I can't quite picture how the chain fouls the frame on the lowest gears, especially as a result of a large chainwheel. I'm not familiar with the bike though.David Collier wrote: Thanks Duck for info on freewheel thread size. I see a freewheel on epay with one less tooth on top gear and fewer teeth overall which is all I need. Have a large chainwheel which means the chain presently fouls the frame on lowest gears. Without the motor it had a 7-speed freewheel; with it only room for a 6 speed. This is a well made all-alloy bike: didn't know KIA made such bikes before noticing it at local recycling centre.
Normally a 6-speed freewheel has cogs that are spaced a bit further apart than 7 speed freewheels, which means that the whole freewheel is not a lot narrower than the 7 speed and the different spacing means that the shifters won't move the chain far enough to engage the next cog properly. As a result if you have to change from 7 to 6 speed you will usually (see below) need to change shifters as well.
There is a possible alternative solution to changing shifters with some old parts from the 80's which still turn up occasionally. Sun-Tour made 6 speed freewheels with their Ultra-6 spacing, which is close enough to 7 speed to work with 7 speed shifters and derailleurs. (They also made 6 speed freewheels with their regular 6 speed spacing). I had a bike working nicely with an Ultra-6 Perfect freewheel and Microshift 8 speed shifters (7 and 8 speed shifters are the only ones that play nicely together). I think Suntour Winner Pro were all in the Ultra spacing, but Winner and Perfect models may be either.
6 speed shifters are probably cheaper than an Ultra-6 freewheel of unknown usage.
Cheers,
Cameron