Badgerfun

Please advise! My 1982 XJ650 have been reassembled, but when I try to start, the starter-motor turns on, but there is a rattling noise coming from inside the engine. The rattling noise continues, but the engine does not start, sound as if the starter motor is running around "free", spinning the chain around, not catching the engine. Out of 20 trials 1 might accidentally start the engine... Friend says that the hy-vo chain that is connected to the starter engine is stretched and need to be replaced... Is that possible? Could it be the starter clutch? What to do? If the chain is faulty, where can I get one (at a reasonable price ofc.)? Thanks!