Renovating CB Majestic circa 1980

TUNIWES Posts: 5
edited August 2012 in Workshop
I am renovating a Claude Butler Majestic, complete strip down, frame respray and refit all the original, components. The bike hung in a shed for 10 years has superficial rust on the frame nothing serious, the wheels run true and the bolt on components are coming up like new with a little autosol and TLC
The only problem is I couldn't get the front gear change to change properly, the original bottom bracket has been replaced with a sealed unit which I suspect is the wrong width.
Can anybody tell me please what width BB is best suited to this bike?
The crank is a silstar
Thanks in advance