fitting headset cups to an oversized head tube
08-28-15, 07:16 AM
#1
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fitting headset cups to an oversized head tube
1. What I know:
The frame in question is a 1984 Univega Alpina Pro, which is a TIG welded chrome-moly MTB frame. Like many early MTB's it has some BMX features; for example, it takes a 21.15 mm quill stem.
The fork has a 1" threaded steerer with a 27.0 crown race.
I measure the internal diameter of the head tube at 32 mm, so I presume 1 1/4" (31.8 mm).
1" threaded headset cups are made to fit into a tube with internal diameter of either 1 3/16" ID (30.2 mm) or 30.0 mm. (see Sheldon Brown)
What I want, obviously, is a something that reduces the head tube diameter from 1 1/4" to 1 3/16".
Wheels Mfg makes a "head tube reducer" such as this 1-1/8" To 1" Bmx Headtube Reducer, which "Reduces headtube ID from 34mm to 30.2mm" and this 1-1/4" To 1-1/8" reducer, for which I can't find metric specifications.
2. What I don't understand:
How do we interpret the Wheels Manufacturing specificiations? 1 1/8" is not 34 mm, and 1" is not 30.2. I understand some dimensions are nominal. Should I order one of the parts linked? Or should I just make myself a shim from some sheet steel?
The frame in question is a 1984 Univega Alpina Pro, which is a TIG welded chrome-moly MTB frame. Like many early MTB's it has some BMX features; for example, it takes a 21.15 mm quill stem.
The fork has a 1" threaded steerer with a 27.0 crown race.
I measure the internal diameter of the head tube at 32 mm, so I presume 1 1/4" (31.8 mm).
1" threaded headset cups are made to fit into a tube with internal diameter of either 1 3/16" ID (30.2 mm) or 30.0 mm. (see Sheldon Brown)
What I want, obviously, is a something that reduces the head tube diameter from 1 1/4" to 1 3/16".
Wheels Mfg makes a "head tube reducer" such as this 1-1/8" To 1" Bmx Headtube Reducer, which "Reduces headtube ID from 34mm to 30.2mm" and this 1-1/4" To 1-1/8" reducer, for which I can't find metric specifications.
2. What I don't understand:
How do we interpret the Wheels Manufacturing specificiations? 1 1/8" is not 34 mm, and 1" is not 30.2. I understand some dimensions are nominal. Should I order one of the parts linked? Or should I just make myself a shim from some sheet steel?
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Last edited by rhm; 08-28-15 at 07:19 AM.
08-28-15, 10:10 AM
#2
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You're confusing fit dimensions for pressed in cups with nominal or actual headset dimensions.
A 1" headset needs a headtube ID of 30.0 or 30.2mm and a 1-1/8" headset needs 34mm.
Those don't correspond to the headset size because headsets are sized by the fork they fit on. The head tube ID has to be larger because you need room between the fork and the headtube for the pressed in part of the headset, plus clearance for the fork to turn.
Now 32mm doesn't correspond to any standard. I suspect you're mismeasuring a 30.2 head tube, possibly because it's ovalized. But if not, you might need to do some creative shimming or build up the ID another way.
Start by going to a local bike co-op (if any) and seeing how a 30.2 cup fits. If it does you're done, if it's still sloppy then there are fixes, but they depend on exactly how much shimming is needed, and more important why.
I hope this gives you a starting place to asses your situation.
A 1" headset needs a headtube ID of 30.0 or 30.2mm and a 1-1/8" headset needs 34mm.
Those don't correspond to the headset size because headsets are sized by the fork they fit on. The head tube ID has to be larger because you need room between the fork and the headtube for the pressed in part of the headset, plus clearance for the fork to turn.
Now 32mm doesn't correspond to any standard. I suspect you're mismeasuring a 30.2 head tube, possibly because it's ovalized. But if not, you might need to do some creative shimming or build up the ID another way.
Start by going to a local bike co-op (if any) and seeing how a 30.2 cup fits. If it does you're done, if it's still sloppy then there are fixes, but they depend on exactly how much shimming is needed, and more important why.
I hope this gives you a starting place to asses your situation.
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FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
08-28-15, 10:18 AM
#3
Constant tinkerer
Edit: after reviewing Sheldon Brown's page on headsets and the post below, if you actually have a 32.7mm headtube ID (that's the dimension listed in Sheldon's page) then the advice below is spot on.
https://sheldonbrown.com/headsets.html
If it were my bike and I didn't have or didn't care about using the original fork I'd look at the thickness of the headtube and see about reaming it out to take a standard 1 1/8" headset. You'd only need to increase the ID by 1.3mm which means you're only removing 0.65mm of material on the inside surfaces. Then you could use any standard 1 1/8" threadless fork.
https://sheldonbrown.com/headsets.html
If it were my bike and I didn't have or didn't care about using the original fork I'd look at the thickness of the headtube and see about reaming it out to take a standard 1 1/8" headset. You'd only need to increase the ID by 1.3mm which means you're only removing 0.65mm of material on the inside surfaces. Then you could use any standard 1 1/8" threadless fork.
Last edited by FastJake; 08-28-15 at 11:50 AM.
08-28-15, 11:36 AM
#4
Calamari Marionette Ph.D
Old school BMX bikes, many old MTBs and old electroforged Schwinns (most OPC bikes) had an odd size head tube ID for their 1" forks. The cups are 32.5mm and I highly suspect this is what you need. Especially when noting the 21.1 quill.
The good news is they are still available in cheaper steel with retainer ball bearings or snazzy aluminum with cartridge bearings. Lots of colors to choose from and your choice of 27 or 26.4 crown race.
I have one of each version and they are very good quality.
1" Threaded Headset Bicycle BMX parts old school BMX
The good news is they are still available in cheaper steel with retainer ball bearings or snazzy aluminum with cartridge bearings. Lots of colors to choose from and your choice of 27 or 26.4 crown race.
I have one of each version and they are very good quality.
1" Threaded Headset Bicycle BMX parts old school BMX
Last edited by SquidPuppet; 08-28-15 at 11:50 AM.
08-28-15, 01:13 PM
#5
multimodal commuter
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Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
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You're confusing fit dimensions for pressed in cups with nominal or actual headset dimensions.
A 1" headset needs a headtube ID of 30.0 or 30.2mm and a 1-1/8" headset needs 34mm.
Those don't correspond to the headset size because headsets are sized by the fork they fit on. The head tube ID has to be larger because you need room between the fork and the headtube for the pressed in part of the headset, plus clearance for the fork to turn.
Now 32mm doesn't correspond to any standard. I suspect you're mismeasuring a 30.2 head tube, possibly because it's ovalized. But if not, you might need to do some creative shimming or build up the ID another way.
Start by going to a local bike co-op (if any) and seeing how a 30.2 cup fits. If it does you're done, if it's still sloppy then there are fixes, but they depend on exactly how much shimming is needed, and more important why.
I hope this gives you a starting place to asses your situation.
A 1" headset needs a headtube ID of 30.0 or 30.2mm and a 1-1/8" headset needs 34mm.
Those don't correspond to the headset size because headsets are sized by the fork they fit on. The head tube ID has to be larger because you need room between the fork and the headtube for the pressed in part of the headset, plus clearance for the fork to turn.
Now 32mm doesn't correspond to any standard. I suspect you're mismeasuring a 30.2 head tube, possibly because it's ovalized. But if not, you might need to do some creative shimming or build up the ID another way.
Start by going to a local bike co-op (if any) and seeing how a 30.2 cup fits. If it does you're done, if it's still sloppy then there are fixes, but they depend on exactly how much shimming is needed, and more important why.
I hope this gives you a starting place to asses your situation.
Seriously funny stuff there!Thank you, @SquidPuppet, I believe you nailed it.
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Last edited by rhm; 08-28-15 at 10:22 PM.
08-29-15, 06:17 AM
#6
Keener splendor
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