The weakest links on the XT350 engine,
1. Timing chains are not long life items. They stretch bad. I had to replace mine at about 10k miles.
2. Timing chain tensioner.
3. Intake boots.
I've you an complete YZ490 chassis beside the shop,
I'm actually thinking about putting my XT350 engine in it,
Would solve all the weak links of the XT350 chassis.