Cylinder Head Assembly: Description and Operation

Cylinder Head and Components
The cylinder head has undergone changes to improve performance and fuel efficiency. Additional changes have been made to improve service and operational characteristics.
Revised porting improves performance and economy, and additional holes in the top deck improve oil draining. Revised load transfer paths give the new head greater resistance to distortion. Additional bosses and tappings provide extra fixing points for the new exhaust manifolds. The torque to which the cylinder head bolts are tightened is revised. However, the bolt tightening sequence remains the same.

Reduced Distortion
The basic design of the cylinder head load transfer paths has been revised so that the new head has greater resistance to distortion.

Oil Drain Holes
Additional oil drain holes in the top deck allow faster oil drain-back to the sump.

Intake ports
Revised intake ports help achieve increased performance and fuel efficiency.

Camshaft Bearing Caps




Changes to the bearing cap design, material and manufacturing process enable higher cylinder head clamp loads to be applied.

Cylinder Head Gasket
The cylinder head gasket has been revised to improve sealing. The new gasket has wider reinforcement rings around the cylinder bores and a narrower silicone sealant track The narrower track allows higher clamping loads across the full width of the gasket.

Cylinder Head Bolts
New cylinder head bolts with higher tensile strength are used on the AJ16 engine. The bolt tightening procedure remains unchanged. The tightening torque has been increased and followed by the 90° SPS torque method.

Camshaft
The cam lobe profiles have been altered to provide higher valve lift and longer valve opening as part of the performance and fuel economy improvement program.

Camshaft Cover And Gasket




The new style camshaft cover is made from cast magnesium and accommodates individual "on-plug" ignition coils. The new cover provides superior sound absorption qualities. The cover has a locating groove for the one-piece seal. The seal now includes the two "half-moon" seals that were previously supplied separately.
A cover plate over the on-plug coils improves the appearance of the engine.

Fuel Rail Cover




A silver colored cover is installed over the fuel rail to enhance engine appearance.

Valve Gear
The diameter of the intake and exhaust valve stems has been reduced to 7 mm (previously 8 mm). The lighter valves require less power to operate and produce less noise. The parts associated with the valves have been altered accordingly.