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Headset cups taper before meeting head tube, leaving a gap.

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Headset cups taper before meeting head tube, leaving a gap.

Old 06-15-13, 11:15 PM
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slopvehicle
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Headset cups taper before meeting head tube, leaving a gap.

I'm putting a Crank Bros. Cobalt C directset onto my 29er frame (2011 Soul Cycles Dillinger) to work around a fork with a short steerer tube. All indications are that the directset is compatible with regular style 1 1/8" head tubes, but when I lined it up, ready to press, I noticed that the bearing cups taper on the outside a little before the smaller flange (the part that gets inserted) begins.

This looks weird-- that taper will leave a little bit of the face of my head tube exposed. I guess this frame has a slightly oversize head tube? No pics of the installed directset I could find on the internet showed a situation like this...everyone's frame seems to have a smaller outer diameter head tube!

Anyhow, will this thing be reasonably safe once I press it?

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Last edited by slopvehicle; 06-15-13 at 11:19 PM. Reason: clarifyin'
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Old 06-16-13, 01:05 AM
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Functionally, not a problem. The gap is aestethics only. If you want to get picky about it, you could try finding a thin o-ring, or just applying some black caulk/silicone tofill the gap and make it less obvious.
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Old 06-16-13, 02:08 AM
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Cool, thanks for the reply. Functionality's the game here-- got an older Reba inherited from my old Karate Monkey, and the KM's headtube was shorter, so I'm trying to avoid having to drop $500+ on a new fork. As it is, I had about 35mm of steerer with a Cane Creek S3, which severely limited my choice of stems. The new headset should give me an additional 7mm to play with.

Just pressed it and it went a little rough but I guess that's the story on these headsets-- supposedly they're a hair wider than usual. Got it seated in the end, thankfully.
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Old 06-16-13, 04:35 PM
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Originally Posted by dabac View Post
Functionally, not a problem. The gap is aestethics only. If you want to get picky about it, you could try finding a thin o-ring, or just applying some black caulk/silicone tofill the gap and make it less obvious.
Of course, it's a matter of degree, but headset cups need to be pressed to the bottom. Otherwise the pressure of the preload, combined with road shock will continue to settle the cups deeper. This isn't a real problem if the head tube was reamed to spec. and the press-in part of the cups are within tolerance. The only issue there is that it's a PIA, since you'll be readjusting the headset to take up the slack until it's finally home.

OTOH, if the parts are out of spec, one of three things may happen.

1- the cup "bottoms" on the oversize section and settles there and all is OK.
2- the cup continues to get pressed in by the load, distorting the head tube, so that possibly the next headset is sloppy, or is jammed in so tight that it's difficult to remove (or both).
3- the cup rides high (as pictured) and the headset fails. This is because headsets aren't designed to carry the load via the pressed in portion (sleeve). Pressure on the improperly supported bearing area can lead to cracking between it and the sleeve. This is more likely if the lower cup isn't seated, but the upper isn't loaded as much and rarely cracks that way.

There's no way to see exactly what's happening from the photos, but among the possibilities are that the head tube wasn't reamed to spec, the Head tube was reamed, but not to enough depth for the sleeve, or the headset itself is out of spec.

The OP can take his chances, but this is clearly not seated properly, and if it were me, I'd pop out the headset and find out why it isn't fitting to the bottom as it should.
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Old 06-17-13, 03:53 AM
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Originally Posted by FBinNY View Post
Of course, it's a matter of degree, but headset cups need to be pressed to the bottom. Otherwise the pressure of the preload, combined with road shock will continue to settle the cups deeper. This isn't a real problem if the head tube was reamed to spec. and the press-in part of the cups are within tolerance. The only issue there is that it's a PIA, since you'll be readjusting the headset to take up the slack until it's finally home.

OTOH, if the parts are out of spec, one of three things may happen.

1- the cup "bottoms" on the oversize section and settles there and all is OK.
2- the cup continues to get pressed in by the load, distorting the head tube, so that possibly the next headset is sloppy, or is jammed in so tight that it's difficult to remove (or both).
3- the cup rides high (as pictured) and the headset fails. This is because headsets aren't designed to carry the load via the pressed in portion (sleeve). Pressure on the improperly supported bearing area can lead to cracking between it and the sleeve. This is more likely if the lower cup isn't seated, but the upper isn't loaded as much and rarely cracks that way.

There's no way to see exactly what's happening from the photos, but among the possibilities are that the head tube wasn't reamed to spec, the Head tube was reamed, but not to enough depth for the sleeve, or the headset itself is out of spec.

The OP can take his chances, but this is clearly not seated properly, and if it were me, I'd pop out the headset and find out why it isn't fitting to the bottom as it should.
I think you may be mistaken about the problem. My understanding of what the OP wrote is that the cup is designed with a slight taper or chamfer and does not cover the entire surface/face of the headtube which will leave a ring of headtube face exposed around the outer circumfrence of the headset cup(s). This should not cause any problems functionally.

I could have misread the OP as well so you may be correct.
-j
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Old 06-17-13, 04:12 AM
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OP hasn't finished installing it in the pic:

Originally Posted by slopvehicle View Post
Anyhow, will this thing be reasonably safe once I press it?
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Old 06-17-13, 08:42 AM
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Originally Posted by Greenfieldja View Post
I think you may be mistaken about the problem. My understanding of what the OP wrote is that the cup is designed with a slight taper or chamfer and does not cover the entire surface/face of the headtube which will leave a ring of headtube face exposed around the outer circumfrence of the headset cup(s). This should not cause any problems functionally.

I could have misread the OP as well so you may be correct.
-j
I read it and was influenced by the photo, which shows the cup only partly pressed in. Rereading it, and looking more closely at the photo, I agree that he's likely talking about the OD chamfer on the head cup which is of no consequence.

A drop of touchup paint or a smear of stiff grease to cover the exposed bare metal on the face of the head tube is all that's needed.
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