My mates just bought an RST and its broke, no suprises here

Anyway, Its a pretty standard CVH, the tapping sounds to be coming from top end of piston no. 1. Is there a known fault for this? Sure there is? If so what's the fix? Have they got lash adjusters/tappits? that can be cleaned or replaced.

Its got an uprated cam and vernier, the pulley hasn't moved and the problems just started. So its nothin to do with clearance etc.