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Crown race

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Old 10-12-15, 06:57 PM
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markwesti 
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Crown race

Is there any difference between a 27 mm crown race as opposed to a 26.4 race in relationship to the bearing race it's self ? Do they use the same bearing race ? Thanks .
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Old 10-12-15, 09:22 PM
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The crown race uses an interference fit with the fork to be secure; a 27.0mm JIS crown race will not seat securely on a fork milled to use an 26.4mm ISO crown race, and a 26.4mm crown race will not even begin to seat on a fork milled to use a JIS 27.0mm crown race. So, if I understand your question, the answer is "no."
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Old 10-12-15, 09:46 PM
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Reading it as about the business end, ie. the ball track itself, then no, there's no difference for any given brand and model. Ie, a specific Shimano headset that's made in both ISO 26.4/30.2 & JIS 27.0/30.0 will be identical except for those fork/frame fir dimensions. The same is true of all headsets made both ways.
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Old 10-12-15, 09:52 PM
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In general, 26.4 mm and 27.0 mm crown races are identical for a given make & model of headset, with the exception of the diameter of the crown they seat on. If your fork's crown is 26.4 mm, use a 26.4 mm crown race. If the fork's crown is 27.0 mm, use a 27.0 mm crown race. The different diameters of crown race (again, for a given model) don't require different bearings or cups.

BUT... There are multiple standards for the diameter of frames' head tubes, just as there are for fork crowns. 30.2 mm is the common standard, but JIS headsets were designed for 30.0 mm tubes. If you're replacing a headset, measure the outside diameter of your fork crown and your old headset cups. Then be sure you buy a headset whose cups and crown race are the right size for your bike. (I've seen some odd combinations of ISO and JIS, so it's better to take a measurement than to make an assumption.)
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Old 10-12-15, 10:53 PM
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Thank's for the info guys . Prolly I should have said ... I bought a fork for my bike that has a 27mm dia. for the crown race (I don't have the fork yet It's in the mail) I was concerned that a 26.4 would maybe use a different dia bearing race . I'm not sure if that's the dia. on my bikes fork , as I got lazy and I did not check the fork on my bike . So any how .6mm how could they use a different race ? Sure they could I have a big pile of parts I thought would fit .
PS the dia. for a crown race ( 27 or 26.4 or whatever) is not milled , (I know that's always what is said .) It is turned .
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Old 10-12-15, 11:22 PM
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Originally Posted by markwesti View Post
....
PS the dia. for a crown race ( 27 or 26.4 or whatever) is not milled , (I know that's always what is said .) It is turned .
It takes a trained eye that knows how to read the scroll marks to know whether these are turned or milled. When we speak of milling a fork, we're talking about a holo-mill, or a cutter shaped like a ring, with teeth on the end. (see the one in use below).



Hollow milling is preferred in production because the job is done on a finished fork (after brazing and usually painting) for dimensional accuracy. Turning is also possible, but is a slower process and it's a pain to properly chuck the fork, and turn it with the blades whipping around in space.

Production hollow milling is done with a machine resembling a heavy duty drill press. The fork is clamped into a fixture which holds the steerer in line with the axis, and the spinning cutter is advanced, making the cut to a set depth. The entire process is done very quickly because there's no time lost to stopping a spinning fork as there would be with a turning operation.

In any case, I'm not sure which way you're going, but if you bought a 27.0 fork and own a 26.4 headset, it's a quick job to turn/mill the crown seat to 26.4. Any decently equipped mechanic can do it at a reasonable cost.
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Old 10-13-15, 06:30 AM
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FWIW...

I am in the same boat - purchasing a nice lugged 1" threadless fork from Japan which has JIS 27mm crown race seat.

Cane Creek's customer service said to order their standard EC30/26 headset which comes with 26.4mm crown race and then gave me the part number for a crown race which uses a 27mm seat on the fork. They said that the 27mm crown race will work with EC30/26 headeset, just use the 27mm one instead of the one that came with the headset and done. The extra 27mm crown race is $7.

The other option is to have the fork milled which is the way I might go. My thought is that headsets with 26.4mm crown race are more common and I'll have an easier time sourcing parts in the future.

Everyone says that a decent shop should be able to mill a fork but my experience is that it is more difficult than that. Maybe its just my dumb luck or the location (Atlanta) but it was a struggle to find a mechanic who understood what I was talking about, let alone able to do the work. One mechanic accused me of trying to jury rig parts together in a way they weren't designed to work. I finally found a shop owner in his 60's who used to build frames - he was like, "Yeah, I used to do that all the time. It's a little dusty but I still have the tool. Bring it." He wants $20 to cut it.

My understanding is that you can go either way - use a 27mm crown race or have the fork cut. Either way isn't very expensive.

The above is based on my research so trust but verify. I am open to correction.
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Old 10-13-15, 06:48 AM
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I just bough a Tange threaded headset, and the bike shop handed me a second race and said to return the one I didn't need
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Old 10-13-15, 08:09 AM
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Originally Posted by unterhausen View Post
I just bough a Tange threaded headset, and the bike shop handed me a second race and said to return the one I didn't need
One more reason to shop at your local LBS! I can't see a mail order/interweb "store" sending a second race. Then, of course, the chance of the buyer shipping back the un needed one is even less. Andy.
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Old 10-13-15, 10:05 AM
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FB , thank you for taking the time to type that up . That was certainly a learning experience for me . Also thanks for the reply's guys . Mark .
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Old 10-13-15, 10:16 AM
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Originally Posted by FBinNY View Post
It takes a trained eye that knows how to read the scroll marks to know whether these are turned or milled. When we speak of milling a fork, we're talking about a holo-mill, or a cutter shaped like a ring, with teeth on the end. (see the one in use below).



Hollow milling is preferred in production because the job is done on a finished fork (after brazing and usually painting) for dimensional accuracy. Turning is also possible, but is a slower process and it's a pain to properly chuck the fork, and turn it with the blades whipping around in space.

Production hollow milling is done with a machine resembling a heavy duty drill press. The fork is clamped into a fixture which holds the steerer in line with the axis, and the spinning cutter is advanced, making the cut to a set depth. The entire process is done very quickly because there's no time lost to stopping a spinning fork as there would be with a turning operation.

In any case, I'm not sure which way you're going, but if you bought a 27.0 fork and own a 26.4 headset, it's a quick job to turn/mill the crown seat to 26.4. Any decently equipped mechanic can do it at a reasonable cost.
+ 1. I've done this a few times with a 100% success rate.
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Old 10-13-15, 01:13 PM
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I found this very interesting .
https://www.youtube.com/watch?v=9lI9-wyrub
here is another one .
https://www.youtube.com/watch?v=RtWlu2azWtc

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