How do you install a hub dynamo? I want to buy a Shimano hub dynamo, but I'm encountering problems getting a bike shop to commit to installing it for me if I buy it. So I have a couple questions that I'm hoping some of you guys might be able to help me out with.


Can a wheel be rebuilt replacing the old regular hub with the dynamo?  Or does this require a new wheel to be built?  (I've heard once that it's difficult to rebuild a wheel with a rim that has already been built before).
If you can rebuild a wheel, and the hub is a bit larger in diameter than the old hub, do the spokes need to be replaced/shortened, or can they be still be used?  Is there some guideline or rule of thumb about the length of a spoke as long as they're all consistent?
Is the installation of a hub dynamo the same as a standard hub?  I know that the hub has a lot of moving parts inside, but it seems no different on the outside, and I wonder if there are special steps or considerations when installing.


I appreciate any info anyone can give me!  I feel like these bicycle shops have simply never had any experience with a hub dynamo and their first reaction is just "no".

Edit: As a side question, does anyone have any experience with wheel building?  Is this a straightforward process?  This is something I wouldn't mind learning how to do.  Is this the kind of task where you can destroy a wheel or two in the learning process, or will I just need spend more time adjusting to get it right as I learn?
Briefly:

1) yes, you can re-use the existing rim.

2) yes, you could shorten the existing spokes, but that would be expensive and foolish.

3) The installation is the same except now you have wires so you need to plug them into the hub too.

The main issue is (2). Spokes are usually only reused when the rim is being replaced with an identical rim (usually a new one for a worn one), and even then most wheelbuilders will prefer new spokes. Spokes bend a little as they're built into the wheel, and getting those bends in exactly the right place when you rebuild the wheel is effectively impossible. So you'll build the wheel, ride it a little, the spokes will bend back and you'll have to re-tension everything. Usually more than once. If you're paying someone to do this it's cheaper to just buy new spokes.

It's possible to shorten spokes, there are spoke cutting tools for this. They're normally used to make really short spokes (for putting a dyno hub into a 16" wheel, for example) but these days it's possible to buy spokes online in almost any size. But you could sit there and shorten all the spokes in your wheel. But again, if you're paying someone else to do this for you it will be more expensive than a new set of spokes. The tool is also much more expensive than a set of spokes.

If your rim is in good condition that's the bit to keep. If it is worthwhile, you may be better off selling the whole wheel and buying a new rim anyway.