There is an increasing number of reports of lower timing chain failures in Australian released Nissan YD25DDTi engines. The primary (lower) timing chains and gears are a simplex (single row) design while the secondary (upper) timing chains and gears are a duplex (double row) design.
The simplex chains are stretching and ultimately falling, leading to major engine component failure, including valve and piston crown contact to damage. It is advisable to replace the simplex timing chains and tensioners before 80,000kms.
Typically, the timing chain guides and the vacuum pump timing chain sprocket and shaft are found to be heavily damaged and/or worn as well