Bicycle Mechanics - Regarding rebuilding a rear wheel

Would it be possible to remove the hub/cog clusters and junk from some random MTB rear rim, and install a single speed coaster hub on it? Im just not sure if the diameter on hubs are all the same where the holes for the spokes are; so im not sure if the spokes would wind up being too long/too short to fit.

I plan to buy/find some cheap old MTB for their wheels/rims this coming spring; I have some single speed cruisers I'd like to get wider wheels on.

It's easy if you get a shop to do it, it should be $20 tops.

Why would I waste $20 on something I can do myself?

Sounds like you are talking about swapping hubs. You likely will need different size spokes. The only thing more invovled in bicycle mechanics than lacing up a wheel is frame building. There are charts/equations for calculating spoke length, based on wheel size, hub diameter, flange diameter, number of holes, lacing patern (3 cross for example)

You may not need different spokes if the flange spacing and spoke circle diameter in the flanges are close to the original dimensions. Take a caliper with you and check it out.

You would need different spokes if you go from geared to SS due to the fact geared wheels are dished and single speed are not.

Wheelbuilding isn't that hard. The tricky part is getting the tension and roundness right. My first and last wheel took me about two hours. Wheel building is also easier if you don't need to dish the wheel, which you wouldn't with a single speed.

If you don't need a fixed gear, you can make a singlespeed by just putting spacers in place of the gears on a cassette hub. It doesn't look as cool, but you still get the one singlespeed advantage, which is a perfectly straight chainline.

I plan to buy/find some cheap old MTB for their wheels/rims this coming spring; I have some single speed cruisers I'd like to get wider wheels on.

What do you mean by wider wheels? The rims and tires on single speed cruisers are as wide as the rims and tires on MTBs.

Maybe american ones yes, but being in Canada not always the case. One of them currently has 26 X 1 3/8 wheels on it which are typically found on 3speeds.. these tires are so uncomfy I find, not to mention much more prone to pinch flats.

The usual 26 X 1 1/2 I can deal with if I feel like buying 26 X 1 3/4 tire treads for them though..