The valvetrain on the N52 introduced in 2006, used 5 mm valve stems on both
the intake and exhaust. To
increase durability, the exhaust valve stems were increased to 6 mm from 6/06
production.
All of the new NG6 engine have adopted the 6 mm valve stem for the exhaust, the
intake stem remains at
NOTE: If a vehicle has been driven with depressurized air springs, the
air springs must
always be replaced.
Lift vehicle.
Air spring is OK:
when the gaiter cannot be pressed in by hand
when no visible damage (e.g. kinks, cracks, porous areas, etc.) is
discernible
when the rolling fold is unif