Hi, fellas. I recently purchased a pre-owned Dahon Impulse D7 in Beijing at a nice price. Having shipped it to my residence, I found that overall the bike was in a good condition. However, after further scrutiny, there are some problems with the bike tho. And I would like to hear professional advice from all of you, as this is my first Crmo frame bike. I really want to treat it right. Thanks in advance for any advice!

First. there is a needle-sized spot of rust on the seat tube, which looks quite deep and doesn't look like a surface rust to me.

Second, an area of rust is found inside the steel frame when peeking thru the holes of the main tube. I have no clue whether this only surface rust or harmful ones. (Zoom in and you'll find something shimmering inside the tube. Creepy)

Is it necessary for me to find a bike mechanic shop to have it repaired and refurbished? I was told that the whole service would only cost me 218 CNY. ( equivalent to $30).
If not, what should be done and what can be done by myself?
Is there anything that I could apply to prevent it from rusting? (Boeshield T-9 isn’t sold in China, so buying it here would cost me an arm and a leg.)

Any suggestion is appreciated!!!

Steel is a wonderful metal (alloy actually) in that rust grows fairly slow but is easy to slow further. I see no real concerns, based on the photos. But that's likely not what the OP is thinking...

What would I do? Hight road or low and little? Low and little is to spray inside the tubes some sort of protectant (like Frame Saver or even WD40) and clean off the external rust spots then dab on some sort of paint/finger nail polish. The high road is to take the bike completely apart and dip it into Evap O Rust (or another industrial rust convertor) to chemically change the current rust. Apply that rust inhibitor already mentioned and reassemble the bike with appropriate assembly compounds (anti seize, grease, assembly paste if needed). The even higher way is to repaint the bike...

IME rust is rarely a structural concern and usually cosmetic, except for a few aspects. Like the seat post fit in the frame, same for a quill stem in the steerer. Both of these could galvanically bond to the steel if they are made of Al (or Al alloy), a very frustrating problem to get past. Most of the rust problems I see are with the fasteners and components. The safety and function will suffer if these are left to rust. Cables in housing, spoke nipples, der pivots and the like. All these could be cleaned in a solvent first (to clean off road grime) then examine for condition, replace if needed and lube on reassembly. Long term protection is more about routine servicing (cleaning and relubing) than a one time effort. Andy

Just put some oil or preservative on it. Or just not worry about it. I had many rusty steel bikes BITD. And I'm still here to tell about it.

If you want to be a perfectionist, then have the paint stripped and rusty areas dealt with, then repaint. While the frame is stripped, you might find a place that restores old cars. They might have a dip that they can put the frame in that will stop any rusting inside the tubes that you can't get too otherwise. Some of those places have a vat big enough to dip a entire car in. Use to be one nearby here. But that was 20 years ago that I'd seen them in action.

Hi, Andrew!!! Thank you sooo much. I’ve read your post twice, and I find it very informative and comprehensive. I really appreciate it. Especially when you said you see “no real concerns,” I sighed with deep relief.

Earlier today, I asked a bike workshop that specializes in repainting, and they told me a repaint would set me back about $280. I suppose an OA bath is included in the job, but that’s way too expensive for me.

Today, I also tried the easiest method of cleaning rust by rubbing it with tin foil dipped in water. Soon after, I regretted doing so, because I realized I didn’t have anything like nail polish at home. Eventually, I thought of peanut oil (commonly used in Chinese cooking) and sprayed a little on the frame, hoping it would form a thin film to stop moisture from intruding into the bare steel.

I guess I’m probably not that adept at fixing things on my own. Next month, if possible, I’ll take the bike to a more affordable workshop and see how they approach these issues. One mechanic said that welding a piece of metal to the seat tube would cost me 50 CNY ($7), which sounds very appealing. I’ll keep you updated when I make my next moves. Cheers!!!

dude.. just ride it.

That little spot of rust is just where the paint has been knocked off by something sharp, nothing to worry about.
Internally it does look quite rusty, although still superficial. If you could close the frame and fill it with rust remover (evap-o-rust, citric acid etc.) that would be good. Then dry it quickly/thoroughly and treat it with a corrosion inhibitor, it doesn't need to be Boeshield - we used to use LPS3 which is a spray-on sticky wax once applied, and it smells terrible so it must contain powerful chemicals.

I use LPS-3 for a rust inhibitor on my stock of raw tubes. Can't say it smells too bad, but I'm a shop lifer and my sense of smell has suffered over the years. For frame internals I prefer Frame Saver as it claims to coat the tube insides via the vapor when it's just sprayed in, and not just the liquid part. I still reposition the freshly sprayed frame all kinds of ways right after spraying, not wanting to rely on the vapors only.

But I suspect this is much like what chain lube is "best". The obvious answer is the lube (rust inhibitor) you're willing to use as needed. Andy

Very helpful!!! Thank you, sir. I think there is a huge chance that I could find a factory that could do the work. Although I'm a sort of "perfectionist", I might want to save the money for next bike. But I do really like the shape of this frame. It looks pretty much like a cheaper version of Moulton M60 to meHope I could find a more economical way to fix it. hahaha

Why are you welding anything to anything?

There really isn't anything to fix. If you don't like looking at the rusty spot, then put some touch up paint over it. But typically you'll be seeing the touch up paint spot. And that might bother a perfectionist too. So depending on how bad you are afflicted, the full paint job might be needed.

However, I'd just ride the bike, keep it clean. And dry. What could be more economical?

Don't do this.

Aye, I'll just leave it alone and enjoy the ride. Thx, my good man!!!

I'm wondering why did you decide to buy a used Dahon? Was the price really cheap? I've had a chromoly with a different frame and it developed play in the hinge from loaded touring. After 10 years my 2008 model became unusable so I had the hinge permanently welded together. The steerer tube fractured after 15 years. I've had an aluminum frame and it has developed a small amount of play too.

Although the frame that you have is a little bit more stable because of its pseudo top tube to help reduce the bending at the hinge, but without knowing the history of the previous owner I don't trust the hinges on used bikes. Just a little bit of play will gradually increase over time. So you might want to check to make sure there's no play and if there is, be careful with it and make sure it's adjusted tight.

Newer models have the steel cable from the head tube to the bottom bracket to help reduce the wear to the hinge. They cost around $500 at the official Hong Kong dealer and assume it's cheaper in China.

Well said, well said!!! Very detailed and practical advice. I really appreciate it! These issues had been bugging me over the past few days, and after hearing your insights on the causes of these rust spots, I'm no longer so worried about them. It means a lot to me that you explained whether the rust is superficial or deeply embedded in the steel frame, and you’ve managed to clear away all my doubts. I should also apologize for replying so late—I’ve been preparing for an exam on September 13. Sooo sorry about that!!!

Initially, I was thinking that maybe it serves to strengthen the seat tube by welding a piece of metal onto it, since rust might have already eaten away part of the steel. I'm still not sure whether my thoughts make sense or not.Help

Hi, Tommy!!! I bought this bike for 800 CNY (about $112). Yes, you’re totally right—a new Dahon is probably cheaper in our region. For instance, I suppose a new Boardwalk D7 costs around $350 in mainland China. As for the cable you mentioned, some Dahon enthusiasts complain that it was added to make up for lower tubing quality, so that Dahon could increase their profits. Just rumors, of course.

The reason I chose this Impulse D7 is that it’s quite niche—you don’t often see them on the online secondhand market. I’m not really a fan of aluminum frames, but I do like the Dahon Helios SL and HXX. Originally, I thought I could customize my D7 into something like a Helios SL, but right now I’m busy struggling with the rust, haha!!! Would love to hear about your touring experiences with your Dahon. Have you recorded them in a blog or something?

Roger that! I promise I won't.Thank you for offering me such valuable advice!!!

Welding a reinforcement can actually weaken the metal it's supposed to strengthen - the heat affected zone around the weld can make the steel more susceptible to cracking. Unless you have a specific problem that can be mostly fixed by welding, like a detached frame fitting, there's no point trying to make things better by randomly adding stuff that may not be in the right place, or the right shape or thickness, when you could easily be making things worse. I have old steel bikes, some are quite rusty, it doesn't worry me.

Hi, Andy!!! It’s such a delight to hear from you again. I just noted down LPS-3 and searched for it on Taobao (the Chinese version of eBay). I saw that one customer commented that LPS-3 has a smell like cream. Not only does that intrigue me, but it also proves that you were absolutely right in your judgment about its smell. I also looked up Frame Saver on Google and found that it’s out of production. What a pity! But I was wondering if there’s any alternative on the market that’s as good as Frame Saver. I’m looking for something that can convert rust into a neutral or stable substance. I’m also not sure how I’m supposed to apply Evapo-Rust to the inside of the frame, since it’s a liquid. Thank you, Andy!!!

New Dahon hinges have a little bit of flex but some hinge designs have more flex than others. If you stand next to the bike, put your hand on top of the hinge and push down on it, put a finger under the gap between the hinge plates, you can feel the gap increasing and decreasing a very tiny amount.

The new design with a cable actually reduces this flex because it is reducing the amount of bending on the hinge. And if you combine that with the newer jaws hinge type you cannot feel any flex at all. If properly adjusted.

Hi, Gru!!! It's so nice of you to explain this to me in such a clear-cut way. I now have a much deeper understanding of why it's not advisable to weld randomly on the bike. Also, I owe you an apology for getting back to you so late—I'm really sorry about that!Last weekend I had to take an exam, and I needed to get up super early to catch the 4:50 AM bus so I could transfer from subway line 6 to line 8 to get there. The exam was exceedingly tough and exhausting, and I ended up sleeping for almost 13 hours that night! Even now, one of my eyes is still a little swollen.

By the way, I would like to show you guys the bus I ride that morning. One of my biggest hobbies is taking photos of buses and subways.

I've used this product when Frame Saver was getting hard to find. It's very similar in feel and smell but is a tad thinner so runs a bit more.

Dipping/soaking in a bucket/tub is the usual way to apply Evap U Rust. I've used the same soak "tank" that I use for brazing flux removal, an 8" diameter PVC black water pipe that has had end caps glued on and a lengthwise opening cut into it.


I've also used a planter trough/container lined with plastic from a garbage bag. Andy

There really is no need to apologise for having a busy life. The only thing that might be considered impolite/annoying here is when people ask advice then never come back to tell us if they fixed their problem, and how. It's not even about saying thanks, just closing the circle.
I used to like buses and trains, I miss them because we drive everywhere now (or cycle for short local trips). The last time I used a subway was about 25 years ago, used them often when I lived in Germany.

Hi, Andy!!! You're such a kind person. These pictures are truly amazing and especially helpful to me. I'm certain that, with the picture you sent, I will be able to find this product without a shadow of doubt. And thanks to your superb demonstration, I now get to know how to use Evap-o-rust correctly and effectively.

BTW: That steel frame look really gorgeous, and I really like the way bare steel and raw lacquer frames look. Besides, your method is genius. Not only does your device nicely fit the size of a bike frame, but also saves much more liquid than does a bucket, since it is not so wide as it is long.

Plus, as a freshly graduated English major, I can still remember how grammar books taught us to use inversion and “end focus” when building sentences, hahaha. Sorry if my diction sounds strange to you. I just could help but use it here. Jingyuan Chen.

Hi, Gru!!! I can't agree more with your ideas, and I totally feel you. I think the phenomenon you mentioned is not just commonplace but also a worldwide issue.I see similar problems in our region as well. In essence, I believe it's about manners and courtesy. Whether in the online world or in real life, it's politeness and respect that make the world a better place.

The reason I really enjoy reading threads and blogs is that I often find the ideas and issues people are facing are alike—or even identical. Sometimes I deliberately check the time and year when the posts were written, and I genuinely feel amazed at the elapse of time and how the same situation can bring people from different periods together in one thread. Most importantly, the answers remain relevant and continue to shed light on future readers. That's why I think giving feedback is of vital significance.

Ahhh, it's a pity that I can't drive in my city, Beijing—not because I don't have a driver's license, but because I don't have access to a number plate.Anyways, bikes are enough for my daily use.BTW: German is really hard to learn, and I find difficulty in remembering all the cases in German language.