Changing a stem?
 

Background: I have no bicycle maintenance experience except for tightening brakes and installing racks. How hard is it to install a new stem? I have a new stem for my bike, is it pretty simple and easy to do just using youtube/explanations, or should I just take it to the LBS and have them do it? I have allen wrenches etc., I have no idea what is needed or how to do it, although intuitively it seems like just taking the other stem out, taking the handlebars out, attaching them to the new stem, putting the new stem in and tightening it.

What kind of stem ? Most are pretty simple.
Picture ?

This is very simple to do if it's a "regular" road bike stem. The only part that requires some tweaking is getting the handlebars centered again. If you have drop handlebars make sure they are at the right rotation e.g. hoods in the up / down position you prefer. Also make sure that your headset is tight again when your done. I prefer to use a little blue locktite on the portions that cinch the handlebars. It will take you longer to get to the LBS and back then it will take them to do it.

It is in general fairly simple, but there are some safety considerations since it is a control system. Here is an article which you may find useful. Hands Up (Or Down)! Adjusting Handlebar Stem Height on Your Bicycle

Quill or threadless?

I advise against doing this yourself.

It's not that hard, but it's easy to make a stupid little mistake that could cause a bad problem... like losing your teeth.

It would help to know more about the specifics - all stems are not created equal and the technology has changed pretty dramatically in the last 15 years or so with the general replacement of quill stems with threadless. A single picture would help.

A couple things to keep in mind that might help you scope the job:

1. For a threadless stem, the stem relies on friction between the steering tube and the stem for steering control. This makes if very important that the clamping surfaces are clean and free of any lubricant. It also makes the torque of the clamping bolts pretty important. If you don't have a torque wrench or a good feel for this sort of thing, you could overtorque the bolts to where they could suddenly fail or you could undertorque them such that they do not have not have sufficient clamping pressure to maintain steering control in an emergency situation.

2. Also on a threadless system, the preload of the bearings in the steering head depend on the torque of the top bolt that pushes the stem down against the steering head. And this torque needs to be set with the stem clamping bolts loose so the stem can move vertically with respect to the steering head. So the sequence of tightening (top bolt first, then clamping bolts) is critical.

3. If you have a closed clamp where the handlebar attaches to the stem (almost a complete circle around the bar), then you are going to have to completely disassemble everything on at least one side of the handlebar to be able to get the bar and stem separated (e.g., tape, levers, shifters, etc.). This is not difficult, but it is time consuming. If the handlebar clamp has two bolts which removes half the clamp, things are much easier. Same caution about clamping bolt torque here as above.

4. If the new stem has a different stack height from the old (the part of the stem that overlaps the steering tube), you could have insufficient steering tube length to get proper clamping or you could have too much length such that you need to add or shorten any spacers you might have. There are guidelines and tolerances for these dimensions.

This isn't terribly difficult stuff, but it needs to be understood and the consequences of really screwing it up are pretty serious.

- Mark

I had the problem mentioned in #4 of [MENTION=63821]markjenn[/MENTION] 's post. My new stem had a 5mm shorter stack height. Without more/different spacers it would have not been possible to get it right. Another thing is if it's a CF steering tube, over tightening could become deleterious. I'm a little weary of clamping on CF tubes and did buy a torque wrench to use when assembling my CF bike. I picked up a beam type that was recommended by members here for less than $20 shipped. I consider it one of the necessary tools for wrenching on a CF bike.

Or, the OP might have a quill stem.

True, but the three quill stems I have are all closed clamp which requires everything on the handlebar to be removed to be able to "thread" the handlebar into the clamp. So I don't think quill is an assurance that this is a trivial swap.

As all of us have been saying, a picture of the existing stem and the new one would likely resolve the uncertainties about how easy/hard this is.

- Mark

I can't post a photo at this moment, but my current stem IS the kind that involves removing all of the components off of the handlebar, so it will be a bit tough. I'm going to try it with a friend who knows a bit more about bikes than I do and then take it to the LBS if we somehow screw it all up.