Bicycle Mechanics - JIS head tube ISO Fork, what are my options?

Hey all,

So, my dream project (my dad's bike) has come with a weird twist. The headset was completely rigged with parts from 2 complete headsets (think 1 jammed in the other). Anyways, I took out all the crap and I realize that the fork is ISO but the head tube is JIS. Has anyone ever successfully mixed an ISO fork with a JIS headtube, and how did you do it and did it last. I'm guessing that there's some fix to this issue, but I can't place my finger on it. I guess I would buy two tange headsets and use the JIS half on top and the ISO half on the bottom, but I hate being this ghetto. Whaddaya think?



I'd like to buy a used JIS fork, but there's another issue that the steerer itself has to accomadate the 4 5/8" head tube length. Any ideas where to buy a JIS fork?

..I realize that the fork is ISO but the head tube is JIS. Has anyone ever successfully mixed an ISO fork with a JIS headtube,

Sure, the other way around too.


..and how did you do it

Reamed the head tube out to ISO standard.


...and did it last.

So far it's lasting fine, then again I haven't used it for extensive loaded touring yet.

You could ream out the head tube and install an ISO headset.

You could probalby also just install an ISO headset w/o reaming. I accidentally did this. I had a spare ISO headset from when I converted my tri-bike to threadless and I started to install it in my old MTB. I got the cups in fine but realized that the MTB was JIS when I went to install the crown race. When I finally got the JIS headset for the MTB, the cups didn't go in any easier and they definitely aren't loose (i.e. the headtube is not ISO).

Will this work?

Tange Levin CDS Threaded Headset, 1'' Semi-JIS, Chrome (http://www.biketoolsetc.com/index.cgi?id=579252914650&d=single&c=Components&sc=Headsets&tc=Threaded&item_id=TA-CDSC/270)

Who knows because the crown race is ISO (26.4) and the lik mention that crown race is JIS (27) The cups will work fine anyways.

You can try it, the crown race might work. The differences are minimal but sometimes when the fork it is too old the crown race gets kind;a lose...

Give it a try :)

Well actually I have the reverse problem. I need the ISO race with the JIS Cups. Freaking cool product though!

The iso headset should work fine. point two of a millimeter is nothing.

The iso headset should work fine. point two of a millimeter is nothing.

For a steel headtube perhaps, different for aluminium. A friend has a bonded aluminium frame with a cracked headtube casting.

Good question. And, I can't help you. But I would like to say that as a cobbler myself, the situation you have makes me like your dad! Thats good shade-treeing!

jim

have a machine shop reduce the size of the fork crown using a lathe

Good detail. Thanks for bringing it up


For a steel headtube perhaps, different for aluminium. A friend has a bonded aluminium frame with a cracked headtube casting.

actually, I pulled out this shimano 205? (ISO quasi sealed bearings) I have lying around and it will definitely push the cups in. We'll see what happens when I get the crown race off. (my frame is old steal the bike is from the 60's old Hawthorne/Fuji)

But...I may simply buy a new fork with the right crown race setting. What's my best option for getting a new/used steal fork? MY 2 LBSs aren't very forthcoming with the used parts both of them have a huge part of their business fixing up neglected bikes and using their used parts.

I'll need to know how to figure out how long the fork will need to be for me to use and I have no Idea how to do that? The head tube is frickin huge 4 5/8 inches tall. And what does a steal fork cost?

Brian

U have to do the math, measure the bottom and the upper part of the headset plus the headtube length, That will give an idea of how big the steering column has to be. Since you are going to get a new fork have you ever considered to go with a 1 inch threadless fork? Asking because if the new fork needs to be cut and re threaded might be expensive, maybe not. The other thing is that u really dont care if the fork trail match the old one, right?

Good luck.

Ok folks, please review the headset specifications page and get your measurements right before jumping the shark on solutions: http://www.parktool.com/repair/readhowto.asp?id=68

First off, an ISO fork-crown race is 26.4mm, and there's absolutely no amount of work or machining you can to to bring it up to 27.0mm JIS, aside from unbrazing all the parts and rebuilding the fork with a JIS fork crown.

Easiest solution is to bring the frame to a shop with the correct tools to mill the head-tubes out to 30.2mm for ISO headset. Very easy, it's done all the time.

This will be less labour-intensive and costly than replacing the fork. Since the labour to correctly replace the fork will require inspecting and facing/milling the head-tube AND fork-crown race anyway. You can pay for 2/3 steps or 3/3 steps with a new fork. Your choice.

^ I recall you posting up a pic of something you had at home that can do the machine work...

First off, an ISO fork-crown race is 26.4mm, and there's absolutely no amount of work or machining you can to to bring it up to 27.0mm JIS, aside from unbrazing all the parts and rebuilding the fork with a JIS fork crown.


I've found my JA Stein Knurling Tool to do the job, if necessary.
http://jastein.com/Tools_for_Frames_Forks.htm

..an ISO fork-crown race is 26.4mm, and there's absolutely no amount of work or machining you can to to bring it up to 27.0mm JIS....

Not machining, but some rather casual shimming will take the fork up to 27.0 quite easily. The steerer tube is usually a tad narrower above the crown race seat anyhow, and wider below. These features makes it easy both to get the fit started and to get the shim to stay put even at significant assembly pressure.