Bicycle Mechanics - Crankset & Front Derailleur Compatibility

I've been mulling over the idea of upgrading from 7-sp to 9-sp. I already have an xt derailleur in the rear, so my thoughts are that I would simply need shifters/cable. I already have a cassette and a chain. Then I got to thinking about the crankset. The current crankset says for IG chains only. I believe it is designed to be compatible with 7-sp...so will the 9-sp chain be too narrow? Along the smae lines, will my nexus FD work with the narrower chain?

If I have to buy a new BB, Crankset, FD and shifters it is quite frankly not worth it to me.

Thanks.

The likely result is that it will work with the crankset you have, depending
in part on how much mileage is already on the cranks. The teeth will be
a bit narrower after 3-6kmi such that the narrower chain is less likely to
be a problem than with a new 7spd CW. OTOH too much wear will cause
the chain to skip as most wear occurs between the teeth on the leading
edge. One speed differentials work best (7<->8) (8<->9) etc. The FD
should work ok as well, a little sloppier than before but should handle the
shifting.

You haven't said what you've got. If the shifters are indexed they'll need to be 9-speed Shimano.

I was planning on replacing the shifters. I've got 7-sp XT index/friction shifters. I already knew they wouldn't work. The concern was with the FD and the crankset. I think the answer from sch is that I probably "should" change the crankset, which to me means I would, which also means this is no longer the quick and dirty upgrade that I wanted.

Thanks for the info!

Is your current Free Hub body long enough for a 9 speed? 8 speed and above use a longer body than 7 speed, although you can use a 7 speed cassette on those with a spacer.