"Jim Edgar" wrote:

Looking for a little more reach on the fixed gear, I've dug through
the parts bin and pulled out an old Cinelli steam (1A, I think).

So, when I put it on the Sakae handlebars, it of course slipped.

Drat - must be one of the Cinellis that used a 26.2, while most
used a 25.8 diameter.

From recycling, I pull out a soda can, which supplies shim
stock of an appropriate thickness. Two layers of soda can
thickness seem to do it.

The old Cinelli standard was 26.4mm, which changed to 26.0mm in the late
nineties. All Sakae bars I've seen have been 1" - 25.4mm. That's immaterial
if your shim fits well.

Is this a good idea or a bad idea?

I can definitely get things tight enough so that it doesn't slip,
but I wonder if I've had to put too much pressure onto the
system - I guess it's the way the little rubber washer has
splayed out a bit. Just a little nervous about slipping bars
on a fixed gear.

A well-fitted shim can be reliable. The ideal is obviously to shim the bar
to the diameter of the stem with as few wraps as possible. It sounds as
though your bar is still somewhat undersized - perhaps not enough to be
dangerous, but probably enough to be creak-prone. Drinks can material I've
used has measured about 0.1mm, so your bar may need a couple more layers.
Open up the stem clamp gently and see if it will accommodate more shim
material. A Vernier caliper is a very useful tool for the home mechanic,
and even a cheap one will be adequate for most bike-related measurements.

In the long term, you could look out for a Cinelli bar to match your stem.

James Thomson