Cylinder Head Components CHAPTER 12 Cylinder Head Components

Introduction The cylinder head is an integral part of the engine. End cap for combustion chamber Admits air and fuel and exhausting gases Prevents engine from overheating

Cylinder Heads (Gasoline Engines) (1 of 14) Intake of air/fuel Compression of air/fuel Ignition of air/fuel Power stroke Exhaust of burned gases

Cylinder Heads (Gasoline Engines) (2 of 14) Cylinder heads can be made of cast iron or aluminum alloy. In most vehicles today, made of aluminum

Cylinder Heads (Gasoline Engines) (3 of 14) In overhead valve (OHV) engine, valves positioned in cylinder head assembly directly over top of piston.

Cylinder Heads (Gasoline Engines) (4 of 14) In OHC engine, camshaft inside cylinder head, directly actuates valves via cam followers or rocker arms. More expensive cam drive and enhanced oiling

Cylinder Heads (Gasoline Engines) (5 of 14) Dual overhead cam (DOHC) engine contains two camshafts per cylinder head. One camshaft operates intake valves; the other operates exhaust valves.

Cylinder Heads (Gasoline Engines) (6 of 14) Cylinder head is composed of many distinct parts. Bare cylinder head casting Intake valves Exhaust valves Valve keepers Valve retainer

Cylinder Heads (Gasoline Engines) (7 of 14) Cylinder head is composed of (cont’d): Valve springs Oil seals Valve stem seals Rocker arms Plugs (galley, coolant) Camshaft

Cylinder Heads (Gasoline Engines) (8 of 14) Combustion chamber inside engine is where fuel and air are compressed by piston then ignited by spark plug. Formed into cylinder head during casting process Efficiency determined by design

Cylinder Heads (Gasoline Engines) (9 of 14) Improve swirl and turbulence of air/fuel mixture Shape and angle of intake port Turbulence increased in quench/squish area Squishing air/fuel into small charge

Cylinder Heads (Gasoline Engines) (10 of 14) Hemispherical cylinder 1901 Intake valve on one side; exhaust valve on other Good cross-flow of gases Spark plug near center of chamber Flame front = flame propagation

Cylinder Heads (Gasoline Engines) (11 of 14) Bathtub combustion chamber oval, shaped like an inverted bathtub Valves mounted vertically side by side

Cylinder Heads (Gasoline Engines) (12 of 14) Wedge combustion chamber tapers away from spark plug. Valves straight line positioned along tapered angle Speeds velocity of flame front

Cylinder Heads (Gasoline Engines) (13 of 14) Gas direct injection (GDI) cylinder head Gas injected directly into combustion chamber Controls fuel Improves fuel economy by 35%

Cylinder Heads (Gasoline Engines) (14 of 14) Size of intake and exhaust ports in cylinder heads affect engine output. Smaller intake and exhaust ports allow engine to develop more torque at low engine speeds. Larger intake and exhaust ports allow greater airflow during engine’s high-speed operation.

Valves and Valve Trains (1 of 22) Valve trains are responsible for moving air and fuel through engine. Experience enormous stress even under normal circumstances

Valves and Valve Trains (2 of 22) Valve tip Keeper groove Valve stem Valve face Valve head Valve margin

Valves and Valve Trains (3 of 22) A four-valve arrangement usually has two intake and two exhaust valves

Valves and Valve Trains (4 of 22) Poppet (mushroom) valve Pops up/down to open and seal Red-hot under high-power conditions Stands up to spring and combustion pressure Hollow stems

Valves and Valve Trains (5 of 22) Intake valves are made of steel mixed with chromium or silicon to make them more resistant to corrosion.

Valves and Valve Trains (6 of 22) Valve guides are hollow metal passageways. Valve moves up and down only. Must retain lubrication Cannot be lubricated with insufficient clearance

Valves and Valve Trains (7 of 22) Integral valve guide (non-replaceable valve guide) Cannot be removed or replaced Repaired by machining it and installing a thin wall bronze liner

Valves and Valve Trains (8 of 22) Non-integral valve guide (replaceable valve guide) Removed and replaced as needed for repairs Cast iron or bronze

Valves and Valve Trains (9 of 22) Valve stem seals used on intake and exhaust valves Control oil that lubricates valve stems Allow just enough oil to lubricate valve stems and guides

Valves and Valve Trains (10 of 22) Cylinder heads have one of three types of valve seals. Umbrella-style O-ring Positive

Valves and Valve Trains (11 of 22) An O-ring valve stern seal. A positive valve stern seal.

Valves and Valve Trains (12 of 22) Valve seat mates with face of valve. Hardened steel Compatible with today’s gasoline Ground or cut Seal tightly Interference angle for quick bedding-in

Valves and Valve Trains (13 of 22) Valve train controls opening and closing. OHV OHC DOHC

Valves and Valve Trains (14 of 22) Camshafts provide motion to open and close. Cam lobes Lift Duration Lobe separation angle

Valves and Valve Trains (15 of 22) Engine lifter in the engine block and cylinder head. Engine lifter in between the cam and the valve tip (bucket style)

Valves and Valve Trains (16 of 22) Most OHC use camshaft. Same function as rocker arm Pivot on one end; slider or roller near center

Valves and Valve Trains (17 of 22) If camshaft is on top of valves, engine will use bucket-style lifters. Hydraulic or mechanical

Valves and Valve Trains (18 of 22) OHV engines incorporate pushrods to transfer motion from valve lifter to rocker arm. Ball to ball Ball to cup Ball to adjustable tip

Valves and Valve Trains (19 of 22) Rocker arm pivots inward. Direction change OHV or OHC Different ratios Different styles Stamped, cast, or forged

Valves and Valve Trains (20 of 22) Valve springs close valves and hold valve firmly against valve seat. Coil spring Must meet specs One spring or multiple springs

Valves and Valve Trains (21 of 22) Valve spring retainers are used along with valve keepers to hold valve spring in place. Steel Valve rotator Exhaust valves

Valves and Valve Trains (22 of 22) Valve keepers (valve locks) lock valve system to retainer. Split taper design Hardened to withstand opening and closing valves

Gaskets (1 of 8) Gaskets form seal by being compressed between stationary parts where liquid or gases could pass. Generally designed to be single use

Gaskets (2 of 8) Made of soft materials. Cork Rubber Paper Brass Copper Aluminum Stainless steel

Gaskets (3 of 8) Gaskets today are made from vulcanized rubber or EPDM. Some gasket materials swell once put into service to increase sealing ability.

Gaskets (4 of 8) Head gaskets seal and contain pressures of combustion within engine, seal oil passages, and control flow of coolant. Anisotropic Provide or adjust proper clearances

Gaskets (5 of 8) Some incorporate stainless steel fire rings. Late-model vehicles have a multilayer steel (MLS) head gasket.

Gaskets (6 of 8) Oil seals seal rotating parts of engine. Valve stem seal uses similar sealing principle. Stationary or sliding shafts can be sealed using O-rings. Seal two surfaces in stationary contact with each other.

Gaskets (7 of 8) RTV silicone is one of most popular types. Only to fill gaps with small amount Oxygen sensor-safe RTV on engines with oxygen sensors

Gaskets (8 of 8) Contact cement is most popular adhesive. Valve cover gaskets Fuel pump gaskets Intake and exhaust manifold gaskets

Cylinder Head Diagnosis Cylinder head problems can affect engine function. Cracking Holes Leaking Warped cylinder head Burnt or warped valves Stripped spark plug hole threads

Cylinder Head Repair (1 of 4) Thermal stress is main cause of cylinder head cracking. Removing cylinder heads should only be done after extensive testing. Always clean cylinder head after removal.

Cylinder Head Repair (2 of 4) Valves and valve seats should always be inspected when cylinder head is removed from engine. Valves and valve guides should be measured. Correct size and strength of valve springs are critical to engine operation.

Cylinder Head Repair (3 of 4) Cylinder head will need to be reassembled after work on valves, springs, and head is complete. Pushrods and rocker arms should be inspected at each point of contact. If camshaft is being reused, measure and inspect cam lobes and journals.

Cylinder Head Repair (4 of 4) Camshaft bearings support camshaft and are critical to operation. When installing camshafts on bucket lifter head, install intake camshaft on the intake valves and exhaust camshaft on exhaust valves. Heads that use cam followers or rocker arms begin with installation of camshaft, or rocker arms might need to be installed first.

Summary (1 of 17) Functions of the cylinder head include: admit air and fuel to combustion chamber, release exhaust after combustion, and allow coolant to flow around the top of the combustion chamber. The cylinder head forms the top of the combustion chamber and is securely fastened with a head gasket.

Summary (2 of 17) Cylinder heads may be aluminum alloy (lighter weight, boosts fuel economy) or cast iron (heavier, but lower engine operating temperatures). Engines may be overhead valve, overhead cam, or dual overhead cam.

Summary (3 of 17) Cylinder head parts include: base cylinder head casting, intake valves, exhaust valves, valve keepers, valve retainers, valve springs, oil seals, coolant seals, rocker arms, plugs, and camshaft. Cylinder heads improve the swirl and turbulence of the air/fuel mixture moving into the combustion chamber. 54

Summary (4 of 17) A hemispherical (HEMI) combustion chamber has intake and exhaust valves located on opposite sides to create cross flow of gases. The amount of air an engine can take in and remove is referred to as “breathing.” The greater the air/fuel mixture, the more heat is generated, and thus more engine power.

Summary (5 of 17) Dual overhead cam engines often have multivalve cylinder heads to create quicker, more efficient air/fuel movement. Cylinder head shapes can be oval (bathtub), wedge, or gas direct injection (GDI).

Summary (6 of 17) Smaller intake and exhaust ports are generally better for vehicles operating in low gear (four-wheel drive), while larger intake and exhaust ports are ideal for engines operating at high speeds. Components of the valve train are driven from the camshaft and include: lifters, pushrods, rocker arms or cam followers, valves, valve springs, keepers, and retainers.

Summary (7 of 17) Components of the valve are: valve tip, keeper grooves, valve stem, valve face, and valve margin. Valves are located in the cylinder head and are configured in two-, three-, four-, and five-valve arrangements. Most vehicles are fitted with poppet (mushroom) valves.

Summary (8 of 17) Exhaust valves are designed to withstand higher temperatures than intake valves. Valve guides are integral (non-replaceable) or non-integral (replaceable) and are designed to limit a valve’s movement to up-and-down and retain lubrication for the valve stem.

Summary (9 of 17) Valve stem seals are designed to prevent oil leakage; the three basic types are umbrella style, O-ring, and positive. Valve seals form a strong seal with the valve face and must withstand high temperatures and extreme pressure. Valve train refers to all the parts that contribute to the opening or closing of the intake and exhaust valves.

Summary (10 of 17) Types of valve trains correspond to engine types: overhead valve, overhead cam, or duel overhead cam. Rocker arms are categorized by the ratio of movement on the valve side to movement on the push rod side.

Summary (11 of 17) Push rods, found in overhead valve engines, transfer the motion from the valve lifter to the rocker arm; push rod types are: ball-to-ball, ball-to-cup, and ball-to-adjustable tip. Lifters can be solid (manually adjusted) or hydraulic (self-adjusting) and are located in the engine block, cylinder head, rocker arms, and between the cam and valve tip.

Summary (12 of 17) Camshaft followers are used in overhead camshaft engines in place of rocker arms. Bucket-style lifts transmit movement from the cam lobe to the tip of the valve. The valve spring is designed to close the valve and exert pressure to hold it firmly against the valve seat.

Summary (13 of 17) Valve-spring retainers and valve locks (keepers) hold the valve spring in place. Gaskets are designed to create a seal when compressed between two stationary parts. Gaskets are single use only and must withstand engine heat. Functions of a head gasket are to seal and contain combustion pressure, seal oil passages, and control coolant flow.

Summary (14 of 17) Anisotropic head gaskets conduct heat laterally. Oil seals can seal the rotating parts of an engine and are made of rubber or a rubber-type compound comprised of silicone, EPDM, or other flexible material. The lip-type dynamic oil seal is the most commonly used type.

Summary (15 of 17) O-rings are used to seal stationary or slowly rotating shafts. Sealants are designed to seal together two surfaces in stationary contact with one another. Always check manufacturer recommendations for the proper type of sealant.

Summary (16 of 17) Common cylinder head problems include: wear, cracks, leaking coolant or compression gases, warped cylinder head, burnt or warped valves, and stripped spark plug hole threads. Thermal stress is the main cause of cylinder head cracks.

Summary (17 of 17) Many cylinder head repairs require the skill of a certified machinist. Only remove the cylinder head after extensive testing and uncertainty that removal is required. Always clean the cylinder head after removal. Test valve springs for squareness and measure both spring height and installed pressure.

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