Wednesday, December 8, 2010

'Fork's Bent?'... Suspicious Cracks in the Paint Cause Concern

The phrase "fork's bent" has become a private joke of sorts in vintage bicycle circles.  Almost any time somebody posts a picture of their "awesome vintage find," there will be that one person who comments that "the fork looks bent." Most of the time, the fork is not bent and it's just something to say - or maybe the angle or the lighting in the picture are misleading. Nonetheless, the possibility of a bent fork or frame is certainly something to watch for in vintage bikes. If a bicycle is steel, a bent frame or fork is not necessarily tragic - steel is flexible and the bent portion can usually be straightened. Cracks, on the other hand, are of greater concern.

During my visit to Geeekhouse last week, the guys were looking at my Gazelle and pointed out that the bits of cracked paint underneath the fork crown could indicate cracks in the surface of the fork itself. Needless to say, my heart sank.

I noticed the cracked paint before, but didn't think anything of it. The fork blades in of themselves are not deformed and there are no indicators that the front end of the bike has been in a collision. In an impact strong enough to bend the fork, surely there would have been some other damage - but there is not a scratch anywhere. The bicycle also handles absolutely fine - better than fine - with no indication of anything "off" in the steering.

It would be easy to dismiss the cracked paint, if it were not for one red flag: The cracks are symmetrical - right underneath the fork crown, on both the right and the left blade. How did they get there, and how can we tell whether it really is just cracked paint or an indicator of some sort of trauma to the fork?

I was speaking to a local frame-builder yesterday, who advised to check for similar paint cracks in the back of the fork blades. There are none; the paint is cracked only in the front. To him, this was an indicator that the fork could be fine - as stress fractures typically happen in the back and not in the front of the blades. He also pointed out that even if the fork has been bent and reset, or even if there are hairline cracks, a massive Dutch fork like this can probably take it, without it being a safety issue. No doubt there are loads of people in the Netherlands riding ancient beaters with visibly bent forks.

But the bottom line is, that we simply don't know what's going on under that cracked paint. To find out for sure, I would need to remove the paint from the fork blades and thoroughly examine the steel underneath - which I am reluctant to do, as the original paint is so nice. Is there any way to diagnose while keeping the paint intact? Any suggestions or thoughts are welcome.

49 comments:

  1. At least it's not carbon fiber! That would shatter in seconds. My suggestion is to keep riding, but look for replacement forks if the day ever comes. Surely vintage bicycles are great, but finding components for them can be tricky sometimes.

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  2. Also, update your "buying a vintage 3 speed" bicycle page. This could come in handy for anyone else out there looking for a bike.

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  3. Based on the sheer number of steel bikes I see with slightly tweaked forks, I've begun to suspect that at least some of the damage is due to braking, not crashes. If you think about it, it's not that crazy of a theory. After all, many step-through frames bend a little in the seat-tube, right? I would love to hear what the experts think.

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  4. Also, I once owned a vintage 28" roadster with massive front impact damage. The impact was apparently so severe that the steerer tube was bent and cracked, along with the rest of the fork. But there was no visible damage to the frame or fender and the wheel was marginally rideable -- the rim buckled slightly.

    So, if in fact your fork was damaged in a crash, it's possible the wheel went undamaged, or was replaced.

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  5. lyen - This bike has a very weak front drum brake, but still, you never know. The wheel definitely looks original to the bike based on the aging and wear and tear patterns; no components have been replaced as far as I can tell. (Plus, the previous owner brought the bike to the US from Europe some time ago. Until 2 years ago there were no Gazelles imported and nowhere to get replacement components.) I am trying to imagine a scenario where the fork would be bent right under the crown, but the wheel completely undamaged. Hmmm.

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  6. When the bicycle was being transported from Europe it may have had the front wheel and possibly mudguard removed for ease of transport. It doesn't seem to far fetched to think that it may not have been treated well in transit; the fork could have been stressed without the wheel being affected.

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  7. If you have a friend/contact with access to an xray machine you can take the fork and have it xrayed. If I recall correctly, xrays are used to test for welding cracks. You have to use a dye to penetrate the crack, remove the excess and then run the xray.
    That seems like a lot of advanced trouble, but it would be pretty cool to do it.

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  8. ...and a thought that just occurred to me. Steel and brass expand and contract at different rates. Paint does not tend to do so very well, especially lacquer which is very hard and brittle.
    Those cracks could very well be just the edge of the brazing/steel temperature transition cracking the paint apart. I have seen that happen in a number of lacquered wooden clock cases between material transitions.

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  9. If you are concerned, you could proof load cycle the fork as in my "carbon" series. If there is a safety problem, it will be more evident under loading. If not, the paint is undamaged.

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  10. Could these be scrapes and not cracks? I cannot tell by looking at the pics. Putting on or taking off a rack or something like that could result in symmetric scrapes. Did you notice that the paint in this area was not cracked/scraped when you got the bike, ie is this something new?

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  11. I do not have an answer to your question, but can relate my experience. In the mid-80's, I had a Bianchi road bike on which I was involved in a accident. A car turned left in front of me and I plowed into the car and flipped the bike (I recall seeing blue sky). I took the bike to a shop and they checked it out on some sort of alignment device. It was pronounced sound. Months later, paint cracks developed on the head tube where it met the seat and down tube. When riding the bike very fast (50+ MPH) down hill, there was a shimmy in the front end. This was very disconcerting, so I avoided these speeds, which wasn't hard because that kind of velocity rarely happens on my rides. My point is, I think it would be possible that a collision could have caused this damage without seeing other signs of damage. My wheel and forks survived the 'endo' just fine and it wasn't until months later that I even noticed my paint cracks.

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  12. "I am trying to imagine a scenario where the fork would be bent right under the crown, but the wheel completely undamaged."

    Thumping a garden wall because you have a very weak front drum brake would do 'er. You can bend the frame itself that way with no damage to the wheel or fender at all. A high curb might do as well.

    Wheels are very strong longitudinally. Forks are weak at the stress riser where slender blade meets beefy crown.

    A crack in paint doesn't imply a crack in the underlying material (although that may be the cause). It just means that the paint has been stretched beyond it's elastic limit.

    Steel is "bendier" than paint. Take a paint chip and try to bend it. Now take a paper clip and try to bend it.

    The other place for people examining a vintage bike to look for cracked paint is the downtube just behind the headtube lug. Cracks there imply the frame has been thumped pretty good.

    "Is there any way to diagnose while keeping the paint intact?"

    No.

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  13. Wheels rarely get damaged in a front end crash, but the forks are the first to go. Just think of the fork blades as a big lever, bending at the next strongest spot [the fork crown].

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  14. I wouldn't worry about it.

    These bikes are pretty sturdy; as you noted steel forks are often reset after minor damage (road falls) and rear triangle can be cold set.

    I'd just ride it reasonably (don't try ramming cars or sharp turns are 40mph); I think you'll have ample warning if there really are any problems

    Stephen

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  15. i have seen several raleigh sports step-throughs where there is an identical pattern of cracking of the paint right above the lug where the sloping top tube meets the seat tube. in all those cases, the seat tube has an ever-so-slight kink from bending right at the lug. this is one of the inherent weaknesses in the step-through frame design (a weakness which, on mixtes, is eliminated by the extra set of seat stays).

    so based on this, my hunch would be that there was stress at the fork crown of your fork from a possible front-end blow. however, normally, forks bend along their length, not just at the top. it's possible that the fork had indeed bent and a bike shop or frame shop straightened it, ignoring the paint cracks at the crown (i doubt there are cracks in the steel).

    as for replacing the fork, i doubt the fork is proprietary to gazelle. by the 90s, most major dutch manufacturers were using off-the-shelf parts, including frame parts; gazelle not excepted. i wouldn't be surprised if gazelle just sourced a 28" generic fork and slapped their sticker on it. it's possible that DBC boston has some dutch forks lying around, and i'm also guessing that if they did, they'd be in black!

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  16. Is it possible that the fine folks at Geekhouse could fabricate a new fork for you if the Gazelle's is indeed damaged beyond repair?
    That might be an expensive fix,but if you want to keep the bike, it might well be worth it.

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  17. Velouria,
    One other "non-invasive" step that you could take, if you haven't already, is to remove the fork from the frame and examine the steerer tube. Sometimes, a front-end collision will either slightly bend the steerer tube (put a straight edge on it) or will create a slight bulge on the back of the tube as it enters the form crown. On bikes with closer tolerances and better components (no offense to Linda!), this sort of damage will often cause binding or uneven adjustment in the headset, but I doubt that this could be used diagnostically on the Gazelle--it may not have ever had a perfect adjustment.

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  18. This may be more than what you want to get into, but it's possible to use ultrasound to view cracks and deficiencies in steel- we sometimes have it used on field welds that are critical. A big steel fabrication place like Metrowest would know who to direct you to, but it would probably be a couple hundred bucks.
    You should appeal to the MIT community and see if there's some grad student in metalurgy or materials science who would help you out.. Maybe contact the copenhagen wheel folks for recommendations.

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  19. oh, another possibility, velouria, in case you can't find a genuine dutch replacement fork: i once picked up a ladies' DL1 (for $10!) that had a severely bent front fork; it was salvageable. after unsuccessfully scouring ebay and CL for weeks for a replacement fork for 28" wheels, i bought an eastman DL1 clone fork from yellow jersey for $40. the steerer tube is raleigh threaded, meaning it used raleigh's proprietary 26 TPI threading for the raleigh headset, but you could have a bike shop re-tap it to standard ISO threading and reuse the gazelle's headset.

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  20. I've never heard of steel cracking as described. That is usually something that happens to aluminum. I've read that aircraft are inspected for cracks using some form of X-ray device. I'm not sure if it is possible to find a shop that could do that form of inspection on a bicycle. And would it be worth the cost?

    My wife's 1959 Raleigh Sports has a bent seat stay. The shop to which she brought the bike advised her that straightening the stay would make it weaker, and that the best thing to do is leave it bent.

    Dan.

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  21. An adventurous, tenacious person would try to find, say, a dentist to X-ray that part of the fork.

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  22. you could take the fork off and fill it with pressurized water/air and see if any leaks out through that area. This of course will not work if the tubing isn't connected, another way would be to take the fork off and gently tap each side and listen for different tones (if the metal is cracked it might sound different), and finally you could x-ray it and look for cracks, they do that to bridges sometimes. Gonna guess that might be a bit too much trouble.

    I say you keep riding it and not worry about it, that fork will most likely fail gracefully if it fails. Thing is sturdy.

    That or just paint the cracks shut and see if they come back, if the area of the fork is flexing the new paint will also crack eventually.

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  23. Paint is not especially flexible. It will certainly crack from much less stress or deformation than could damage the fork. It's probably fine :)

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  24. If you happen to be friends with an ultrasound tech, they might be willing to take a peek in the fork. Then, you'd know for sure.

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  25. "I've never heard of steel cracking as described."

    Steel cracks all the time. I've lost two frames myself from cracked down tubes and seen dozens of others. Cracked forks are even more common.

    As for your wife's seat stay, your shop is full of it. Probably because they can't do the job. Find a new one.

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  26. Would it be possible to remove the paint just from right under the fork crown, and then just kind of touch it up with some glossy black paint afterwards? It would probably weather fairly quickly to where it matched, especially if you left your bike out in the rain a few times :)

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  27. Thanks so much for the feedback to all.

    I did notice the cracks in the paint when I got the bike, so they are not new. Vintage bikes have cracked and chipped paint all over the place, so I did not think anything of it. The blades of the fork seem fine; I do not see any distortion. And as several have said - steel is much more flexible than paint, so cracked paint does not necessarily imply that the steel under it is bent. Still, when the possibility was pointed out to me by people who know bikes, I couldn't just ignore it.

    Though I know people who perform x-rays and ultrasounds, I do not know them well enough where it would be appropriate to ask them to ultrasound/ x-ray my fork -though it's an intriguing idea : )

    I also do not want to replace the fork, unless I can find one from the same model Gazelle as this bike. But even then I am not sure I want to spend the money. After all, I have no idea what the history of this bike is and what else might be wrong with it, if indeed the fork has a problem.

    My own instinct is that given the lack of deformity in the fork itself, it really might just be damaged paint. Jim P could be right that they are scrapes from an attempted installation, or others can be right that some very minor bending happened in transit when the bike was being brought to the US in the first place, and the paint cracked even though the fork is fine.

    I think I will take bostonbiker's advice to seal the cracks in the paint and see if they come back; that could be informative.

    One question I have: So what is the worst case scenario if the fork indeed has micro-cracks in that spot and fails? Will it snap in a matter of seconds, taking me down in traffic, or will it creak slowly, giving me time to deal with it?..

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  28. somervillain said...
    "... i doubt the fork is proprietary to gazelle. by the 90s, most major dutch manufacturers were using off-the-shelf parts, including frame parts; gazelle not excepted. i wouldn't be surprised if gazelle just sourced a 28" generic fork and slapped their sticker on it.


    Gazelle was late to the party of getting everything outsourced. Based on my investigation (back when I was looking to buy a new Gazelle), they maintained their own factory in the NL until 2006 or 2007 in which they continued to produce the classic line of bikes with fairly few changes in design over the decades. Only in 2006/2007 did they sell the factory and equipment, and began outsourcing production to China, as Batavus and the other Dutch brands do. The post-2007 outsourced Gazelles are easy to differentiate from the earlier models, as the frame construction is a bit different (welded rear stays) and the components are different. I am 99% sure that my mid-90s fork is proprietary to Gazelle. Plus the chromed crown has little Gazelles on it...

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  29. I bet the fork is fine. It could be that the paint has not adhered to that area due to flux residue from the brazing process. Or it could be that the forks have been tweeked- and straightened. The integrity of the paint on the rear of the blade is a good sign.
    Lots of companies specialize in Non-destructive testing(NDT) and could probably detect stress cracks by using an Eddy Current or similar process. The beauty of steel is that it is much more forgiving than aluminum.

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  30. "the possibility was pointed out to me by people who know bikes"

    If it were light gauge chrome-moly there would be cause for more concern. The stuff is more brittle than hi-ten. Because it's heavy gauge hi-ten it is even possible to repair a crack by welding.

    "bostonbiker's advice to seal the cracks in the paint"

    This works. It's best if you clean the area of old paint first though, or the results can be misleading. This will also let you clean up the rust, which will spread UNDER the paint along the crack. Use a brittle lacquer for best results, but be careful of melting original paint. The stuff is "hot."

    You won't be able to entirely preserve the paint this way, but you can paint a band that that will look like an intended bit of detail.

    "Will it snap in a matter of seconds"

    Not likely at that location. The normal forces on the fork will actually press the crack closed. That's why stress fractures happen on the back side.

    "will it creak slowly"

    Most likely. Possibly for years.

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  31. Peppy (the mechanical cat)December 8, 2010 at 1:32 PM

    I think when I have some time off we'll take the fork out of the frame, strip the paint and steelwool the metal. Then after examining the metal we'll repaint with black auto enamel & reassemble.

    Until then it sounds like the consensus is that it's safe to ride.

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  32. velouria said:

    "Only in 2006/2007 did they sell the factory and equipment, and began outsourcing production to China, as Batavus and the other Dutch brands do."

    i wasn't referring to outsourcing production outside of holland. if you look at the lugs, rims, handlebars, grips, lights, fenders, chaincases, fork crowns, etc... of most dutch city bikes made from the 1970s onward... i'm talking about the dutch bikes made in their own brand's factories in holland... they used highly standardized "parts bin" parts, even entire framesets. yes, they were assembled in the netherlands with parts made in the netherlands, but there was little brand distinction, aside from putting proprietary stickers and badges on everything, at least on the everyday city bikes. the fenders on my wife's 1973 union are the exact same fenders that DBC boston was stocking, 35 years later, and were the same fenders that my friend's 1980 batavus had. they obviously came from the same tooling. that's why i think a stock 28" fork from anywhere in the netherlands has a good chance of being identical to the one on your gazelle. it may even have been made at the same factory.

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  33. somervillain - The Gazelle forks look fairly unique compared to the other Dutch bikes I've seen. Even if they were sourced from the same factory, the Gazelle has a distinct fork crown and for me it's one of the things that makes the bike special.

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  34. I wonder if truss rods may be a useful addition to the bike at this point. I honestly don't know, but they wouldn't look too out of place.

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  35. velouria, what appears to be the fork crown with the embossed gazelle insignia is just a replaceable chrome or aluminum cap placed on top of the actual lugged crown. that's how it is on both of our dutch bikes. it slips over the crown and is just held in place by the headset.

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  36. If the forks were bent backwards by an impact,
    it would not likely cause cracks in the fork
    blades unless they were severely bent. However, there may be damage to where the fork blades braze into the fork crown, and where the fork crown brazes to the steerer.

    So *I* would:
    - remove the fork
    - remove the shiny cover over the fork crown
    - check for any more cracked paint
    - pick off the already cracked paint
    - inspect metal underneath
    - pick off paint covering all brazed junctions at the fork crown (both blades and steerer - above and below crown).

    Inspect thoroughly. Looks for cracks
    or any distortion. Also check the steerer
    for straightness, or any bulging as Eric said.
    If you want to go whole-hog, you might want to take them to a framebuilder who does fork repairs
    to look at them and check for alignment in a
    fork fixture (jig).

    If all looks OK, then repaint the top of the forks
    and reassemble. The shiny cover on the fork crown
    will hide any paint mismatch.

    With newer Gazelles that use the aluminium drum brake, any front impact tends to distort the drum, so when you apply the brake, the brake pulses - gets stronger and weaker with each wheel rotation.
    I do not know if your steel drum is prone to this,
    but for aluminium ones it is a good indicator of abuse.

    I don't think it was the front brake that caused this. This model brake is fairly weak and it stresses one blade more than the other, whereas
    you have symmetrical paint damage.

    Also check for any paint damage at the junction of the head tube and the "top-tube" and down-tube.

    As to the question of whether you will get any warning - it is rare that both blades break
    together, so yes you probably will. However steerer failure often does not give much/any warning, hence the importance of checking there.
    But as Kfg said, the steel these are made of is capable of a bit of bending and bending back,
    just make sure the brazed joints are fine.

    John I

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  37. somervillain - I realise that. And while I do want to retain those chrome overlays with the embossed gazelles, I also mean that the shape of the crown itself is distinct: the slope, the overall form, etc. For instance, it is different from the fork crown on your wife's Union. Furthermore, based on what I have seem, the fork crowns on Gazelle differed depending on the model - I have seen at least 3 distinct shapes, congruent with different models. I think it would detract from the historical feel of the bike if I just put a generic Dutch fork on it.

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  38. I weigh 372lbs and managed to bend my Raleigh DL-1
    fork severely. At first I started to keep adjusting the rods for the front brakes.On my way home one day the tire start rubbing the fender,and the brakes popped
    out of the guides. The paint was and still is all in tact. So I guess what I am saying is, yeah it is a tell tale sign, but it is just that a sign. I would look for other signs, like it not tracking well or overly creaky noises from the front etc..

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  39. John' I's and Peppy TMC's suggestions about a full inspection are sound. It's something that you and MDI/Peppy could manage in an hour or so with the proper tools. Once you get that crown cover off, you'll get the full picture with the fork blades and lugs. Also, inspecting the steerer tube will tell you if the bike has been crashed and straightened.

    Plus, it gives you occasion to clean and lubricate the headset.
    I wouldn't worry...

    Cyndy The Neighbor and I had a new steerer tube brazed onto her 1957 Phillips forks by a local frame-builder, as the original was so bent from impact that it couldn't be straightened. And it's a Dunelt/Phillips 28" fork. Not made since probably 1965, and a real rare bird. 'Twas less than $100, excluding paint, which it's getting anyway.

    You have some of the best frame builders currently working amongst your sponsors. I bet ANTMike, Brian H, or The guys at Geekhouse could *build you* a replacement fork using the original crown lug, if need be.

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  40. As a retired engineer my advice is to get the forks checked for metal fatigue which can happen exactly where you see paint cracks.

    To check you will need to remove some of the paint in the area where you see the cracks then go to an automotive or machine shop to buy a "disclosing kit" for cracks with two part spray. Once cleaned free of paint spray on the dye then wait a bit then the white top coat. DO A LOT OF COVERING OF WHAT YOU DON'T WANT STAINED! If after the top coat is dried IF you see red crack lines your fork is cracked and will need re-enforcing welds. If no red lines then your good to go after you clean off the dye & disclosure. (You can't paint over it!)

    Since your bikes paint is lacquer you will need to test a small spot with your repaint lacquer to see if the two paints agree or you will get bad paint wrinkling and/or lift off. DO NOT USE ANY OTHER PAINT BUT LACQUER.

    Whatever you do I would NOT ride that bike until you can verify the condition of the fork. Metal fatigue , once started, will continue until failure of the part involved.

    Best of luck,
    Walt D

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  41. There are ways to find out whats underneath the paint but unfortunately it would cost a lot, unless you have a friend with access to equipment and materials, like x-ray.

    http://en.wikipedia.org/wiki/Nondestructive_testing

    Or, my understanding is you are located near MIT, so, maybe you could take the fork out and have those engineer geeks mount it on a bench and do some kind of tuning fork-like vibration test.(for example, tapping on the good fork blade and then on the suspect blade?)

    http://en.wikipedia.org/wiki/Tuning_fork

    Somehow there's a way to get to the bottom of this non-destructively. The question is how to find out free or cheaply.

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  42. I really wouldn't worry, just keep an eye on it and don't overload the forks. These bikes have evolved since the 1890s to be strong enough to carry a heavy rider plus luggage and/or passenger, with enough strength to spare for emergency stops and collisions. Compared with a lightweight racing bike they are virtually indestructible. Plus mild steel frames do not break catastrophically, and if any cracks do eventually enlarge you will be aware of something being wrong long before the forks actually snap.

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  43. Oh, how sad. I hope whatever the situation is, you are not forced to give up your perfect bike.

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  44. kfg,

    Thanks for the information on steel cracking. That's interesting and I'm glad to learn that it does really happen. I'll have to do some more reading and research.

    And I will ask around at other shops to see if there is someone who knows how to repair the otherwise lovely bicycle.

    Cheers,
    Dan.

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  45. As has been mentioned though, steel cracks in a very different way from aluminum. Neither of my bikes that cracked failed catastrophically. In fact I rode the second for a couple of weeks before I figured out why it "felt funny." I still have the frame and could assemble it and ride it again if I had to for some reason.

    The other one never felt funny at all. I just happened to notice the crack forming because it began at a water bottle boss; so I stopped riding it.

    They were also both high milage (over 100k for one of them), lightweight racing bikes that had been pressed into service beyond their design parameters; as well as a fair amount of racing.

    All the steel frames I've seen that appeared to fail catastrophically showed signs of having been ridden for a long time after the crack started to form.

    Some of these were low mileage (comparatively), heavy gauge hi-ten bikes, but with design flaws that created unnecessary stress risers. These sort of design flaws don't usually last very long in production though, so "venerable" designs don't have them.

    As for the bent stay, Park even makes a tool to straighten them. They wouldn't do that if weren't both a common and acceptable procedure. Some shops aren't as good as some others though, and some would simply prefer to convince you you need a new bike.

    But some shops actually build a trade around frame repairs. Try to find one of those in your area.

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  46. Dottie - I guess nothing is perfect : )

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  47. i was lucky enough to visit the factory in Dieren and the factory is still there, they just dont build the frames there anymore. Raw frames come from all over and then are painted and assembled in the original Gazelle factory to this day. That fork unfortunately is no longer proprietary, only the chrome crown cover is. But luckily a brand-new replacement fork from Gazelle is still able to be purchased, for about 100 bucks.

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  48. The fork looks bent. :0

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