routezab

Hi everyone
recently noticed this little crack on my cx frame, i wonder how serious is this thing and is it safe to use the frame?
unfortunately this is the only photo i have at this moment

skoda2

I wouldn't worry about it. The lug is brazed to the top tube and head tube and is not highly stressed, also the crack doesn't appear completely through the lug. Put a dab of auto body putty in the crack, sand it down, and touch-up with Testors model paint.
Cheers

sreten

Hi,

I have friend with serious cracks in his headtube. Everyone says it is toast.
He knows it is as as he can feel it riding the bike and he won't do certain
stuff he used to do on the bike. If it feels solid it probably still is, if it
doesn't then well of course it isn't, adjust riding style to suit safety.

rgds, sreten.

Interestingly (perhaps) I got involved when he was discussing some
some small cracks at the bottom of his head tube. I had a look and
had to be shown where this "bad crack" was, it didn't look too bad.

Anyway after perusing it over I turned round and said "you think
that's a crack, that is a crack", pointing at a huge (relatively) 1/2"
crack in the top of his headtube he had somehow not noticed.

FBinNY 

Odds are the head cup was pressed in without reaming the tube to the proper diameter. The head tube is under ring tension from the pressed in cup, and there's no reason to hope that the crack won't propagate.

OTOH, you're lucky this is the top cup, which is much more lightly stressed than the lower. I'd ignore it for now, because the remedy is the same now as later.

When/if it cracks to the edge, and you develop play in the top head cup (which may never happen) you'll have a choice of a good braze repair, or trying to skate by with bearing adhesive to stabilize the upper cup in the head tube.

You'll cross that bridge and deal with if/when you come to it, but there's nothing you can or should do now.

sreten

Hi FB,

I'm trying to understand the top fitting but I don't have the experience.

Is the first fitting above matched to just the lug and sits above the head tube,
or does it still fit the head tube with a wider flange for the extra lug width ?

I'm not sure what is holding what in place. I want to assume the head
tube extends flush with the top of the lug, but it might not, leaving
a recess for that first part, how is it usually done ?

rgds, sreten.

FBinNY 

Headset cups have sleeves and are press fitted into the head tube with an interference fit typically of 0.05mm. The tube is ductile and stretches to accommodate the sleeve. See the exploded view of a threaded headset here (2nd one down).

ksisler

OP; Recommend have a shop re-ream the socket in both the top and bottom of the headtube with the proper tool, face both ends while there, and then reinstall the headset. I have seen several headtubes cracked when the headset was pressed in without properly reaming of the headtube to fit the headset, as others have noted. Agree also with the other suggestion that if the bottom end is not cracked you can continue to use it with adequate safety despite a minor crack at the top. That is a good thing as repairing a cracked headtube would be quite expensive.
/K

Juha

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unterhausen

the OP should really take the fork and headset out and look to make sure the crack hasn't propagated further than just the lug. I am in the process of fixing a bike that had a huge crack in the head tube. I was questioning if it really was cracked when I first looked at it, but then when I looked harder, it was quite large. In fact, the entire outline of the lug was cracked.

This crack will continue to grow

TallRider

I'd recommend against removing the headset cup from the frame. If the crack is caused by pressure from the press-fit headset cup (as most people in this thread think), removal and reinsertion will cause a lot more stress to that lug than leaving it as-is.
Just ride it and keep an eye on it from time to time. It's not something that will fail catastrophically.
Your choice if you want to put in the money for braze repair somewhere down the line (if it needs it, which may never actually happen).

However, I have a sneaking suspicion that the crack is unrelated to the headset cup. The picture isn't very good so this is hard to tell, but the crack seems to be only on the exterior surface of the lug, and starts from the bottom of the lug, not from the top. So it may be unrelated and not a worry at all.
A better picture might give me a different opinion. Do you have a camera with macro (close-up focus) capability?

FBinNY 

+1, I didn't emphasize this enough in my first post. The process of removal and replacement may precipitate exactly what you're trying to avoid. Regardless of the cause or nature of this crack, or whether or not it will propagate, the repair will be the same now or later. So there's no benefit in exploring the situation, and you might as well ride the bike until the crack causes the upper cup to be loose (if it ever does).

sreten

Hi, Overanalysis. The obvious is the way it is. Stupid question.

rgds, sreten.