jkimballcook

How can I make sure my new JIS threaded headset will fit before trying to install it so I don't damage my headtube?

I'm rebuilding my old late 80s centurion dave scott ironman expert. (See thread in C&V here https://www.bikeforums.net/showthread...Expert-Rebuild). In the process of stripping it all down for a new powdercoat job, I discovered that the headset was shot (I basically knew this before stripping because of the "indexed" steering, but pulling it all out and inspecting it just confirmed it. The old headset was a shimano 105. From what I could tell searching online, centurions of that vintage all used the JIS standard for headset sizes.

I ordered a new tange levin JIS headset, and it came yesterday. Comparing the new headset to the old, the crown race (27mm) looks identical, which seems to confirm that I was right to go with JIS. But the head tube races (30.2mm) don't fit as far into the head tube as the old races do. (I haven't tried to press them in yet, just dry-fitting them to see how they compare to the old one.) I don't have a caliper, but using a metric ruler, I measure the headtube inside diameter at 30mm.

So my question is, with the race being about .2mm wider than the ID of the headtube, will I damage the head tube if I try to press them in as is, or do I need to get the headtube reamed?

I'm not sure why the new races would be bigger than the old ones. Maybe the old ones are just compressed from being pressed in before? Maybe I should just try to press the new ones in, but I don't want to damage and possible trash this frame, so I'd like to be sure before I start trying to apply force. Any help or advice would really be appreciated. Thanks.

jkimballcook

57 views and no replies. This must be a really weird problem. Too bad.

Anyway, here's an update:

I got a hold of some calipers yesterday, and sure enough, my old headset was a full JIS (27.0mm crown race, 30.0mm cups), and the ID on the headtube is 30.0mm. Sheldon says 30.2mm cups and 30.0mm cups all fit in the same size headtube (https://sheldonbrown.com/cribsheet-headsets.html), and Park says a 30.0mm headtube can take 30.2mm cups (https://www.parktool.com/blog/repair-...dset-standards), but I spoke with three different LBS's who all said they thought 30.2mm in a 30.0 tube is too big. I also took it over to a friend of mine who is a mechanical wizard with automotive stuff and dabbles in bikes, and he said that he would be worried about damaging or deforming the headtube trying to press fit something with that big of a difference.

So I figured I need to just find a headset with 30.0mm cups. There are a few full JIS headsets out there with 30.2mm cups, like the velo orange, but the problem is that none have a small enough stack height to work with my fork. The velo orange is pretty typical with 38.5 stack height. But the original centurion fork has an unusually low maximum stack height of 32mm (which, now that I realize, is too small even for the tange levin I bought, so even if I could figure out the cup size problem, I still couldn't use it). The tange passage has a low enough stack height, but only comes with "standard 1" headset cups," which I take to mean 30.2mm (ISO) cups. I found two NOS 105 headsets on ebay that look like they would work, but I'm not excited about spending $50 or 80 for an old 105 headset. (Also, the NOS 105 is a grey resin on the outside, which is fine, but I really like the chrome, especially with the blue powdercoat; not that big of a deal, but if I'm paying $80 for a headset, I'd like to be excited about it).

At this point, I'm thinking my best option is to get the headtube reamed and the fork crown milled to ISO and forget about all this JIS headache. If I got the NOS 105, and just had to replace it again in a few years when old 105 stuff is even more rare than now, that's not an attractive proposition. The couple of shops I spoke with did not like that idea of reaming the headtube, saying that they worry it would weaken the frame. But given that it's a lugged frame, there's more material to work with at the top and bottom of the headtube than otherwise, and I would only need it reamed at the top and bottom where the cups press in, so only the lugs would be reamed, not the thinner tube itself, right? I don't think I mentioned on the phone that it was a lugged frame, so maybe that would make them feel a little better about milling the headtube if I brought it in and they could look at it.

Anyone have any helpful ideas?

fietsbob

There you go, a digital caliper will let you measure, with some accuracy,
the crown race seat and head tube ID.

Pro LBS should have a ream and face/ die set
to recut overlarge fork crown seats,
and undersize Head tube ID's.

Older Italian Steel frames, Famous names, shipped painted,
but expected each dealer to have the tools
to finish the thread cutting , chasing,
facing and reaming to assemble the bike.

HillRider

Converting JIS frames/forks to ISO was a common procedure years ago and i'm surprised your LBS is reluctant to do it unless it's a new shop with no knowledge of older bikes. I had my '85 Bridgestone 400 modified when the OEM Tange headset wore out in about 10,000 miles and it's still on the road.

jkimballcook

One LBS is saying $40-50 to ream the tube and another $40 to mill the fork crown. Way excessive, no? The other LBS is saying he can do the fork crown but isn't sure he can do the headtube because he doesn't have the right taps. I'm thinking at this point of leaving the crown race as is and either (1) finding a machine shop to do the head tube or (2) doing it myself, using my friend's tools. It only needs to be .1mm bigger inner diameter, I would think somebody could do that.

HillRider

Yeah, that seem quite high. IIRC, my LBS milled the fork crown but just pressed in the cups with no other preparations.

FBinNY 

If your frame is still JIS, H/T ID just under 30.0mm, you have two choices for a proper job.

get a true JIS headset that will work, and I can help you there, as I have some nice Low stack JIS (27/30mm) SunTour Superbe Pro track headsets (very old stock), which should meet your needs.

Or have the head tube properly reamed to ISO 30.2mm (+0.0 -0.05), by a decent shop. This shouldn't be expensive and will give you access to a wider selection of headsets going forward. While you're at it, also have the fork crown hollow milled to 26.4, so you don't have to hybridize headsets.

As to whether a 30.2 cup can be pressed into a 30.0 frame, the answer is maybe. Steel is very ductile, and if the frame is a typical welded frame with a thin headtube and no ring at the bottom, it'll probably be OK. But on a lugged frame the added wall thickness will make the frame too stiff and the pressing load excessive, possibly cracking he headset cup (especially if it's aluminum). For carbon frames it's definitely impossible and will crack the frame, and aluminum and Ti are in between and will either crack or give depending on the temper (something you're not equiped to measure).

With respect to Park and anyone saying flat out that it's OK to press a .2mm oversize cup into a frame, they're just plain wrong. The correct level of interference is .05mm, based on a steel lugged frame with a wall thickness of 2-3mm. For steel without the band, or aluminum up to about 3mm, Ti up to 2mm you would want more interference to compensate for the weaker (stretchier) tube, so maybe up to .1mm, but .2mm well above standard specs.

HillRider

Unless you can get both the headtube and crown race milled reasonably AND find a suitably short stack height headset, I'd take FBinNY up on the Sun Tour heasdets. Sun Tour made very good components and if you are concerned about the future, buy two.

Your need for a short stack height is going to be a problem. As you saw, even the Tange is too tall and short stack headsets are rare in either JIS or ISO. Chris King's GripNut headset can be made to have a stack height of as low as 33.0 mm but it's ISO only and VERY expensive. I had the same stack height problem on a '92 Trek 1420 and "solved" it by replacing the fork.

ultraman6970

my opinion ok? they send you an ISO or and Italian headset not a jis. Shimano used to sell iso/italian headsets, Shimano had crownraces to mix and match stuff also so who knows what you got in there, sure the guys just measured the crown race and thats it.

As for the 30.2 in 30?? yes it will fit. Just put A LOT of grease and go really really SLOW. As long you dont start taking the headset out each week nothing will happen to the frame.

Second option? Just get some sand paper and sand the headset cup a tiny bit, or a file but go really slow so you dont take too much material, i would do this just to be conservative, it works just fine just put a lot of grease in there when installing the cups.

3rd option, tell the LBS to ream the front tube to 30.2, I imagine somebody should have the tools?? Is like 10 mins of their time, maybe like 100 bucks of your pocket if they like to steal costumers.

Good luck

jkimballcook

Lot's of really good info. Thanks to everyone. Very helpful.

FBinNY: I'll PM you about one of those NOS suntours. By the way, yours is the best explanation I've heard yet on the interference issue, and you've convinced me that it is definitely a bad idea to try to press it in. It might work, as others have noted, but if I can get the right size cups, or if I can get the machining done, why risk damaging this great old frame that I like so much and just spent $150 getting powdercoated?

In my search for somebody who could do the machining I found a one-man LBS near my office that says he can special order a tange passage (30.4 stack height) in a 27/30mm for like $15. Maybe I'll stop by his shop this afternoon and see if that pans out.

Also, I found another LBS that says they'll mill both the headtube and crown race seat to ISO for $30. That seems more reasonable.

So there's two good options.

FBinNY 

$30-40 sounds about right for the frame prep work, and might make sense especially if the painter got lots of paint into the headtube. As I wrote earlier, don't do the frame and not the fork, otherwise you'll be hybridizing headsets forever.

The $15.00 headset is a good deal, My Spb Pro model is about triple that.

jkimballcook

FBinNY: Yeah, $30 sounded more within reason, but to your point about paint, there is no paint anywhere inside the headtube, it is completely clean. The frame is freshly powdercoated and the powdercoater blasted and cleaned the frame inside and out and did a really nice job keeping the powder off of threads and out of the inside of the tubes (except for a tiny bit at the bottom inside of the BB shell, but that's not really an issue because it's only in the middle where there are no threads--I imagine it's probably just a few grains of powder that fell down the seat tube).

jkimballcook

Just an update. I stopped by the new LBS on Friday and ordered the tange passage with the correct cup diameter, crown race diameter, and sufficiently low stack height. The guy at the shop was really nice and helpful. It's just a one-man shop and he's only open like three days a week. He's been around since the early 70s. He said this was the first time he'd ever heard of JIS headsets having different cup sizes--he thought the crown race was the only difference, and says that he's pretty sure that he's unknowingly pressed 30.2 cups into 30.0 headtubes.

The difference between him and the other shops I talked to, though, was that he actually went back to his tange catalog to check, and thus discovered that 30.0mm cups actually do exist. The other ones I talked to just said that there is no such thing, that JIS only refers to the crown race diameter, or that 30.0mm cups are a real thing, but nobody makes 30.0mm cups anymore.

Just out of curiousity, does anyone know what the difference in quality is between the tange passage that I ordered and the slightly more expensive tange levin cds that I originally had planned to use before I realized it was the wrong stack height? Are they machined to the same standards? Is the levin just more popular and therefore more expensive? I notice the passage is slightly lighter, so maybe the $5-10 difference just reflects slightly more robust parts in the levin I guess that would be consistent with the passage having a lower stack height). Anyone know the answer?