Mr. Spadoni 

My Stronglight X14 headset that was installed when it came from the builder has been giving me some problems. So I pulled it apart today. Issue is that the bottom cup somehow got dented. Dang, only 20 years use from it. As part of the replacement process, I pulled off the race, and measured the fork crown to see what would fit when I replace this headset. Crown was not particularly cleanly faced and …..it does not measure 26.4. Some places 23.8, sometimes less than that.
Question is…how exact does this need to be? Can I throw something in and expect that the load will keep it in place? Do I need some loctite? A shim?
suggestions?

juvela

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the convention/rule of thumb is that the seat should be .1mm larger in diameter than the I.D of the race

you mention Stronglight

on the V4 model for example the crown race has a stepped inner face so that the seat must be a low one


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Mr. Spadoni 

Here’s the headset in question. Can’t seem to locate the model. And I mistyped the crown diameter . It’s 26.3, not 23.8

juvela

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thank you

this figure makes more sense

there are two main standards for fork crown race i.d. and fork crown race seat diameter

they are 26.5mm and 27.0mm for fork crown race i.d.

"in general" quality sets employ the 26.5 and "ordinary" sets employ the 27.0

suggest first step should be to get the fork crown milled to eliminate this variable as a possible source of difficulty

it is OK to shim when needed; care must be taken not to permit the shim stock to get under the race in the seating process

another technique employed where the distance is very small is to use a centre punch and mallet to make indentations evenly spaced around the vertical surface of the seat

each indentation creates a tiny parapet which very slightly increases the effective diameter of the seat

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JohnDThompson 

Looks like a Stronglight X12 unit.

Crown race diameter of 26.3mm isn't that far off ISO 26.4mm, and should provide a decent interference fit. I assume that the race was properly seated and functioning before you removed it. What does the race seat on the fork measure?

Mr. Spadoni 

Thanks for the ID.
Properly seated? Well, the only other time I had this HS apart, the crown race slid off the steerer when I tripped the fork to take off the bearings. That didn’t seem right, but the HS worked okay afterwards, until it started to bind. On their disassembly, I noticed a dent in the cup, which you can see in the first photo at about 5.30. How that got there is unknown but I am good at breaking things.
The fork measures between 26.4 and 26.28, depending on where I measure. As you can see from the second photo, it’s not the cleanest finish I’ve encountered.

repechage

The lower cup ding can be filed back or nudged out.
the crown race seat...
already borderline too small
I would suggest hand knurling it- stein makes such a tool
or taking a cold chisel and tapping in a series of doinks aligned with the steerer axis.
16-24 equally spaced. Should grow the OD enough to set the crown race.