Veggie wrote:
dvt wrote:
Veggie wrote:

Can I drop a modern wheel into the bike and expect it to work? Will
there be a gear tooth spacing that can cause problems?

How many cogs are on the old freewheel? Older MTBs had narrower back
hubs and the frame was spaced to match. Your frame might have to
stretch a bit to accept a new wheel. If the frame is steel, the
stretching is no problem. See
http://sheldonbrown.com/gloss_sp-ss.html#spacing for details on rear
hub width and http://sheldonbrown.com/gloss_cn-z.html#coldset for a
few more words about spreading your frame.

The old freewheel has six cogs in it. I'll try to put in a 7 cog
cassette to minimize the stretching, or maybe get a 9 cog and remove a
cog or two.

6-speed hubs are spaced 126 mm, 7-speed MTB hubs are spaced 130 mm. You
should be able to stuff a 7-speed wheel in there if the frame is steel.
It might be a pain to take the wheel in and out when you have a flat,
but it will work just fine once you get the wheel in.

You can't just take a couple of cogs off a 9-speed wheel and make it
fit. The hub will remain the same width (135 mm, too wide to stuff into
your frame comfortably). That's true of cassette and freewheel hubs;
your 6-speed is likely a freewheel hub, while a new 7-speed will
probably be a cassette hub (a.k.a. freehub).

My advice: find a decent bike shop and I'm sure they'll be able to round
up an inexpensive 6-speed wheel for you. Then you won't have to worry
about any of this.

--
Dave
dvt at psu dot edu