Konstantin_L

Hi there,

I crashed my Peugeot 103 Carbolite recently and bent the fork at the streerer. I managed to pick up a replacement fork with a threaded steerer of the correct length, but unfortunately I have since discovered that not all 1" forks are the same and my new one requires a 27mm crown race, whereas the headset I have fitted uses a 26.4mm crown race.

Is it possible to replace the whole headset with a JIS 27mm one that would be compatible with my fork? If not, would it be possible to bodge a 27mm crown race into my current headset?

The other option is to mill the fork down, but the bike's not worth much and I'd probably be better of throwing it away sadly, and buying a new (old) one.

Many thanks for any input.

Chombi1 

Wouldn't most older Peugeot Carbolite 103 forks have French threaded/sized headsets?

dddd

I've seen professional bike shops mill a fork's 27mm crown seating diameter to 26.4mm using a file with the fork held in a vise. Some experience is a good thing when attempting this.
Old pro shops should have a simple Campagnolo milling tool that does a better job with less skill required.
Don't bother trying to modify the actual crown race though, it's hardened.

Konstantin_L

Yes, which this is the problem - the french crown race doesn't fit my mystery forks.

mprince

The threading of the fork has no bearing on the crown race dimension - regardless of threading, the 2 crown race standards are ISO and JIS - your fork is one, your crown race is the other. I think the question was more around trying to thread on the upper cup/race (french thread) onto a replacement fork which may not be the same threading.

noobinsf 

I think you identified an issue the OP hasn't discovered yet -- that the original upper cup will not thread onto his new fork.

OP, if your new fork is English threaded, then I think you can just get a Tange headset with 27.0 crown race and English threaded top bits.

icemilkcoffee 

Why would you do this when you can just buy a 27.0mm crown race for $2.78?

Konstantin_L

Yes! I have just independently realised that the thread pitch is wrong, so I cannot use the fork regardless of the crown race.

It seems in lieu of a Peugeot fork appearing on eBay, a new frame / whole bike for me

noobinsf 

Wait, no -- it sounds like you've determined that the proportion of the fork is correct for the frame, so I think you just need an English threaded headset with a 27.0 crown race. I think you can just get a cheap Tange Passage and it would get you going.

Link: https://www.benscycle.com/tange-seik...saAs4zEALw_wcB

Konstantin_L

Thanks, that would be wonderful - so I can in theory fit an English 1" JIS headset with a 27mm crown race in my Peugeot's headtube? Do you know if I'd need to replace the stem too?

Many thanks.

dddd

I didn't assume that the crown race would be readily available at any price, since the OP did not specify what brand it was!

Also, I often (as in almost always) am wanting to finish a job without the wait/hassle/cost of searching for and ordering anything. I guess I'm spoiled in this regard since I have a large cache of used parts on hand, and some fabrication tools, so can almost always get going with what I have.

icemilkcoffee 

Yes

Yes. You need a quill stem with 22.2mm diameter (very common) instead of the french 22.0mm (very rare). And your handlebars could also be an odd 25.0mm french size. In which case plan on finding new 25.4mm handlebars to go with your new stem.

Schlafen

You can file the fork crown from 27mm to 26.4mm, only takes a few file strokes.

Should have no problems unless you use a split race, in which case it will move if not perfectly round. Done it countless times myself.

Fork thread type may be an issue though as others have mentioned, French and English steerer threads are not interchangeable.

Not sure how much a steerer replacement costs where you are but it's about £60 in UK, so all costs factored in, it may be the cheapest option

Or just use bottom half of the new headset and top half of your old headset with the correct thread if it's a cheap runaround bike and you're not bothered.

Konstantin_L

Thanks. I've actually just shelled out on new english headset/stem/bars. Decided it was best to probably change the whole lot and save any potential headaches.

oneclick 

I'd advise against this.

Remember, the bearing balls themselves are accurate to a few thousandths of an inch. A crown race of any quality is going to be ground to the same standard. It also is meant to be an interference-fit on a concentric round seat. I doubt the ability of anyone to hand-file such a seat. No doubt the race can be forced onto whatever polygonal shape results, but just as the seat isn't round - and like as not not concentric either - the race won't be either, forced out of shape and location by the irregularities of the seat.

noobinsf 

Aside from a new bike, this is the best long-term solution. It's best not to mess with shims and jury-rigging the small differences in diameter between modern standards and the French items. Good choice.

jdawginsc 

No matter what bike it is, a new headset, bar and stem combo is not a crusher unless you are wanting to turn a profit. Good to see you trying to keep it alive and used!

JohnDThompson 

You have at least a couple options. 1) you can mill the 27.0mm race seat to 26.4mm to fit an ISO spec headset, or 2) you can fit a JIS spec crown race with ISO spec cups. Many Japanese headsets are available in both ISO and JIS spec, and crown races are sometimes available separately. The head tube fittings are the same for ISO and French headsets (30.2mm), but JIS head tube fittings are slightly smaller (30.0mm). If your LBS has the proper tools, getting the crown race milled to ISO spec is probably the simplest option, as you wouldn't have to dig around for a separate crown race. ISO spec also makes a wider variety of headset choices available.

icemilkcoffee 

You don't have to dig around for a separate 27.0 crown race. You just type in 27.0mm crown race in Google and the first thing (among many similar listings) that comes up is this $2.78 crown race:


I don't understand why people are talking about filing down the fork crown when the proper solution is so cheap and so easily available.

mprince

How do you know that works with the OP's headset? A crown race is not universal like a washer...

icemilkcoffee 

Actually for exposed ball bearing type headsets the crown race is fairly universal.
That might be true for the sealed bearing type as well but I don't have first hand experience there.

Schlafen

I see, the old aerospace bearing tolerances argument, ok no problem I'll raise you a split bearing race and 10 milion integrated carbon bearing seats used in all carbon frames and forks.
Your move, or should I say your click.🧐

noobinsf 

Poop, I forgot about that dimension. Since the OP needs a new headset for the English threaded fork anyway, here is what I would recommend based on all of the above:

- Buy the single $2 27.0mm crown race as recommended above
- Plan to return the JIS 27.0mm headset that you just bought, but do not cancel the order yet
- Order an ISO 26.4mm headset from the same seller
- Plan to simply compare the $2 27.0mm crown race to the crown race that arrives with the JIS 27.0mm headset before returning the headset, just to verify that the dimensions are the same

Does that seem like a reasonable plan? You could also just keep the JIS 27.0mm headset to have a spare top nut, spacer, and caged bearings on hand. Either way, it's still far cheaper than a new bike with unknown problems.

jdawginsc 

I think the OP has already bought a new HS, bars and stem...

Konstantin_L

So if I understand, the 27mm JIS headset will not fit my bike, so I can buy a 26.8mm ISO headset of the same brand and then try to use the 27mm crown race with my fork and this ISO headset.

Plus I can buy a cheapo 27mm crown race and potentially use that instead (if it fits), allowing me to return the JIS headset to the shop.

Is that right?

Is there any guarantee that the ISO and JIS headsets will use the same bearing sizes, even if they're the same brand (Tange)?

I appreciate all the help.