Engine: Top End Construction

Valve Covers

- contains oil being splashed around valve galley- allows easy access for inspection and top end adjustment or repair

- usually holds positive crankcase ventilation valve (PCV valve)- cap for adding engine oil is usually found on this part

Valves

- allows air fuel mixture or exhaust gases to enter and leave the engine- intake valves are always bigger in diameter

- are restrained in size so multiple valves are used in a single cylinder- exhaust valves are sodium filled to absorb more heat

Valve 101

- Margin is the useable amount left to re grind if needed- The seat seals against the face of the valve

- The valve guide keeps the stem of the valve centered

Valve Issues

- valves need to make a good seal in order to contain high pressures- loss of pressure is due to burnt valve, carbon deposit build up, bent

valve, or loose valves (worn valve guides)

Valve Performance

- stock sealing surface is 3 angles to allow for better air flow/sealing- performance valve grinds will do 5 angles which include back cutting

valve for even more Cubic Feet Per Minute

Valve Performance

- stock valve is in the center-Vortec valve is on the left and incorporates a 30 degree back cut

-Manley stainless valve is on the right and uses a thinned valve stem for improved air flow and lightening

Valve Contact

- Prussian Blue (engineer’s blue) is a dark dye mixed with oil - The prussian blue is applied to valve only and valve is rotated against

seat to see where the valve is contacting

Valve Contact...

- lapping compound is oil mixed with extremely fine grinding grit-Lapping sticks are used to suction to the face of the valve

-Valves are rotated with lapping compound to match contact areas- once completed, Prussian blue is used to recheck the lap

Valve Keepers

- valve keepers prevent the spring from releasing when installed- Keepers also allow the valve train to be disassembled

-- need to have valve spring compressed to remove/install keepers

Valve Keepers...

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Valve Springs

- the spring allows the cam lobe to open the valve (compressing the spring)

- valve springs’ job is to return the valve face against the seat and ensure a good seal as fast as possible

Valve Train Operation at 14,000 RPM

Valve Springs Float

Valve Spring Compressors

Valve Seals (umbrella seals)

- valve seals allow a small amount of oil to lubricate the valve stem without excessive amount passing into combustion area (blue smoke only at start up)

Rocker Arms

- rocker arms redirect forces from pushrods to the valve- Each valve will have one rocker arm to allow for independent

adjustment- most common type is a solid rocker arm

Rocker Arms…

- Rocker arms use set screws and lock nuts to allow for valve lash adjustments (play in between rocker arm/valve)

- Feeler gauges are used to check the play and are accurate to .001”

- Some valve lash is needed to allow for expansion/low friction/ensure that valve is not held down even a little

Rocker Arms…

- Roller rocker arms are used in diesel and performance engines to reduce friction and wear

- roller rocker arms still need valve lash to be adjusted

Pushrods

- Pushrods are light rigid tubes that transmit force from the lifters to the rocker arm

- They are hollow to allow for oil to lubricate contact points

Lifters

- lifters transmit force from camshaft lobe to pushrods- One end slides up and over the lobe shape (high friction)

Hydraulic Lifters

- roller lifters have reduced friction and wear- Hydraulic lifters use oil pressure to remove any play or

looseness in the valve train

Camshaft

- Camshafts control the timing of the intake/exhaust valves opening and closing

- They also control how much the valves open (lift) and the length of time they are open (duration)

Camshaft…

- Camshaft specifications are design to meet certain driving conditions: fuel economy, more torque, more horsepower, low emissions

- Camshafts are heat treated to resist wear and are ground to extremely tight tolerances based off the engine requirements

Valve Overlap

- Valve over lap allows the fresh air fuel mixture to push out all of the exhaust gases

- back pressure also helps to pressurize the combustion area

Variable Valve Timing

Camshaft…

- Camshafts can be single over head cams (SOHC) or dual (DOHC)- They are attached to a sprocket that is driven from the

crankshaft by means of chain/belt/gear

Performance Camshafts

- In order for camshafts to be light and spin faster, manufacturers produce hollow camshafts and hydroformed camshafts

Cylinder Head

- Cylinder heads hold the position of the valve train and house the combustion chamber

- they are made of aluminum or cast iron and contain passages for oil and coolant to flow through and cool/lubricate parts

- They also have passages (ports) to allow the air/fuel mixture and exhaust gases to pass to and from the combustion chamber

Volumetric Efficiency

- Volumetric efficiency is the amount of air brought through the engine compared to the theoretical maximum

- The more air the engine can “breathe” the more power- This is the key to increasing power in an engine

Cylinder Head Porting & Polishing

- Stock cylinder heads are often sand cast and the ports that move air have a rough texture and are poorly sized

Cylinder Head Gaskets

- Cylinder head gaskets must hold in high compression pressures and allow oil and coolant to pass without having leaks

- When changing head gaskets, ALL old material must be removed before a new is installed

Cylinder Head Sludge

- Oil needs to be free to flow up to oil the top end components- It also must be able to drain back through the tiny oil returns

Cylinder Head Gaskets...

- High compression engines require copper gaskets- Copper gaskets can be reused if annealed (25% elasticity)

Exhaust Manifold

- Exhaust gaskets are needed between the head and the exhaust manifold

- Studs are usually threaded into the head instead of bolts- Exhaust manifolds direct hot gasses towards the exhaust system

and are usually made of cast iron to hold up to the intense heat

Intake Manifold

- Intake manifold gaskets provide a seal between the head and the intake manifold

- Intakes are made of aluminum and sometime plastic that has smooth surfaces to help with air flow

- Intakes sometimes have multiple runners to provide different lengths during different running conditions

Intake Manifold

- Intake runners can just move air (direct injection) or they can run air/fuel mixtures such as older V8 engines