jliet

Hello,

Just found these when I removed the front track (non-drill) brake that was attached to a bike I bought. Presuming these are from the stress of the brake and not something that was done intentionally by frame builders (i.e. crimping to increase spacing? doesn't seem like it with the size of these).

Presuming this fork is not safe to ride after all...




Cheers.

Trakhak

The Framebuilders subforum might be a good place to ask.

jliet

Ah, let me get on that!

Dylansbob 

They don't look to be symmetrical from the pics. My first thought was a caliper brake getting pushed back hard enough, but without a drilled crown that seems unlikely. Even a "Keirin" brake clamped on should create some symmetry.

jliet

I think it's my picture - they are indeed pretty symmetrical (or very, very close to) if I feel the crimps, which is why I felt it was weird. And it was indeed a keirin brake, but it did indeed have rubber padding, so it's still weird as to how it happened...

Rage

I think they might look asymmetrical because one side might have been clamped down tighter’n the other?

uncleivan 

They make the keirin brake mounts in round and aero depending on the type of fork. My guess is they used an aero clamp on round fork legs...they look round to me.

jliet

Yes, this is the conclusion I reached in the end as well. They are standard, round fork blades and the mounts they used were aero... Which is unfortunate.

markk900

It truly is unfortunate..... but I have a question - why do those dents make that fork unsafe (if indeed they do). That type of dent would make the tube more susceptible to bending in the direction of the crimp, but that is not where most of the force is directed as far as I can imagine..... so is the fork unusable? Or just ugly now?

gugie 

Steel frames can break and still be "emergency rideable". Bob Freeman (Bill Davidson's ex-partner) tells the story of seat stays breaking at the seat lug in the middle of a ride, and a toe strap keeping it all together till he got home (riding gingerly). Forks are a different story. If that breaks or collapses, odds are you're going down. Without analyzing the stresses on the fork and perhaps doing tests that may or may not be destructive, anything hinkie on a fork, I'm staying away from it. It might probably be ok to ride, but the risks are magnitudes higher than if a frame joint or tube failed.

Hard no IMO.

uncleivan 

While we're at it, how about a picture of the frame? Japanese? American? British?

bulgie 

isn't the downtube kinked in, at the point of the lug? Lug acting as a "can opener"?
(Who here is old enough to remember can openers?! Gone the way of buggy whips.)

Could be the blades and DT both got munged in the same "event".

oneclick 

When I first saw the damage I wondered if the difference in the heights on the two blades was a sign of a collapsing wheel; that possible downtube kink could be from the same event - a collision/crash?

easyupbug 

Very wise words not universally appreciated. Risk is likelihood times consequence; in this and many other cases while some would view the risk acceptably low, being a fork the consequence of failure is very serious.

jliet

It's actually an 80s Italian (most likely) Cambio Rino, more images can be found here.

In reference to this, it does look weird, but I believe this is due to the ovalised Columbus tubing and the way the welding was done. Having said that, later Cambio Rino/Gardins were known for having questionably and variable build quality. In this instance though, looking at the other lugs, etc and also at the steerer/headset, I don't think there was a front collision.

Please also note the headtube angle which they were famous for. A very weird frame, all in all.

jliet

Yes, fork failure is definitely not something that will end in a 'safe crash landing' for sure, aha.

Having said that, I was interested to try and see where the stresses actually occur, so I took the fork from this cad file and put it in ansys and played around. Please note the disclaimer that I am, and will not, use this to justify riding this and anyone else who finds this thread in the future please note there are a lot of assumptions made in this model. It's purely academic to understand the fork flex/strains/etc.

I tried one big hole in a fork (image 1) which does get strain of up to 1000MPa (and yield point for T6-Al is apparently around 270 [?]). I then tried 2 unform cylinder cut outs which fared much better. Please note, reality is very different especially with dents (+ also I only applied basically simple forced, you cycling and hitting a pot hole at a certain angle is very different, there's also creases/fractures/non-perfect denting as opposed to what I did).




Anyway, I will not be riding this fork - not worth the risk and injury (and especially when it costs £50 to get a new fork).

cudak888 

Gardin may have been known for steep angles, but I don't buy it for a minute that the headtube angle was like that to begin with.

Even in the wide shot, it's clear that the frame has either had a front ender, or it couldn't take the braking forces of the clamp-on brake at one time. Either way, it has kicked the headtube steeper, creating fairly visible points where the bottom of the headlugs have pushed the tubing upwards into the frame - it's a lot more pronounced on the downtube. Also, the top tube is sloping upwards to meet the headlug; another sign of front-end damage.

There's a lot here on this frame and fork that make it more trouble than its worth. Did you buy it recently? Any chance you can get your money back and look for a different frame?

-Kurt

gugie 

Thanks for doing that! Modeling gives us better insights into mechanical behavior.

jliet

Not sure, to be honest. The headtube angle (when I measure side on, not from pictures above) is 77/78 - this is apparently standard for what (some) Gardin frames had. For reference, here's the cambio rino competizione, and most of these (keeping in mind it's not fully accurate due to picture angles) seem to also be in the similar range of 76-78. Here is another example of a Rino track where the top tube slopes upwards to meet the headlug:



Some more lug examples:




The headtube angle is not what worries me the most, and I don't think you're correct on the sloping head tube, though I agree on the bend where the top tube meets the head tube is suspicious. Though, looking at these other examples of ovalised Columbus tubing, the bottom part also seems to have a sort of bend (which does look similar to on my frame when taken from that angle).

Either way, I will not be returning it! Go it for $100 for the whole build, since I wanted the Sugino Super Mighty track crankset 165mm - that alone is worth double what I paid (not even looking at the wheelset). I will take it to a local framebuilder when I can and get an opinion though.

cudak888 

I tend to ignore measurements when assessing a front ender when there's evidence of damage; it's super easy to measure the angle wrong if the bike isn't perfectly level.

Still, agree 100% - that price is definitely is worth it just for the crank; even better with the wheelset. Good score!

Best of luck with it - if that's not heat treated tubing, it may be possible for the framebuilder to cold-set it with very little evidence of the front-ender.

-Kurt