Many of you have seen my Quattro Assi build - with Carbon bits hanging all over it:



Well the carbon brakes pads have worn so I thought it time for a tear down and rebuild - and to finally get rid of the last large bit of chrome on the bike - the Shimano 600 Headset.

I ordered a sealed bearing Origin 8 headset in black and ran into trouble when I went to thread it on. The crown race seated perfectly, the cups pressed in perfectly - but the threaded cup and the top nut will not thread on.

Sheldon's headset site says there was an Italian headset with a different pitch - but he said the standard headset would thread on?

Some facts:

• 27.2 seatpost
• Oria RANF tubing
• I suspect the frame to be an 1990/91
• Possibly built in the Tommasini factory
• 26.4 crown race

Here is a shot of the Shimano 600 that threads on with ease:


Here is a shot of the fork threading:


And a shot of the Origin 8 headset:


Anyone have any ideas as to what is going on here? This is a first for me... THANKS!!

The Origin8 is most likely ISO, or very close to "British" threaded. The fork is most likely Italian. Same diameter, same pitch but different thread profile. I forget but one is 60° and the other has a 55° inclusive angle to the thread profile, and one is slightly rounded the other not.

So… Go Italian, or have the steerer chased with a British threaded die.
Just to be sure its not the headset, find a known English threaded steerer and check the fit of the threaded parts.

Italian 2.54x24 and BSC 1"x24 are very similar, with the same pitch and outside diameter. However, it's a case of close but no cigar.

BSC threads typical modern threads with a 60° profile and flat tops and bottoms. Italian threads are Whitworth with a 55° profile and rounded tops and bottoms.

There are also slight difference in the pitch diameter which determines how the parts actually fit together. There are also tolerance issues and your fork may be at the high end of the range and new headset at the low end.

Before doing anything, I'd borrow another BSC headset and see if that fits OK, If so, exchange the new headset. If not, running a die down your fork will shave some material where it counts and allow a BSC headset to fit correctly.

I would encourage you avoid using a regular die tap, these are very sharp and take off more material than necessary. This is a job for a rethreader die and it would be difficult to find for this application. one can be made from a known good part by filing slots in it with a file.

With respect, this is all wet.

There is no such thing as a "rethreader" die. There are dies and chasers.

Dies cut metal, whether they are cutting new thread on a blank. Chasers don't cut metal, but instead force metal to flow back to the desired form. A chaser could be used when a thread is distorted such as in something banged in to it making a flat spot, and it might mash the thread to form if it's close, but cannot be used effectively to shave an oversize (pitch diameter) thread down to size.

Lastly, there's no danger of a die cutting too much metal away (if used properly) since the die has a thread form and only cuts what extends beyond that.

If the die is split, it has a degree of micro-adjustability for pitch diameter. The OP can use the setting screw to open it so it's a tight running fit to the fork, then back off the screw so it makes a skim cut, and thereby proceed by degrees until his headset just fits nicely with a close tolerance fit.

BTW- be sure to use a quality sulfur based cutting oil to ensure good cutting and final finish.

I guess I am confused then - because Sheldon Brown's site says ISO headsets work on Italian threaded forks.. I just googled it again and Velo-Orange even says the same thing:

"Italian headsets are virtually the same as ISO. The crown race ID is 26.5mm rather than 26.4mm and the threads are a tiny bit different, but ISO headsets are so close that they work absolutely perfectly on Italian frames."

AND - how do I find an "Italian" headset - especially in black! LOL

Thanks everyone!

As I said, it's a case of close but no cigar. I'm not sure that you need to shave he fork, which is why I suggested doing nothing until you try another headset.

If, and only if, another headset is also tight would I suspect the fork and shave it. It's equally likely that the headset is undersize or at the very lowest end of the tolerance range, and the correct remedy would be to ask for an exchange.

This is one of those cases of whether to raise the bridge or lower the water. Either would work, but one is more right than the other.

BTW- looking closely at the photos is appears that the headset was a very close no fit, since it appears to go most of the way before jamming. If so, you might be able to wear the thread in by repeatedly threading and removing it, trying to go a bit farther with each pass until it fits and threads freely. If you try this, use some decent oil on the threads, and flush everything clean every few passes. You'll need to use a bit of force to advance at the limits, but don't go so hard that it jams and you can't back it back off.

I have a brand new ISO Ritchey headset and it is the same resistance... so I am guessing your assessment is correct..

Thank you!!

Yeah, ISO and Italian are close but no cigar. It's been a long time since I was a paid wrench, but I don't recall that they were ever easily swappable. It was more like sometimes. It would have generally been considered bad form to use the wrong headset, and it would not have been done on a good bike unless there were pretty compelling reasons.

While the late Sheldon Brown deserves his sainthood for compiling all the information that he did, AFAIK he was never actually a professional mechanic, so it is worth noting that some of his advice should be taken with at least a very small grain of salt.

Also with respect, call it what you will but Snap-on and Mac call them rethreaders. I have 40 plus years of experience as a certified mechanic and have saved and changed many threads with these and homemade ones,fixed many threads that were mangled by a regular tap. In a case like this it can be ideal to push the threads around as needed. Guess I have been all wet for a long time despite my success with my methods. And like you said, if is used properly which is always the challenge especially if you are not experienced and have the right tool for the job.

I should have been clearer. My objection wasn't to the terminology, but to the notion that a die might magically cut away too much metal.

Nothing magical about it, seen a lot of metal removed by inexperience in such cases, no such thing as magic, just skill or lack thereof.

Source: Sutherland's 4th Edition

Right. An English/ISO headset on an Italian thread steer tube is a "class-B" fit; it will work, but avoid going back and forth between fully compatible ("class-A") and "class-B" headsets. If the headset you choose has aluminum threaded parts, no worries. The steel steer tube will re-form the aluminum threads into proper 55° Italian threads.

Take the new headset and thread it on as far as it will go without using great force. Now, support the steering stem as close to the threaded nut as you can and give the nut several taps, all the way around, with a hammer, ensuring to not damage the appearance of the head nut.

Now, after tapping the nut a few times, attempt to thread it on again. Likely, it will thread easier and go on a bit further. If so, repeat the procedure until the nut fits with little or no binding.

This is an old millwright's trick to get a nut to fit without going all the way to the stores counter to get a proper die or chaser or whatever.

Give it a try, you have nothing to loose.