That engine is known for problems. The SOHC has been a good engine though. I would look into the chain tensioner as well, sounds like it lets the tension back off a bit much. I would expect the lower sprocket might have a bit of wear to it too.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.