There is no provision for adjusting belt tension in any Beogram.
A too loose belt will have to be replaced and a too tight belt will put a too high
pull on the motor holding bracket and it's rubber grommets, sometimes
even destroying the grommets.
A new (correct) belt will easily stretch the small amount needed to just slip on without
losening the motor bracket etc.
I can supply correct belts for Beogram 4000, 4002, 4004 and 6000 and
hopefully soon also for the Beogram 1800 in that I am currently testing
a new prototype. Actually, I could use a second opinion or two on these - PM me !
Martin