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Headset Standard for Dawes Imperial

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Headset Standard for Dawes Imperial

Old 09-05-17, 04:20 PM
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wilkyboy
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Headset Standard for Dawes Imperial

Does anyone know here what on earth the threaded headset on an old '84 Dawes Imperial is spec'd to?

I got a BBB BHP-15 spec'd to 1" ISO (the rest of the bike was ISO so I assumed the same for the headset), but the crown race just would not go on - I then measured it, the fork is 1 1/6" (~26.9 mm) and the crown race was 26.4 mm, but alarm bells should have been ringing when the cups just would not go in the frame.

ISO cups are 30.2mm, JIS are 30.0mm.

Also, the old crown race measured 27.5mm (it fell off the fork when I turned it upside down ). Now I have no idea what's going on as Sheldon Brown's guide to threaded headset sizes contains nothing that has a 27.5mm crown race diameter.

Is it JIS or should it be ISO? Or am I completely wrong and should it be something else entirely?
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Old 09-05-17, 06:41 PM
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No idea why your headset is as goofy as you describe, but it would be quite trivial to mill your current fork crown race seat to fit an ISO 26.4mm crown race. Since the head tube is already ISO spec, you'd then be able to use any ISO spec threaded headset.
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Old 09-21-17, 03:23 AM
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ZG862
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Original headset was a Tange Levin LV-1500 as far as I can establish. Trying to source one of these myself!

Z
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Old 09-24-17, 08:02 AM
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Originally Posted by ZG862 View Post
Original headset was a Tange Levin LV-1500 as far as I can establish. Trying to source one of these myself!

Z
Yup - that's exactly what's fitted to mine ...
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Old 09-28-17, 07:09 AM
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Any pictures of the headset that came off? I'm wondering whether this may have contributed to the problems you're experiencing. Seems unlikely though - I can't imaging how a headset could make the head tube shrink.

Z
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Old 09-28-17, 08:27 AM
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Sounds like your Dawes needs a JIS headset. The crown race should be 27.0mm, which sounds about right if the old 27.5mm one is loose, but your new 26.4mm race is way too tight. As for the cups, JIS calls for 30.0mm, vs the larger 30.2mm for ISO cups. Usually, this is a small enough difference that you can just force the ISO cups into a JIS frame, especially if they are alloy cups.

Back in the day, most of the Tange headsets were JIS. Now, most of them are ISO, but maddeningly, their JIS options use the larger 30.2mm cups. There are few if any true JIS headsets being produced currently.

If you can't source a JIS headset, it's a pretty simple operation to mill the fork crown, and ream the head tube for ISO spec parts. Probably 30-45 minute job for a shop with the proper tools.
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Old 09-28-17, 09:26 AM
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Good call Mr Murphy.
It does mean that I'm going to have to take the nasty steel headset off my soon-to-be-repainted frame to check its size before I press the button on a LV-1500 I have lined up of course. But that could save a world of pain, so thanks!

Z
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Old 09-28-17, 10:08 AM
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Hmm. That was interesting.
Crown race dropped straight off mine too.
Measures up at a healthy 26.9 at the crown, 29.9 in the head tube. Sounds very JIS to me...

Z
PS/ And the current LV-1500 does seem to be ISO. That's added a task to the list for the frame shop.

Last edited by ZG862; 09-28-17 at 10:11 AM.
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