I have a 1986 Azuki Imperial with a rather short stem (50mm). I bought it off of craigslist a year ago, and all of the components apear to be orginal. I am very happy with the bike overall, but want to replace the stem with something a bit longer, around 80mm.

Am I safe in assuming that a stem advertised as fitting a 1" stem and accommodating a 25.4mm handle bar would be the right choice? I have tried measuring, but without a caliper (and with not so good eyesight) it is a bit of a guessing game.

Assuming it's a quill stem, although all 1" steerer tubes all have a 25.4mm O.D., the wall thickness varies so that the I.D. of the steerer tube also varies. Most quill stems have a 22.2mm diameter, but some older road bikes and even more recent MTBs have thicker walled steerers and take 21.1mm diameter quill stems.

So no, it's not a slam dunk that any 1" quill stem will fit your bike. Your best bet is to either look for the diameter stamped in your stem, or use a caliper to measure it.

Thanks for the response. I'll see if I can round up a caliper, and take a closer look at the stem.

In terms of replacing the stem, how difficult is it? I've looked through several books, and it looks fairly straight forward. I am fairly new to bicycle maintenance, but am generally handy.

Once you determine the correct diameter, there will be only two potential significant issues in changing stems.

The first is the dreaded "stuck" stem where electrolysis has occurred between the stem shaft/quill and the inside wall of the steerer tube. For tips on fixing this, check out Jobst Brandt's article on stuck stems, or google "stuck handlebar stem."

The second issue is less obvious, but potentially dangerous. Don't raise the stem above the minimum insertion line engraved on the stem. If the line is visible above the headset lock nut, it's too high and could accidentally come out while riding. If the stem doesn't have a minimum insertion line, a good rule of thumb is to have at least 2" of the stem in the fork steerer tube.

Just as having the stem too high, it can also be too low. Most steerer tubes are internally butted at the bottom where the tube is brazed to the fork crown, and if the quill is too low in the steerer it can be in the transition area between the non-butted and butted sections of the tube. You may think it's secure, but when riding the stem quill can lose its grip on the wall of the steerer, come loose, and ruin your day.

Both of these potentially dangerous conditions are explained in Sheldon Brown's article on adjusting handlebar height (scroll to the bottom of the page for a good illustration by Nicholas Flower of the problem encountered when the quill is in the transition part of the steerer tube).

One other tip: before installing the stem (or a seatpost for that matter), apply a thin coat of waterproof grease to the surface of the stem shaft that will be in contact with the fork steerer tube. This will mitigate the corrosion problem, making it much easier to remove later.

I'm presuming the 25.4mm is the clamp diameter.. if you have a drop handlebars, they could potentially be either 25.4mm or 26.0. if your handelbars are 26.0 at the clamp then that stem won't work for youo

Excellent point.

You could use a shim to fit 25.4mm clamp diameter bars into a 26mm stem clamp, but not the other way around.

i have filed a 25.4mm stem to be 26.0 but i wouldn't recommend doing that to a new one

I've managed to do it, but it was a struggle.

I agree that it's possible to do, but it could put excessive stresses on the clamp and lead to premature failure.

Just a quick update to close out the thread.

I ended up using a very low-tech approach to measuring both the stem and the handebar diameter. I used a drawing program (Visio) to draw out circles of various circumferences, and printed out the page. I very carefully cut out the circles, and used the remaining template to determine the sizes for the stem and handlebar.

I just received the new stem, and will be installing it shortly.

Therer is a simpler way. Cut a strip of paper, about 5mm wide by 100mm long. Tightly wrap it around the stem or bar and mark where it overlaps with a sharp pencil. Unwrap and measure the distance from the end to the mark. Divide the measurement by 3.14 to determine the diameter. Repeat, to ensure accuracy. Using this method, I consistently obtain results with 0.2mm of those provided by calipers.

https://www.harborfreight.com/6-inch-...iper-7914.html

No bike mechanic should be without one.......

Impress the ladies and be one of the kool kids.

^ got a recommendation for a cheap digital one?

^ I bought one of these and have no complaints:
https://www.ebay.com/itm/6-Digital-LC...item3a5b8520ec

SOLD! thanks i've been needing to get one

Further update:

Long story short, the stem was the diameter (both for the steering tube and the handlebar), but was a bit too long. The bike is a small frame (20") and the stem would have been too high. Argh!

After some research on the forums, I decided to try and cut it down (a little less than an inch). The andgle was a bit tricky, but I managed to cut it properly with just a hacksaw and a vise. Cleaned it up with a file, and it appears good to go.

This whole wrenching thing may start to become addictive.

I like happy endings.