Originally Posted by
HillRider
Unless your current 6-speed is a Sun Tour Ultra-6 on a 120 mm hub, you won't have to change anything but the freewheel. As mentioned above both standard 6 and 7-speed freewheels use 126 mm spacing.
You will have to change your chain unless yours is already a 6/7/8-speed width. You should probably install a new chain anyway to avoid skipping problems with the new freewheel.
I just did install a new Shimano 6 speed freewheel and chain 2 months ago so hopefully the chain should be ok. I think the chain was a KMC Z50. I'm thinking of changing to 7 speed so I can switch out the friction thumb shifter to an indexed 7 speed shifter setup. Maybe also go with the Megarange Shimano 7 speed freewheel. The RD is a Shimano Deore with long cage so I think it should all work together.