Originally Posted by
Jeff Neese
He said it's currently a 5-speed Suntour. He may be able to get a 6-speed to work, but a 7 or 8 speed probably aren't going to fit unless he's prepared to recenter the axle and redish the wheel. I've had success going from 5 to 6 speed on my Fuji, but that was only because there was enough room to accommodate the small cog being closer to the chainstay.
MB-2’s originally came out in 1985. It originally came with a Shimano 6 speed freewheel, not a 5 speed that is on the OP’s bike. I’ve read the OLD was 130mm.
Going from 6 speed std spacing to 7 speed should not be an issue. Done it a number of times in the past.
John