Bicycle Mechanics - what do these paint crackles mean?

off a colnago fork.

It looks like it could be the result of a crash. Check your steerer tube carefully to make sure it is not bent. Check to make sure it is straight at the junction where it joins the fork crown.

-j

Looks like a bent fork.

If you know that the forks have never been crashed and they are straight then what you have is an example of how a brittle paint job is less flexible than the underlaying body and how it can crack when flexed in compression or tension. Assuming that this is the front of the fork legs then what happened is that the constant flexing forward due to springing when hitting bumps and potholes flexed the legs more than the paint could withstand and it failed from compression of the paint film and a failure of the bond between the metal and paint film.

It means the metal underneath the paint is cracked. bk

If it was mine,It means I need to remove the paint and look at it more closely.Magnaflux it if you don't actually see any cracks.

That's not a paint flaw. That's a bike that was bent.

I'm assuming that the gold coloured cloverleaf is on the front side of the fork. Not many cases of graphics of that sort on the rear side. Generally a collision would bend the fork leg BACK and the cracks in the paint or in the metal would occur on the front. So a paint bond failure due to the metal stretching from road roughness and vibration is far more likely than the tales of doom and gloom given so far.

It would certainly be worth removing the paint and checking things over though. The paint is going to eventually chip away in any event.

If it wasn't crashed then it was not properly prepared at the factory prior to painting.
Paint is flexible. Look at all the other bikes that don't have that problem. I'm sure their forks flex also.

Not all paints are all that flexible. Also a lot depends on the bond to the substrate and the adhesion with any primers used. Back in the late 80's and well into the 90's when the shift was made to low volitility paints a lot of things came out on the market with paint bonding issues. There were a sizable number of cars with this issue. I know because I had one of them and by the time I junked it the darn thing looked like it was a snake shedding its skin. I suspect that this Colnago frame is another example of such a thing. The OP also has a companion thread about this frame running in parallel with this question about the forks. And when you see the chips out of the paint on the frame and how it looks like you could slip a fingernail under the edges and lift off another big chip I think you'll all agree that this is more a paint film failure than due to fork damage.

In any event it's always good to check for signs of impact. In the case of a fork ensuring that the upper portion of the legs is parallel to the steerer tube is always a good sign that all is well. But if bent back by more than a degree or two that trouble is locked away.

The crack is right through the metal, that's grease seeping through. Do not ride that fork.

I'd be as concerned about the corrosion that's started under the paint as I would be about the cracks themselves. In any case, get the paint stripped off (preferably chemically) and have the forks magnafluxed. IF they pass the 'fluxing, consider phosphoric acid to halt the rusting before repainting.

They mean it's time to get a new bike.

Enjoy

People deal with a little rust on their steel bikes all the time. I can't believe the sudden onset of woe and doom that I'm seeing in this thread. At worst there's a little bit of rust going on behind the cracks in the paint. If the metal isn't pitted badly below the paint then there's no big deal about stripping the paint off and re-finishing the forks and using them for many fun filled years to come.

People deal with a little rust on their steel bikes all the time. I can't believe the sudden onset of woe and doom that I'm seeing in this thread. At worst there's a little bit of rust going on behind the cracks in the paint. If the metal isn't pitted badly below the paint then there's no big deal about stripping the paint off and re-finishing the forks and using them for many fun filled years to come.

Anyone that has spent time working on bikes would recognize those cracks as the result of a front end collision.
Yea, you could ride a bent up steel frame for years but why would you?

Enjoy

So why are the cracks on the REAR side of the fork? The Colnago graphic indicates the front side of the fork and it doesn't have any cracking. Having said this I've also already posted that the forks should be checked.

Check out the OP's companion thread about the entire frame. There's lots of evidence from the nature of the chipping on the frame that the issue here is simply a paint bonding failure coupled with some neglectful handling.

Not all paints are all that flexible. Also a lot depends on the bond to the substrate and the adhesion with any primers used. Back in the late 80's and well into the 90's when the shift was made to low volitility paints a lot of things came out on the market with paint bonding issues. There were a sizable number of cars with this issue. I know because I had one of them and by the time I junked it the darn thing looked like it was a snake shedding its skin. I suspect that this Colnago frame is another example of such a thing. The OP also has a companion thread about this frame running in parallel with this question about the forks. And when you see the chips out of the paint on the frame and how it looks like you could slip a fingernail under the edges and lift off another big chip I think you'll all agree that this is more a paint film failure than due to fork damage.

In any event it's always good to check for signs of impact. In the case of a fork ensuring that the upper portion of the legs is parallel to the steerer tube is always a good sign that all is well. But if bent back by more than a degree or two that trouble is locked away.

If I recall correctly, 80's and early 90's Colnagos were known to have paint issues.

Rust can cause paint cracks that are perfectly straight? I don't think so.

So why are the cracks on the REAR side of the fork?

I've seen rear cracks caused by forward bending before - from repeatedly coming down hard from wheelies or going down off a curb.

Not rust but the stretching of the rear side occurs on the rear of the fork legs when going over rough roads certainly does produce this sort of paint bond failure if the paint is not 100% up to the job. Rust blooms in the cracks would come afterwards once the paint opens up the steel to the elements.

None of this is suggesting that there is not some possible collision damage to the fork. That would require further checking of the fork. But the sort of paint failure I'm seeing is entirely possible without the aid of collision damage. And again the fact that the paint damage is on the REAR of the fork leg and the sort of paint failure on the frame would suggest that this is likely the case.

Thankyou Vredstein. Posting this question on the C&V forum would very likely turn up an answer if there is such a history.

I've seen rear cracks caused by forward bending before - from repeatedly coming down hard from wheelies or going down off a curb.
But you'd have to admit that it would be unlikely to find something like a Colnago road frame that saw that sort of history. Besides if the paint itself is just suffering from issues the steel forks would be just fine in behind the damaged paint.

If it was mine,It means I need to remove the paint and look at it more closely.Magnaflux it if you don't actually see any cracks.

I got to agree with this...if it was mine I would do this before I decide what to do with the rest of the frame. I didn't see any real damage on the frame other than (what I THINK are) paint issues, but it was also hard to tell from some of the shots maybe if you posted less close ups and more wide veiws.

sorry, I should have included more and clearer pictures.

for the record, the crackles are on the front of the forks.

and laying a straight edge (or as straight an edge as I have that length) along the front of each leg, doesn't not look encouraging.

Note that the kink that the ruler is sitting on is below the crackles. And looking at the side pictures it's quite obvious that the fork leg starts out as a constant width upper portion then transitions to a tapered lower portion. All your latest pictures show the fork to be just fine. I'm still sticking to this being a paint bond failure issue. Note how the one part is chipped out cleanly almost like a wall tile that came loose and fell out. Get into that spot with a small knife blade and I'll bet you can lift away a lot more paint that is only semi held on to the base metal. I'm not seeing anything to support a collision being the cause. Even the steer tube is nicely canted forward as it should be in the one picture.

The only way to know is to sand or peel the paint off to the bare metal in that area.

OK, thanks much for the side shots. It seems highly unlikely that the same paint flaw would occur on both fork blades in pretty much the same spot, and only toward the front of the fork. As for where the "kink" is, when a fork has a minor front impact the area where the paint cracks is stretched, thus the cracks. That area can easily be flat and the area below it appear to be curved. Having seen scored of bent forks (happens a lot when you run a repair operation in a university town) the pictures shows me a classic front impact.

That being said I can tell you it's very doubtful the integrity of the fork has been compromised such that you have to be concerned. It will have slightly reduced your fork rake and would therefore make the handling more sensitive. Actually if you had the original specs for the bike you could compare to perhaps determine how much things have changed. Correcting a small deviation still would not concern me, although it would probably make the paint problem worse!

The only way to know is to sand or peel the paint off to the bare metal in that area.

and that is what I plan to do.
though BCRider's point reminds me that what I should do is compare the line of this fork to a certified un-accidented colnago fork from a similar Piu model.
anyone have one they can hold a straightedge up to and see whether it is a straight line?

Peter

You could also do the straightedge test at the back of the fork blades to compare! If you post a pic again please include another side shot but with the full fork column. One other idea is to have the fork checked in a good fork guage, such as Park's. Odds are if the forks suffered a head-on the blades are not equally pushed back or could be off-center. Come to think of it I should have noted right off that no matter what you need to check the fork alignment.

I have seen this problem in the paint before anyways, way back in the mid 80s. Anyways i would check that out to the bare metal due to accident issues in near future.

Post your side on pictures in the C&V forum. I'm sure someone with that same bike or a similar contemporary model can comment on the shape of the forks.

The way that paint cracked says that paint lost adhesion in an uniform way on both sides - it suggests an impact as a most likely cause. To determine if it is in good condition; first strip it of paint, have it sand or media-blasted, then examine carefully the area of metal where the cracks were, if no damage is obvious, then try penetrants and dyes to look for micro-fractures, if all that is well, proceed to straigthen it (it will probably be ever so slightly bent), after straightening repeat dye testing for cracks, and if all is well, paint it again and ride. Lot of work, but if it were mine fork, I would not trust it without having all that carried out as a minimum of safety precaution. Also, if you can find someone who does it in your area, ultrasound examination could highlight possible fractures that may not show up on dye testing alone. As the fork already has some years on it, metal fatique is a real possibility.

I can't agree with the above, given that the deviation is so minor. I field straightened a fork on my Motobecane Grand Jubilee after it took a dump off a bike rack on top of a van, then rode 210 miles in 2 days on TOSRv and finished the job after I returned to the shop. I subsequently rode it on several criteriums (high speed, tight turns) and a loaded tour of 5000 miles without a problem. I also straightened forks and frames for racers who could not afford to just pitch a bike, turning down those where I had any doubts as to integrity.

In over 20 years of wrenching, providing support to tours, cat 3/4 racing and cross country riding I did not once see or hear of a fork with minor damage subsequently fail, before or after straightening. I'm open to hearing of contrary experiences from those who have professionally built or straightened frames, though.

Steel is a huge amount more forgiving than aluminium from the metal fatigue standpoint to the point where fatigue is not an issue in normal use. Even to bend and straighten steel it takes a lot of repetitive bendings past the elastic point to produce fatigue in the metal. IF that fork is actually bent it's not by much and straightening it back properly to maintain the oval section would not induce any significant weakening of the fork. Similarly a bend of such slight angle would certainly not cause any cracks in the steel to appear. One way or the other the cracks are only in the paint.

For all the armchair mechanics who can't give the OP a straight answer, here's something FYI: Colnago straight-blade forks taper at the rear ONLY. Front section of blade should be straight as an arrow:

Not my picture, not my bike:
http://i182.photobucket.com/albums/x300/garyf5354/Colnago%20Master%20Piu/DSC01107.jpg

I don't see any warp in the steerer tube, hence, the OP's fork is in need of a date with a Park FFS-1 for some minor cold-setting of the blades - no more. Unless the largest of those paint flakes are due to someone trying to run a Dremel through the steel (surface certainly looks like a simple rust mark as a result of the bare area created by the paint gap) there isn't any structural issues to worry about.

-Kurt

P.S.: If anyone wants to argue about the safety of cold-setting steel, go read this first: http://www.bikeforums.net/showthread.php?654093-How-many-of-you-ride-frames-and-or-forks-repaired-via-cold-setting

I can't agree with the above, given that the deviation is so minor. I field straightened a fork on my Motobecane Grand Jubilee after it took a dump off a bike rack on top of a van, then rode 210 miles in 2 days on TOSRv and finished the job after I returned to the shop. I subsequently rode it on several criteriums (high speed, tight turns) and a loaded tour of 5000 miles without a problem. I also straightened forks and frames for racers who could not afford to just pitch a bike, turning down those where I had any doubts as to integrity.

In over 20 years of wrenching, providing support to tours, cat 3/4 racing and cross country riding I did not once see or hear of a fork with minor damage subsequently fail, before or after straightening. I'm open to hearing of contrary experiences from those who have professionally built or straightened frames, though.

Fwiw, I professionally design, calculate, construct, manufacture and repair steel and composite structures for a living. So I said what I saw appropriate as I would do when I get a question to issue a repair estimate for a damaged steel structure. Minor or not, damage is there, as is the potential for failure. One example of a risky repair working right does not prove anything, as it is entirely possible for a sound structure to fail unexpectedly, then a damaged one has at least 10 times that risk. You might be comfortable having your fork fail, but saying that to others is simply not sound advice however you put it.

There are testing procedures, and standards, that serve to ensure proper and safe working conditions for any structure there is in use. So I said what is in my opinion, the bare minimum, for making sure that fork is ok for riding - and my opinion costs a lot when someone asks me professionally, because it is my no 1 priority the quality and safety of my work. You can never guarantee everything, but by having an sound, methodical, and uniform approach to solving problems, you can guarantee that most errors will be solved right in the beginning. In my time in this business, I've seen a lot of it - a lot of others who thought it is not necessary to follow regulations, standards, who did projects "by the feel of it". And generally, for them it all goes well, until that one project that fails catastrophically, but by then it's too late. And that one comes for them, sooner or later, but it always comes. And they are fast to ridicule strict following of the standards and regulations, they are fast to ridicule double checking everything, every calculation, until...they find themselves out of business because of their errors. Seen it more times then I can remember. I'm in no hurry when designing and working on something new, because I want it to be safe, to be quality, and to have it outlast it's design life. And working that way takes time. So take above advice about that fork fwiw. About the fork, is it probable that bending it back without checking would be trouble free? Probably. But there's always that little chance something may go wrong, and it may crack, and without testing it, you would not even have known it before it separates. Me, personally, would not ride that fork anytime again if I did not test it, and if I wasn't satisfied with test results. Fwiw.

I think the fork should be fine. I would strip the paint off just to be sure.

I also think the comment about the grease soaking through cracks are ignorant. I would perform a lobotomy just to be sure.

No argument that your procedures could definitively state the amount of damage and possibly the risk of rebending, but it seems overkill for this situation. I gave one personal example but you seemed to ignore the rest. I know of no logical reason that the steel used in this particular fork would suffer any significant harm from a minor rebending, and after over 20 years of repair and frame alignment experience yes, I am comfortable making that recommendation to someone else. Of course the OP should get a qualified in-person opinion.

As I said I'm open to anyone who actually has seen a negative consequence from a similar situation.

definitely stress cracks, probably means the fork is at least a little bent. judging by the paint, i'm guessing the fork has some miles on it. I would inspect very closely for cracks in the metal. Personally if someone came into my shop with that fork, I would suggest replacing it, but if it was mine, I would probably ride it as long as i was completely sure that there were no cracks in it

I think the fork should be fine. I would strip the paint off just to be sure.

I also think the comment about the grease soaking through cracks are ignorant. I would perform a lobotomy just to be sure.

Fine is one thing. Correct is another.

That said, unless the OP wants to get into a full-fledged restoration, there's no reason for him to have the fork cold-set, and leave it as-is.

-Kurt

Fwiw, I professionally design, calculate, construct, manufacture and repair steel and composite structures for a living. So I said what I saw appropriate as I would do when I get a question to issue a repair estimate for a damaged steel structure...

May I ask what you think of steel frames (not heat-treated) that have been straightened on a frame table?

-Kurt