Bicycle Mechanics - Freewheel and Chainring Compatibility

My bike currently has a 7-cog Shimano freewheel, exact model unknown, but it is a MegaRange with 34-tooth low gear. Is it possible to upgrade to a different model Shimano 9-cog with a 34-tooth low? I know I would have to change the shifter, also. What information do I need to obtain to determine compatibility? Are there resources that cross-reference compatible/interchangable parts like this? At some point I may wish to upgrade the chain rings to the same Shimano model as the new freewheel. How do I determine whether the new chain rings will fit my bottom bracket? Both of these upgrades seem fairly straightforward and doable by a home mechanic. Am I correct in that assumption?
Thanks,
Raymond

At best you will need to install a new freehub onto the present hubset, to get the 9-speed cogset to mount, but you'll porbably need to buy a new hubset. Shimano is notorious for changing parts just enough to make upgrades impossible without buying a bunch more stuff. You probably need to install new chainrings if you do mount a 9-speed freehub as the spacing between the rings has changed and you will need a narrower chain for the narrower cogs in the rear. The new chainrings should work as long as ALL of the dmensions on the crankarm SPIDER are the same as the 9 speed variety. I believe they are but I could be wrong. Your current 7-speed rear derailleur will need to be replaced as well and the shifters too. Full upgrade kits are available from what I understand, but are advertised as 8spd to 9spd
TALK TO YOUR LOCAL SHOP, AND TAKE YOUR BIKE WITH YOU!

Note: Dura-Ace Parts as a rule will not work with anything else in Shimano's line

[Edited by pat5319 on Dec 28th at 10:50 PM]

You may find your dropout spaceing will not accomidate 9 speed. They can be spread out by a good mechanic, but i would probably just buy a new bike. As it sounds like that`s a pretty old one anyway.!!

Rainman,
You are going to need a new rear hub, a new crank, new shifters, new chain, new front der. new rear der. The der. are providing that you have old school 7 speed stuff like Suntour XC Pro, shimaNO DX and the like. You may even need a new B.B. if you go splined or can find a compatible square hole crank. 8 speed cranks, der., and b.b will work. You will not need to have your rear stay's spread as you can always re dish the wheel. Finally yes check with your local LBS.

Thanks for all the information. I was afraid it would be more involved than it seemed in terms of the number of components that would require replacing. I'll just bank the pennnies and start saving for a new bike. Now ain't that a shame? :-)
Regards,
Raymond

Rainman P,

You do not need all that.

All you eed is a freehub body. Better may be to buy any cheap 8s/9s rear hub. Of course the new 9s cassette that you want and new shifter as it will need 9 click. However if you have older friction, you do not need this. You may also spend $10 on a new chain as you old chain may be really worn out. That is it.

As mentioned by someone. Your frame will be spaced narrower. Simply spread the new hub in. No problem. You are done.