bikemig 

I am rebuilding a 1992 Specialized stumpjumper that needs a new headset. I happen to have a NOS suntour XC pro italian threaded headset sitting in my parts bin looking for a home.

I know people install english threaded headsets all the time on italian bikes but there are differences right which means that once you install an english threaded headset on an italian threaded fork, you should stick with english threaded headsets, right?. I know this is true if you install an english threaded freewheel on an italian threaded hub.

I was looking at my trusty Sutherlands (20th anniversary) and the differences between ISO and Italian look pretty small. The threads on both are 25.4 x 24 TPI. The Italian cups run around .2 mm larger than ISO. The crown race is marked 26.4 on my Italian threaded xc pro headset.

I think one difference that matters is that the thread angles are a bit different which means you just don't want to go back and forth too often between english and italian headsets.

The alternative would be to simply use the bottom half of the Italian threaded XC pro headset and keep the top part of specialized branded headset currently on the bike. I opened up the existing headset and it's the bottom (no surprise) which needs replacing. That would be a frankenstein headset but what the heck, both are black. That would not look bad and it would be easy. This is one time where mixing parts might be the right answer.

Sutherlands has the "italian" bottom headset cup as .2 mm larger in outside diamater than ISO HS cup (30.2 mm versus 30.0 mm). Is that going to be a problem?

P!N20

Yes, that's the popular opinion.

I wouldn't have thought that would be a problem unless you were mixing and matching your races.

randyjawa 

When the original owner of an old Torpado that I bought, installed a 27 fork, replacing the damaged 700c on, he installed a complete Italian head set. Everything seemed tikkety-boo until I found this...


So, be forewarned, the lower English cone is too small for the fork fit. My opinion, but my opinion coincides with Sheldon's. Anyway, I installed a 700c fork and used everything that came with the Torpado except the bottom cone. Seems OK so far but I have not really gone far, on the bike, since the fork was installed. I did take the bike out for a short spin and all seemed good except for one thing...

Forgot to snug up the seat post bolt. By the time I was a quarter mile away, the saddle was all the way down to the seat lug. I walked the bike home.

bikemig 

Good point about the way things can go wrong if you force fit a piece. That's the fork crown race, right? I think I'll be fine with that since the crown race on my italian threaded suntour headset is marked at 26.4.

bikemig 

I think the real potential problem with using the bottom half of an italian threaded headset on my 1992 Stumpjumper is likely the outside diameter of the cups which are 30.0 mm for ISO and 30.2 for Italian. The stack height will not be an issue.

When installing an english threaded headset on an italian threaded fork, that's not a problem since the cups will be .2 smaller than the dimensions on the headtube.

But when installing an italian headset on an english threaded fork and a headtube with ISO dimensions, the cups will be .2 mm too large. Now that's the same difference in trying to install a 22.2 quill stem (ISO) on a French bike that takes a 22.0 quill stem. Not a big deal to sand .2 mm off a stem to make it fit but I don't plan on doing that with the headset cups given how thin they are. I could try to take some material of the headtube but that's a lot harder material and I don't have the tools for that. Or I might just get lucky given manufacturing tolerances. Sometimes a 22.2 stem just drops into a french bike and maybe this slightly oversized cup will do the same.

I was hoping someone had tried this out but maybe not. Well I'll have to report back to the team if this works.