Hydraulic Valve Adjustment Tappets Bucket type hydraulic tappets are used for adjusting the valve clearance. The buckets are self-breathing with a carbon nitride finished cam contact surface. Primary drive Primary drive is provided by a single roller chain from the crankshaft to the two rubber coated cam gears. The train is guided by a centrally positioned V-shaped aluminium deflector rail, a straight rail on cylinder bank 5 to 8 and a curved tensioner rail on cylinder bank 1 to Timing chain adjustment is carried outwith a hydraulic tensioner mounted on the uppercase for cylinders 1 to 4 Secondary Drive Secondary drive is from the intake camshaft to the exhaust camshaft by a single roller chain. Chain tension is maintained by a hydraulic, spring assisted tensioner that incorporates an oil spray jet. The oil supply for the chain tensioner also supplies the VCC hydraulic units through a pressure control valve.