well timing chain works for long. just like what raccon said in his post. provided the riding is sober. IF the riding is bad then it can go in 3 year. this is what happend to my HHCD100SS/93 model. So I changed it once but later my bike is still with same timing chain. So UR issue is bit annoying me. Well i feel either 1. the riding is bad
2. Oil quality is poor.
3. mechanic don't know how to install it.
4 bad quality bearing which is for cam shaft.
5.worn out timing wheel on crank.
6. misaligned cam shaft or crank shaft timing wheel.
7. timing pad is not proper so it might give proper tension on chain which may cause rubbing the chain on block or related metal spare. Can u please take some of the pisc of u r old chains (close range pics)