MarkUK82

Need some advice and help.
My steering tube fits crown races ( ISO 26.4 ). I purchased a Dura-Ace 7600 headset. Before I purchased the item I was told it was ISO 26.4.. Installed the headset today and the crown race is pretty loose. About a 1mm gap. Im guessing it JIS and not ISO.
My question is.. is there anything that I can do to make it work? Could I just get a 26.4 ISO crown race? would that work with my JIS headset?

Also. Since this is probably a JIS headset and my bike was designed for ISO. Would the dura ace 7600 Upper and lower headset tube races actually fit into my headtube?

thanks!!

dedhed

Time to measure things to verify.

fietsbob

And you may mix & match the fork crown race, if necessary..

Personal Measurement is good, got a digital caliper?

HillRider

If your frame is really ISO dimensioned, the JIS cups (30.0 mm) will be a loose fit in the ISO headtube (30.2 mm). Basically, you bought the wrong headset.

Asi

Time for shims (JK - hard to do but theoretically possible and practically is possible with a precision lathe, skills and time to spare)

Return it and buy the proper headset (or replace the frame, whichever is cheaper to do)

Measure twice and order once.

Kontact 

Agree that you need to measure before you assume - your fork may be undersized and the 7600 headset is 26.4. Find out, first.

Dave Mayer

Yeah, this is common now: i'd guess about half of the remaining quality vintage headsets in shop inventory are useless orphaned JIS units. And the shop staffers don't know the difference.

Return it.

bikemig 

This is useful (along with a set of vernier calipers):

https://www.sheldonbrown.com/cribsheet-headsets.html

Ghrumpy

Except it's flat wrong about so-called ISO headsets, as well as Professional. There is no such ISO dimensional standard. ISO refers to a thread form, not a crown race diameter.

Headset dimensions and standards can be confusing because there are several dimensions that don't have anything to do with each other directly. The threading, if there is any, doesn't care what the cup skirt diameter is, and neither care what the crown race diameter is. So thread standards and dimensional standards don't necessarily correspond unless the standard explicitly mandates it.

The word "standard" is also problematic, because some standards are thus because a standardizing body has said so. Other standards are thus because some company has made all their products to their own proprietary dimensions. Some standards are thus because if some corporate standard becomes the market leader, other companies follow suit, making it a de facto standard.

What Sheldon's site calls out as an ISO headset is actually a "Professional" standard aka Campagnolo, and what Park Tools calls "Modern European" (as contrasted with "Vintage European.") Professional standard headsets are not thread-specific. Campagnolo and many others made headsets for decades with the same cup and race dimensional standards, but with different threads (BSC, Italian, and French.) French thread headsets are still manufactured by a few companies.

As noted, the ISO standard refers only to the thread form on the steerer tube (1.375" x 24 tpi.) Sutherland's indicates that a 30.0mm cup skirt is also part of the standard, but no crown race diameter is mentioned. I have not seen the actual text of the relevant standard though, so it's possible that has changed. In any case, Sheldon's site is still wrong about both the ISO and Professional standards, in that his categorization contradicts both other references and reality.

The ONLY 1" headset standard that specifies both cup and race dimensions AND threading is JIS: 30.0mm cup skirt OD, 27.0mm crown race ID, 1.370" x 24 tpi BSC thread form (functionally interchangeable with ISO thread.)

Even if the cup and race diameters are the same spec, an Italian or French thread (25 x 1mm) headset cannot logically be JIS . It just so happens, however, that many such headsets share the same cup and race diameters as JIS. But they are older than JIS.

It is best to understand and specify actual cup and race dimensions and thread forms separately than to attempt to rely on a "standard" that may or may not exist. I understand the desire to shorthand this tiny additional level of complication, but given the number of errors that can and clearly do arise from that, it's worth the small amount of extra effort. It's not that hard.

Kontact 

Given the amount of explanation required and the fact that many other non-thread standards are simply "ISO", you've certainly made it sound hard.

It isn't that you're wrong, but you would have an awful hard time finding a 1" headset that is not JIS yet has 27.0 crown race.

bikemig 

Right, it happens but not often. Most of the time, the specs given on Brown's webpage works. I have a bike--a custom built Mike Melton--that mixes the two standards but that's the only time I've seen it.

Bike Gremlin

This might help (works for me).

03) Bicycle headset bearings standards - SHIS - Bike Gremlin

Kontact 

Well, that wasn't very nice of him.

bikemig 

Custom Melton road bike
Well he didn't make the bike for me, . I bought it new from a shop where it was hanging in the early 80s. So I didn't take it personally when I measured out the headset and realized that it was not going to be easy to find a replacement . . . .

Andrew R Stewart 

I agree that headsets are an area of dimensional variety. Today at work we had a customer who brought in his new, yet to be ridden, modern BMX track bike complete with carbon fork. maybe about 17 lbs! The bike was sent (problem #1 ) with the wrong headset, or missing parts, we didn't have time to do the full assessment on the spot. He was convinced that all he needed to know was the 1 1/8" spec. When we showed him the various choices that existed he reverted to that 1 1/8" spec and didn't seem to understand that all that dimension referred to was the steerer OD and nothing else, like the cups. As he wasn't good with leaving it we never actually pulled it apart and measured/determined the real specs.

One more customer who thinks there's too many details to know about to be bothered about (problem #2 ). We are just suppose to know about his custom bike's spec in a greater detail then the published spec sheet says, right now so he can still race tonight (problem #3 ).

Maybe 30 years ago I could tell by just looking at a headtube or measuring just the crown race to know which standard was used. But no longer. Andy

JohnDThompson 

In a case like this, where the frame is prepped to one specification but the fork crown race seat is prepped to the other specification, I'd just re-do whichever part isn't ISO spec to accept ISO spec.

bikemig 

Sure but I don't have tools like that and a lot of shops don't anymore either. It was a lot cheaper and easier to buy a headset from Velo orange as they let you switch out the crown race.

Kontact 

If your shop doesn't have the tool, try a different one. These tools don't wear out and aren't going away anytime soon - some shop inherited them from some previous incarnation.

Ghrumpy

Nope. Almost all the ISO standards are ONLY threading. Spoke nipple flats and BB taper are the only non-thread ISO standards that anyone cares about that I can think of off the top of my head.

The explanation isn't "required." I only offered it to give background. Allow me to cut to the chase: The Sheldon Brown web site is incorrect. ISO specification for headsets correctly refers only to threading (and if it does spec a cup skirt diameter, it's 30.0mm.) "Standard" might not mean what you think it means. So measure your parts and the corresponding frame interfaces and make sure they are compatible.
Simple. We measure seatposts and stem clamps/handlebars. What's so hard about measuring headsets? BTW, the SHIS system (thx @Slaninar) doesn't mention "standards," only measurements.

WRT to the mistaken ISO/JIS headset dichotomy, this appears to follow the same assumption that plagues BB taper discussions, which is that there are only these two standards. It's simply not so, not even in current production.

In current production, yes. In pre-1990 production, no, because there was no such thing as JIS at all.
To reiterate, these "standards" are voluntary. It's a mistaken assumption that headset dimensions, even in current production, must adhere to one "standard" or another.

WRT that, @JohnDThompson, frames are prepped to a dimension, which is not necessarily a specification or a standard. There were many many pre-1990 headsets made to dimensions that do not follow any modern so-called standard. Of which, allow me to repeat, only one is a dimensional AND a thread standard, and it's NOT "ISO". It's JIS.

Kontact 

Here's a 1983 Shimano catalog page that refers to JIS headset dimensions by name for thread, races and cups:
Shimano 600 EX catalog (11-1983)

Kontact 

Reading more about this, I downloaded the Campagnolo 1988 dealer catalog;

VeloBase.com - Catalog Scans

What I think is interesting is that Campy offered French, Italian or BSC threaded headsets, but only have one part from the crown race and upper cone and lower cup. So by 1988, Campy considered the 26.4 crown and 30.2 cup/cone to be "standard" for European bikes. (Campy didn't make JIS anything).

So whether there is an "ISO" designation or not, there does seem to be a kind of de facto agreement in the '80s that bikes used the same dimensions for headsets with the exception of threading.


And probably because all frame were going to be prepped with something like a standard Campy tool kit, which makes the headtubes and crown diameters uniformly 30.2/26.4. Those dimensions don't really come from the tube supplier but the cutting tools.