Originally Posted by
SJX426
@
verktyg - I do appreciate the your note. I have not seen the 1R break. The 1A break with an under sized bar is not surprising at all. I would also expect the XA to break in a similar way with an undersized bar.
Are the recorded breaks of the XA due to undersized bars?
Both the 1r and XA stems were produced in 26.0mm and 26.4mm diameters. There are no bar diameter markings on the stems. Since many of these stems are old and used, no telling what a previous owner did with them.
The 1r stems were introduced in 1973 so there are some that are almost 50 years old out there!
In 1978 the logo on the plastic plate switched to the "winged C".
Here's a breakdown of the 1r wedge and parts... a picture is worth....
Cinelli Time Line up into the early 80's. No mention of the XA stems. Scroll to the bottom of the page for info on stems.
Velo-Retro: Cinelli Timeline
The XA stems probably broke in the same manner in the 1a stems - primarily from clamping down on an undersized bar.
Opening a bar clamp to fit a larger bar whether it was used with an undersize bar or to fit a 26mm stem to a 26.4mm bar is asking for trouble. If the stem doesn't crack or break during assembly, there's no telling when it could fail catastrophically!
Here's a 26mm 3TTT stem that was probably clamped down on an undersize bar. This is another place where this style of stem can fail.
So... my advice is to thoroughly inspect any older stem and bars before installing them and to periodically check them too. Any bars or stem with any sign of damage should not be used.
Old saying:
"Don't be so cheap, you wont be so rich!" 
verktyg
