I do not know of any consistent problems that have arisen with the valvetrain of the M104. It does not have the upper end oil consumption problems that the M103 has. As far as the timing chain goes, it is a short run double row chain with no complex turns, so it is about as durable as they can get. However, all chains can stretch and you can never know if it needs to be replaced until the stretch is measured.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record