinity of the indent. Sorry if I'm mis-remembering what he said, and I don't know if he said he actually tried that, or if he was conjecturing. Sounds do-able to me though, if you won't be too sad if it fails, and/or if the frame is worthless to you without the increased tire clearance. Heating it to roughly the silver-brazing temperature range and holding it there a while would temper it more, trading a loss of strength for more ductility. Heating it to red hot, roughly brass brazing temperature, then letting it cool naturally in room temperature still air, would result in "normalized" steel, which contrary to popular belief is actually a pretty decent combo of strength and ductility in these low-alloy steels. It is essentially turning 753 into 531 "as-delivered", though maybe with a bit less strength than 531 due to 531 having cold-work done to it after normalizing. Also there would be a relatively soft tempered zone around the fringes of the part you got red-hot. Counter-intuitive, but the part that only got to silver temperature. That over-tempered area will be the weakest part of the tube, more like the strength of 531 after brazing, which is weaker than as-delivered. Having that weak tempered zone of the HAZ can be OK if it falls out past any "features" like changes in thickness, such as you find at the end of a lug point, a bad place to put the weakest part of the HAZ. For example if there's a chainstay bridge near where you heated the stay to soften it, that discontinuity will likely be a stress-riser that will cause it to fatigue crack there. With such thin tubing, and not particularly strong compared to modern super-steels, fatigue is likely to end up being the frame's cause of death eventually.

Think hard about the shape of your indent also; there's a right way and a wrong way! In my opinion, you can't do much better than the indent that older Columbus SL/SP used, sort of a leaf or boat shape, with a fairly sharp crease down the middle. Normally we avoid sharp creases but in this case the sharp crease down the middle doesn't cause problems, and it leaves the steel in a pretty mellow shape bending-wise, elsewhere where it does matter. Many nice old bikes with indents like that survive from 70, 80 or more years ago. Look at the indents in a Barra aluminum, shaped like the SL indent, and Barras aren't known for breaking there. (They break, but somewhere else!) About the worst you can do is a transverse indent such as you get by hammering a pipe against the stay. A flat spot is pretty bad too Reynolds tried that with the original shape of their 531 SL chainstays, many of which broke. Later 531SL with the round-oval-round chainstays are more reliable.

Let us know if you try it, how it turned out. A lot of people with 753 frames want to know the answer to your question. I indented a ton of Tange Prestige stays, a similar quenched-and-tempered low-alloy steel, but Prestige had a softer heat-treat (more tempered) than 753. I suspect Prestige chainstays may have been even softer than the main triangle, specifically to allow the builder to manipulate the shape.

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Old 04-13-21, 11:31 AM
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There was a problem with 753 chain stays breaking when it 1st came out. I had 2 Raleigh frames come through my frame shop that had cracked chain stays. That scared me off of getting my 753 certification and I still have a check for 75 in my desk made out to Reynolds to pay for a 753 test tube kit. I never sent it in after seeing those cracked stays. A frame I made with cracked tubes could be very expensive in money and time to fix (bicycle tear down and rebuild, replace chain stays and repaint) and my reputation could take a huge hit even though it wouldn't have been my fault (and then the customer might still insist on a new frame anyway). At 1st Reynolds required you send them a complete frame for testing. When I talked to Terry Bill in Birmingham at their factory in 77 or 78 (I don't remember exactly), he said every American up to that point had failed their test. Jim Merz was the 1st and Rich Gangl the 2nd American builders to pass the test. Right about then, Tange came out with their Prestige line that mimicked 753 so I used that instead for my light frame builds. Later when Reynolds revised the test to be easier, I applied and got my 753 certification. I understood by then they had fixed the chain stay problem with added material and probably less treatment.

Because your frame is made for 27 1/4" rims, I would be suspicious it was early in the era when 753 frames were made and therefore more likely to be before they altered 753 chain stays to keep them from breaking. With my history of 753, I certainly wouldn't take the chance of trying to indent the chain stays. There isn't that much difference between a 30mm tire and a 32. You don't notice the difference as much in back as the front anyway. Besides we are frame builders that can make modern wide tires fit the frames we build.

My understanding of Columbus Aelle tubing was that it was not heat treated like SL or SP. I don't know if it was a different alloy. This you can see in the surface of both kinds of tubes. The SP/SL tubing has a bluish/golden hue while Aelle is plain gray. I remember looking at a video of Columbus SL tubing being made at the Columbus booth at the bike show in New York in the 70's and they showed a black screen with the words "secret progress" - which I assumed later was their heat treatment process. My point is that Aelle tubing would probably be more ductile and more likely crimp with success.
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Old 04-13-21, 02:23 PM
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Thanks for the responses guys.

I haven't any idea how old the frame set is, but some of the components are quite old, like a fluted shimano 600 crank and an old campag headset, but the decal looks like a more modern vinyl type and has purple lettering which makes me think its not that old. Anyay it's clearly been used a lot and the chainstays haven't cracked yet. there's no shainstay bridge either. It doen't seem like a very old bike. I think it was probably a custom job.
Another weird thing is that the rear wheel sits slightly off centre but the spacing is 126; so the rear triangle has been bent at some point.

89-94 style decal
ww.reynoldstechnology.biz/wp-content/uploads/2015/10/decal_history.pdf
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Old 04-13-21, 03:40 PM
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Originally Posted by gilmo789 View Post
Thanks for the responses guys.

I haven't any idea how old the frame set is, but some of the components are quite old, like a fluted shimano 600 crank and an old campag headset, but the decal looks like a more modern vinyl type and has purple lettering which makes me think its not that old. Anyay it's clearly been used a lot and the chainstays haven't cracked yet. there's no shainstay bridge either. It doen't seem like a very old bike. I think it was probably a custom job.
Another weird thing is that the rear wheel sits slightly off centre but the spacing is 126; so the rear triangle has been bent at some point.

89-94 style decal
ww.reynoldstechnology.biz/wp-content/uploads/2015/10/decal_history.pdf
I'd be surprised if anyone built frames around 27" wheels after the 70's but it is possible. Any dent in a heat treated tube creates the possibility of cracking where the dent is located. I've seen this happen on small dents in seat and down tubes. All I can say is that I would never try to dent a heat treated chain stay if it was my own bike. If somebody paid me and damn any consequences, I would try to increase the ovalization using 2 pieces of flat wood that are shaped a bit like the stay so there is no edge that might indent the stay. I would not use any of the shapes commonly used today to try and increase clearance that create an indent like a crater. Wherever there is a crease greatly increases the chance of cracking.

Many frames are built out of true. This is especially the case that one rear stay is just a bit longer than the other. This is one of the hardest things to get right when building a frame. That mismatched distance is amplified out by the rim/tire by a factor of almost 3. In other words if one seat stay is 1mm longer than the other, than the tire will sit over almost 3mm from center. Of course it is also possible that the dropouts are not equidistance from the frame's centerline. This can be especially true for small time builders that don't have good fixturing or alignment tables.
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Old 04-16-21, 05:58 PM
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Originally Posted by bulgie View Post
Heating it to roughly the silver-brazing temperature range and holding it there a while would temper it more, trading a loss of strength for more ductility. Heating it to red hot, roughly brass brazing temperature, then letting it cool naturally in room temperature still air, would result in "normalized" steel, which contrary to popular belief is actually a pretty decent combo of strength and ductility in these low-alloy steels. It is essentially turning 753 into 531 "as-delivered", though maybe with a bit less strength than 531 due to 531 having cold-work done to it after normalizing. Also there would be a relatively soft tempered zone around the fringes of the part you got red-hot. Counter-intuitive, but the part that only got to silver temperature. That over-tempered area will be the weakest part of the tube, more like the strength of 531 after brazing, which is weaker than as-delivered.
Tempted to give this a go...
How long would I have to hold it (cherry red?)?
should I do the whole circumference of the tube or just the bit i want to dent?
All I have is MAPP - is that hot enough?
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Old 04-17-21, 03:54 PM
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Originally Posted by gilmo789 View Post
Tempted to give this a go...
How long would I have to hold it (cherry red?)?
should I do the whole circumference of the tube or just the bit i want to dent?
All I have is MAPP - is that hot enough?
Sorry about the slow response, I missed your question.

I haven't done this exact procedure, closest I have done is softening the stay tip to allow shaping for the freewheel/chain clearance on the inside of the right dropout. That's a safer place to be messing with the heat treatment.

The tire clearance point on the chainstays is harder to get evenly hot, but a oxy/Mapp torch would be a good choice. If you only have an air torch (no oxygen), I wouldn't expect that to be hot enough, but I haven't tried it.

You want a very smooth general heat without hot/cold spots, so a large soft flame is best, and keep it moving. Heating one side of the tube will cause it to curve ("witch wanding"), so go for even heat all around. I expect better results with a dummy axle installed but maybe it's better to let the parts move however they want? Opinions please.

I'm not an expert on this but I think it only needs to come to red heat more or less for an instant, for thin wall tubing. You can assume that the temperature you see on the outside is the same all the way through, unlike with a thick part. Maybe there is some slight delay while the metal ions rearrange themselves into the high temperature stable crystal lattice, essentially erasing the prior heat treatment. Someone here will probably know. But my understanding is that once you get it red, you're done. Cooling needs to be slow but not too slow. Normalized is a stronger state than annealed, which is what you get when you make it cool very slowly in an oven. For thin wall tube, cooling naturally in still, room-temperature air is solidly in the range of Normalizing -- neither annealed nor quenched.

There is some self-quench when you only heat part of a tube, where heat is sucked away from the hot part by conduction to the cold part of the tube. This is unavoidable to some extent, but probably you can mitigate it by heating a larger area to a temperature below the tempering range. My gut feeling is that it's not a huge concern. I'd be more worried about the over-tempered part of the HAZ, just past the part that got red hot. That'll be the weakest point, so try to keep it away from lug edges or the chainstay bridge. In fact if there's a bridge, I might be inclined to remove it. It's more likely to cause a fatigue crack than it is to prevent one by any "reinforcing" effect. The larger the HAZ, the larger and softer the over-tempered area will be, so that would indicate working fast and not heating more of the tube than necessary.

On a short-chainstay racing bike (very likely, on a 753 frame), you won't have much room between the tire clearance point and the BB shell lug points, so you are in danger of having the weakest part of the HAZ right there at the stress riser of the lug point. Thinning the points to feather into the tube reduces the thickness discontinuity, probably worth it for improving the fatigue endurance.

Mark B

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Old 04-17-21, 09:45 PM
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gilmo, how much experience do you have using any kind of brazing torch? I ask because I've taught hundreds of people how to braze. Most beginners have certain patterns they have to overcome in order to be successful. One of those traits is not having a sense how to move the flame evenly over a specific area. I'll use an example to explain the problem. If one is painting a wall with several coats of paint, they need to do so without missing some areas and putting 5 coats on another. And they shouldn't be putting paint on the floor and ceiling. Add to that a common tendency to not keep the flame at the same distance to the work. Sometimes a student's flame almost touches the metal and sometimes it is too far away. In addition their movements tend to get locked into a specific pattern (where they retrace a pattern) when they move back and forth instead of getting even coverage.

Now add to this problem, it is challenging to access all parts of the frame with your flame without difficulty. Something gets in the way. This means you have to think how you hold the frame in like something like a Park stand so you can move around it easily at a comfortable height (I suggest having the chain stays pointing straight up). The concept of heating the area is not complicated. What I'm telling you is that from my experience it will probably be more challenging than you might think.

My advice of course would be not to do it on a 753 frame but I'd be willing to bet you won't take my advice and do it anyway. In that case I recommend practicing with some throw away frame before you damage a good one. You will learn a lot during your practice run and see what you might need to change when you do it for real. Of course cheap frames have heavy tubing that take a lot more heat before they get up to temperature. Thin wall tubing will heat up amazingly fast and require better torch control. it is really easy to go from a proper cherry red color to orange or nearly white and do some real damage.

I've seen some ugly dents trying to create more clearance. Andy Stewart made a very nice tool to indent a chain stay for more clearance. You may have already figured out a good way to dent stays but you might want to ask Andy to send you a picture of his cool tool in case his is better.

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Old 04-18-21, 04:51 AM
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Originally Posted by Doug Fattic View Post
gilmo, how much experience do you have using any kind of brazing torch? I ask because I've taught hundreds of people how to braze. Most beginners have certain patterns they have to overcome in order to be successful. One of those traits is not having a sense how to move the flame evenly over a specific area. I'll use an example to explain the problem. If one is painting a wall with several coats of paint, they need to do so without missing some areas and putting 5 coats on another. And they shouldn't be putting paint on the floor and ceiling. Add to that a common tendency to not keep the flame at the same distance to the work. Sometimes a student's flame almost touches the metal and sometimes it is too far away. In addition their movements tend to get locked into a specific pattern (where they retrace a pattern) when they move back and forth instead of getting even coverage.


Now add to this problem, it is challenging to access all parts of the frame with your flame without difficulty. Something gets in the way. This means you have to think how you hold the frame in like something like a Park stand so you can move around it easily at a comfortable height (I suggest having the chain stays pointing straight up). The concept of heating the area is not complicated. What I'm telling you is that from my experience it will probably be more challenging than you might think.


My advice of course would be not to do it on a 753 frame but I'd be willing to bet you won't take my advice and do it anyway. In that case I recommend practicing with some throw away frame before you damage a good one. You will learn a lot during your practice run and see what you might need to change when you do it for real. Of course cheap frames have heavy tubing that take a lot more heat before they get up to temperature. Thin wall tubing will heat up amazingly fast and require better torch control. it is really easy to go from a proper cherry red color to orange or nearly white and do some real damage.


I've seen some ugly dents trying to create more clearance. Andy Stewart made a very nice tool to indent a chain stay for more clearance. You may have already figured out a good way to dent stays but you might want to ask Andy to send you a picture of his cool tool in case his is better.

Hi,

The short answer is not a lot, but I am fairly mechanically competent and I know how to move the torch around. I think, at the moment, i'm unwiling to do it because all I have is a Bernzomatic MAPP torch so I dont know that I can get enough heat in it, and the flame is a bit unweildy.


bulgie Thanks for that. Fortunately the frame has loads of clearance to the bottom bracket and ~53mm drop at the rear brake. I think it must have been built for someone who had a stock of narrow 27" tyres and nice wheels. the clearances don't make sense otherwise considering there are no muguard eyes. I'd post a few photos but I am not allowed...
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Old 04-18-21, 05:05 AM
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Rather than running the risk of cracking the chainstays, perhaps you should consider installing 650b wheels and tires, as many people have done who wanted to run wider tires in a frame built for 700c or 27" wheels.
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Old 04-18-21, 09:25 AM
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Originally Posted by gilmo789 View Post
The short answer is not a lot, but I am fairly mechanically competent and I know how to move the torch around. I think, at the moment, i'm unwiling to do it because all I have is a Bernzomatic MAPP torch so I dont know that I can get enough heat in it, and the flame is a bit unweildy..
My long winded response could be boiled down to Practice 1st if you are determined to try it. If I was going to anneal some part of a good frame, I would definitely practice 1st. And I have more years of brazing experience than many posters have been alive. I've got tons of different torches and tips (to help students find their preferences) but probably I would choose one of my rosebuds (they come in different sizes). A rosebud has multiple flame holes that provides a greater volume of heat. They can be used with either acetylene or propane. This allows you to hold the flame further back covering a wider area without the need to dance the flame around trying to get even heating (the problem I mentioned in my previous post). In other words a big soft flame is easier to control then a small hot one. I don't have any experience to know if a mapp gas hand held torch has enough power to work well. You won't be sorry making the extra effort to do a practice. You might be sorry just going for it hoping for the best.
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Old 04-18-21, 04:04 PM
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gilmo- If you are near me I will offer some tool loans or help. Location in your bio helps us to guide you better. Andy
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Old 04-19-21, 02:04 AM
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Originally Posted by Andrew R Stewart View Post
gilmo- If you are near me I will offer some tool loans or help. Location in your bio helps us to guide you better. Andy
That is very kind, but I am in Scotland...
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Old 04-19-21, 08:22 AM
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Originally Posted by gilmo789 View Post
That is very kind, but I am in Scotland...
In that case maybe Andy can send you a picture of his chain indenting tool. Its pretty cool. If you already have a decent set up, others could benefit from seeing how Andy does it.
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Old 04-19-21, 08:25 AM
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I would definitely like to see it
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Old 04-19-21, 08:25 PM
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Ask and you shall see Here's three different crimping methods/tools. The bench vise method was the first way I did this. (The wood block is one half of the stay ovalizing blocks I hand filed a long time ago). The challenge to better hold the stay in place drove me to the steel block method. Fine if the stay is not attached to the shell. But it lacks clearance for a prebuilt bike so the erector set design is what I then made. I do like this one for a few reasons, one being that it needs no mill or lathe or precision tooling to make. Note the alignment steady "tail" running along the stay's length. This tool can be broken down and used with only two layers if needed too.


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Old 04-20-21, 03:22 AM
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That is glorious, what is it made from?



While we're on the on the subject of denting 753 chainstays, has anyone any opinions on accidental damage?

I have a 708 frame which apparently has a 753 rear triangle. I was running it as a single on a double crank with the chainring on the outside. The chain came off, wrapped around the inside of the crank spider arms and when it came up past the chainstay it gouged out a small sliver of metal and made a small dent. There were no cracks and I filed it very gently so there are no obvious stress risers. Hasn't broken yet; any thoughts on this damage?
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Old 04-20-21, 09:06 AM
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The erector set style of crimping tool is made of plate steel, hand filed/ground steel form and all thread rods with other bits that should be obvious. The plate is about 3/8" thick, I went to a local steel supplier and sorted through their scrap for it. The all thread and other bits were local hardware store stuff. The form is held onto the plate with machine screws.

I've seen dozens of production bikes with chain suck damage as you describe. None that I can remember have produced cracks including many Al frames. But 753 is somewhat more brittle then other materials so I don't know the future reliability of your 753 stays. My initial thoughts about "fixing" this are to patch the damaged spot with a thin and well curved plate, silver brazed on. But this will make ring clearance more problematic so some home work is advised WRT clearance. One could fill the dents with brass but this would only be a cosmetic solution, IMO. If this were my bike (and I have done the same chain suck damage to a tandem I have) I would just ride it and monitor periodically for more problems (and I would replace worn rings/chain as keeping them in good condition is a big way to avoid future chain suck just as always soft pedaling is the technique solution too). Andy
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