When I stripped down the old steel Magistroni Senior headset on my Italian frame (dated 1958 - 1961) there was a 180 degree steel shim between the race and the headtube.

Dimensions are:

Fork Steerer OD 25.4 (1")
Magistroni Race OD 30.1
Headtube ID 30.2 - 30.4 (two measurements at 90 degrees)
Shim Thickness 0.37


I can see why the shim is needed.

But I am wondering what this says about the history of the bike.

Would this have been standard practice/ tolerences used by old builders. Was it usual to reem the headtube this much ? Was it usual to use a shim like this. Or is it just sloppy work ?

Is this a sign that the headset is not the original headset ?

Would be interested to hear if anyone has experience of this and opinions, thanks.

The shim was a makeshift repair, but we can't know the cause.

Possibly the head tube was reamed to accept a larger diameter headset (though I never heard of any in this size), and so needed to be shimmed to accept a 30.2 (nominal) headset. This is the most likely scenario if both top and bottom were the same size. (note: your Magistroni cups are smaller than current standard)

It's also possible that a prior mechanic used an adjustable reamer and simply screwed up.

If only the bottom cup is shimmed, the head tube could have become bellmouthed over time and this was a correction.

Shimming headsets isn't a standard practice, but isn't that rare either. Often it's a choice between using a shim or junking the frame, so don't read more into it than there is.

You have a few choices going froward depending on your skill and access to tools. You can simply continue as is, or build up the ID of the head tube with silver solder, or jB Weld, then ream it to the correct size, 30.15 for an ISO headset. You might also try your luck with a JIS (30.2 nominal) headset which might work as is or be close enough for a bearing retainer grade of Loctite to do the job.

Thanks for the insight and advice, much appreciated. The bottom headtube ID is slightly smaller, but both top and bottom had shims installed.

I think it will be best to keep it simple and try and stay with the Magistroni. If I change the headset then the length of the steerer tube may become a problem as well. The Magistroni stack is quite low.