Halderman ch031 lecture

Objectives The student should be able to: Prepare for ASE Engine Repair (A1) certification test content area “B” (Cylinder Head and Valve Train Diagnosis and Repair). Discuss various engine valve types and materials. Describe how to test valve springs. Explain the purpose, function, and operation of valve rotators.

Objectives The student should be able to: List the steps necessary to reface a valve. Describe how to reface or replace valve seats. Discuss how to measure and correct installed height and valve stem height.

Intake and Exhaust Valves Terminology Poppet valve: poppet refers to the shape of the valve and its operation in engines

Intake and Exhaust Valves Terminology Valve guide: holds the valve in place and positions it in the head Portion of the valve that seals against the valve seat in the cylinder head is called the valve face

Figure 31-1 Identification of the parts of a valve.

Intake and Exhaust Valves Parts Involved Valve springs hold valves against the seat Valve keepers (also called locks) secure the spring retainer to the stem of the valve

Intake and Exhaust Valves Valve Size Relationships Engines with cylinder bores from 3 to 8 in. (80 to 200 mm) have intake valve head diameters approximately 45% of the bore size

Intake and Exhaust Valves Valve Size Relationships Exhaust valve head diameter is approximately 38% of the bore size Exhaust valve heads are approximately 85% of the size of intake valve heads

Figure 31-2 Typical valve spring and related components. Dual valve springs are used to reduce valve train vibrations and a spring seat is used to protect aluminum heads.

Figure 31-3 The intake valve is larger than the exhaust valve because the intake charge is being drawn into the combustion chamber at a low speed due to differences in pressure between atmospheric pressure and the pressure (vacuum) inside the cylinder. The exhaust is actually pushed out by the piston and, therefore, the size of the valve does not need to be as large, leaving more room in the cylinder head for the larger intake valve.

Intake and Exhaust Valves Valve Materials Alloy steel Stellite ® Inconal ®

Intake and Exhaust Valves Valve Materials Titanium Stainless steel Aluminized

Intake and Exhaust Valves Two-Material Valves Used when a one-piece design cannot meet hardness and corrosion resistance specifications Inertia friction welding is used to weld valves together

Intake and Exhaust Valves Two-Material Valves Valve heads are made from special alloys that can operate at high temperatures, have physical strength, resist lead oxide corrosion, and have indentation resistance

Figure 31-4 Inertia welded valve stem and head before machining.

Intake and Exhaust Valves Sodium-Filled Valves Used in heavy-duty applications Sodium in valves becomes a liquid at operating temperatures

Intake and Exhaust Valves Sodium-Filled Valves Sodium transfers heat from the valve head to the valve stem

Figure 31-5 A sodium-filled valve uses a hollow stem, which is partially filled with metallic sodium (a liquid when hot) to conduct heat away from the head of the valve.

Valve Seats Integral Seats Formed as part of the cast-iron head of automotive engines

Valve Seats Insert Seats Fits into a machined recess in the steel or aluminum cylinder head Used in all aluminum head engines and applications where corrosion and wear resistance are critical

Figure 31-6 Integral valve seats are machined directly into the cast-iron cylinder head and are induction hardened to prevent wear.

Figure 31-7 Insert valve seats are a separate part that is interference fitted to a counterbore in the cylinder head.

Valve Fault Diagnosis Insert Seats Poor valve seating Causes include: too small a valve lash, hard carbon deposits, valve stem deposits, excessive valve stem-to-guide clearances, out-of-square valve guide and seat

Valve Fault Diagnosis Insert Seats Causes of valve seat recession include: improper valve lash adjustments on solid lifter engines, misadjustments on a valve train using hydraulic lifters

Figure 31-8 Typical intake valve seat wear.

Valve Fault Diagnosis Carbon Deposits Large clearance between the valve stem and guide or faulty valve stem seals allow too much oil into the stem which increases deposits

Valve Fault Diagnosis Carbon Deposits The valve cocks or leans sideways, which keeps the valve from seating properly causing it to leak and burn the valve face

Figure 31-9 Carbon deposits on the intake valve are often caused by oil getting past the valve stems or fuel deposits.

Figure 31-10 Excessive wear of the valve stem or guide can cause the valve to seat in a cocked position.

Valve Fault Diagnosis Excessive Temperatures Occur when the valve does not seat properly Root causes include: Cooling system passages in the head may be partially blocked by faulty casting or by deposits built up from the coolant Preignition and by detonation resulting from abnormal combustion

Figure 31-11 Valve face guttering caused by thermal shock.

Valve Fault Diagnosis Valve Seat Erosion Without leaded gasoline, the valve movement against the seat tears away tiny iron oxide particles which act like valve grinding compound, cutting into the valve seat surface

Valve Fault Diagnosis High Velocity Seating Indicated by excessive valve face wear, valve seat recession, and impact failure Caused by excessive lash in mechanical lifters and by collapsed hydraulic lifters

Valve Fault Diagnosis High Velocity Seating Impact breakage may occur under the valve head or at the valve keeper grooves

Valve Fault Diagnosis High Velocity Seating Impact breakage may also cause the valve head to fall into the combustion chamber ruining the piston before the engine can be stopped Described by several terms, including: Sucking a valve

Valve Fault Diagnosis High Velocity Seating Impact breakage may also cause the valve head to fall into the combustion chamber ruining the piston before the engine can be stopped Described by several terms, including: Dropping a valve

Valve Fault Diagnosis High Velocity Seating Impact breakage may also cause the valve head to fall into the combustion chamber ruining the piston before the engine can be stopped Described by several terms, including: Swallowing a valve

Figure 31-12 Note the broken piston caused by a valve breaking from the stem.

Valve Springs Purpose and Function Holds valve against the seat when the valve is not being opened

Valve Springs Spring Materials and Design Single inexpensive valve spring Made of chromium vanadium alloy steel

Valve Springs Spring Materials and Design Some use a flat coiled damper inside the spring to help reduce valve seat wear Normal valve springs wind up as they are compressed ?

Figure 31-13 A retainer and two split keepers hold the spring in place on the valve. A spring seat is used on aluminum heads. Otherwise, the spring seat is a machined area in the head.

Figure 31-14 Valve spring types ( left to right ): coil spring with equally spaced coils; spring with damper inside spring coil; closely spaced spring with a damper; taper wound coil spring.

Figure 31-15 Valve springs maintain tension in the valve train when the valve is open to prevent valve float, but must not exert so much tension that the cam lobes and lifters begin to wear.

Valve Springs Variable Rate Springs Also called progressive rate or variable pitch springs Uneven spacing between the coils Spring rates vary depending on compression

Valve Springs Variable Rate Springs Provides a low seat pressure while still providing the rate needed for high lift camshaft designs Helps control valve surge

Valve Springs Valve Spring Inspection Checked for squareness by rotating on a flat surface with a square held against the side Should measure within 1/16 in. (1.6 mm) of being square

Valve Springs Valve Spring Inspection Out-of-square springs are replaced Square springs should be checked to determine compressed force Surge damper is often specified to be removed when checking the spring force

Valve Springs Valve Spring Inspection A valve spring scale is used to measure the valve spring force at a specific height measurement (torque wrench on a lever system can also be used)

Valve Springs Valve Spring Inspection Valve springs are checked for the following: Free height (or length) without being compressed, should be within 1/16 (0.06) in. of specifications.

Valve Springs Valve Spring Inspection Valve springs are checked for the following: Pressure with valve closed and height as per specifications

Valve Springs Valve Spring Inspection Valve springs are checked for the following: Pressure with valve open and height as per specifications

Valve Springs Valve Spring Inspection Variations of plus or minus 10% from the published figures are usually acceptable

Figure 31-16 All valve springs should be checked for squareness by using a square on a flat surface and rotating the spring while checking. The spring should be replaced if more than 1/16 in. (1.6 mm) is measured between the top of the spring and the square.

Figure 31-17 One popular type of valve spring tester used to measure the compressed force of valve springs. Specifications usually include (1) free height (height without being compressed), (2) pressure at installed height with the valve closed, and (3) pressure with the valve open to the height specified.

Valve Keepers and Rotators Valve Keepers Used on the end of the valve stem to retain the spring Inside surfaces use a variety of grooves or beads

Valve Keepers and Rotators Valve Keepers Outside fits into a cone-shaped seat in the center of the valve spring retainer

Figure 31-18 Valve keepers (also called locks) are tapered so they wedge into a tapered hole in the retainer.

Valve Keepers and Rotators Valve Rotators Built-in devices in some valve spring retainers Cause controlled valve rotation as the valve is opened

Valve Keepers and Rotators Valve Rotators Purposes and Functions: Help prevent carbon buildup from forming

Valve Keepers and Rotators Valve Rotators Purposes and Functions: Reduce hot spots on the valves

Valve Keepers and Rotators Valve Rotators Purposes and Functions: Help to even out the wear on the valve face and seat

Valve Keepers and Rotators Valve Rotators Purposes and Functions: Improve valve guide lubrication

Valve Keepers and Rotators Valve Rotators Two types: Free rotators Positive rotator

Figure 31-19 Notice that there is no gap between the two keepers (ends butted together). As a result, the valve is free to rotate because the retainer applies a force, holding the keepers in place but not tight against the stem of the valve. Most engines, however, do not use free rotators and, therefore, have a gap between the keepers.

Figure 31-20 Type of valve rotator operation. Ball-type operation is on the left and spring-type operation is on the right.

VALVE RECONDITIONING PROCEDURE

Valve Reconditioning Procedure Usually called a “valve job” Can be performed using the following sequence: Stem is lightly ground and chamfered (called truing the valve tip)

Valve Reconditioning Procedure Can be performed using the following sequence: Face is ground to the proper angle using a valve grinder

Valve Reconditioning Procedure Can be performed using the following sequence: Seat is ground in the head Valve spring installed height and valve stem height are checked and corrected as necessary

Valve Reconditioning Procedure Can be performed using the following sequence: After a thorough cleaning, the cylinder head should be assembled with new valve stem seals installed

Valve Face Grinding Purpose and Function For best results perform the following: Slowly feed rotating grinding wheel to the rotating valve face

Valve Face Grinding Purpose and Function For best results perform the following: Move valve back and forth across the grinding wheel face

Valve Face Grinding Purpose and Function For best results perform the following: Do not feed the valve into the grinding stone more than 0.001 to 0.002 in. at one time

Valve Face Grinding Purpose and Function For best results perform the following: The valve is never moved off the edge of the grinding wheel

Valve Face Grinding Purpose and Function CAUTION: Safety glasses should always be worn for valve and seat reconditioning work. During grinding operations, fine hot chips fly from the grinding stones.

Valve Face Grinding Purpose and Function NOTE: Some valve grinders use the end of the valve to center the valve while grinding. If the tip of the valve is not square with the stem, the face of the valve may be ground improperly.

Figure 31-21 Resurfacing the face of a valve. Both the valve and the grinder stone or disc are turned to ensure a smooth surface finish on the face of the valve.

Valve Face Grinding Margin Distance between the head and the seat of the valve Should be 0.03 in. (0.8 mm)

Valve Face Grinding Margin Some manufacturers specify a minimum margin of less than 0.03 in. for some engines, especially intake valves

Valve Face Grinding Margin NOTE: To help visualize a 0.03 in. margin, note that this dimension is equal to about 1/32 in. or the thickness of a U.S. dime.

Figure 31-22 Never use a valve that has been ground to a sharp edge. This weakens the valve and increases the chance of valve face burning.

Valve Seat Reconditioning Purpose and Function Valve seats are reconditioned at the following times: After the cylinder head has been properly cleaned, resurfaced, and the valve guides have been resized or reconditioned

Valve Seat Reconditioning Purpose and Function Valve seats are reconditioned at the following times: When the valve guides have been replaced

Valve Seat Reconditioning Valve Seat Angles Normal seat angle of either 45 or 30 degrees 45 degrees is most commonly used

Valve Seat Reconditioning Valve Seat Angles 30 degrees is usually used on intake valves only

Figure 31-24 Grinding a 45-degree angle establishes the valve seat in the combustion chamber.

Valve Seat Reconditioning Interference Angle Valve is often ground with a face angle 1 degree less than the seat angle to compensate for the change in hot seating

Valve Seat Reconditioning Interference Angle Makes a positive seal at the combustion chamber edge of the seat when the engine is first started after a valve job

Figure 31-25 Some vehicle manufacturers recommend that the valve face be resurfaced at a 44-degree angle and the valve seat at a 45-degree angle. This 1-degree difference is known as the interference angle.

Valve Seat Reconditioning Valve Seat Width Width increases with resurfacing Resurfaced seats must be narrowed

Valve Seat Reconditioning Valve Seat Width Valve seat width and the contact with the valve face should match the manufacturer’s specifications

Figure 31-26 The seat must contact evenly around the valve face. For good service life, both margin and overhang should be at least 1/32 in. (0.8 mm).

Valve Seat Reconditioning Three-Angle Valve Job Valve seats are ground three times First angle: angle of the valve seat specified by the vehicle manufacturer, usually 45 degrees

Valve Seat Reconditioning Three-Angle Valve Job Valve seats are ground three times Second angle (throating angle): 60-degree stone or cutter used to remove material right below the valve seat

Valve Seat Reconditioning Three-Angle Valve Job Valve seats are ground three times Third angle (topping angle): 30-degree stone or cutter used to smooth the transition between the valve seat and the cylinder head

Figure 31-27 Grinding a 60-degree angle removes metal from the bottom to raise and narrow the seat.

Figure 31-28 Grinding a 30-degree angle removes metal from the top to lower and narrow the seat.

Figure 31-29 A typical three-angle valve job using 30-, 45-, and 60-degree stones or cutters.

Valve Guide Pilots Types of Pilots Tapered pilots Expandable pilots

Valve Guide Pilots NOTE: If the guide is not reconditioned, the valve will match the seat when an expandable pilot is used.

Figure 31-30 A valve guide pilot being used to support a valve seat cutter.

Valve Seat Grinding Stones Types of Stones Roughing stone Finishing stone Hard seat stone

Valve Seat Grinding Stones NOTE: Stellite ® is a nonmagnetic hard alloy used for valve seats in heavy-duty applications.

Valve Seat Grinding Stones Dressing the Grinding Stone Give it a clean, sharp cutting surface Stone installed on holder

Valve Seat Grinding Stones Dressing the Grinding Stone Holder and stone assembly rotated with driver Diamond is adjusted to touch stone face

Valve Seat Grinding Stones Dressing the Grinding Stone Diamond dressing tool moved slowly across stone's face Redressing is necessary Each time a stone is placed on a holder

Valve Seat Grinding Stones Dressing the Grinding Stone Redressing is necessary At beginning of each valve job

Valve Seat Grinding Stones Dressing the Grinding Stone Redressing is necessary Any time stone is not cutting smoothly and cleanly

Valve Seat Grinding Stones Grinding the Valve Seat Clean valve seat before grinding Place pilot in valve guide and put drop of oil on its end

Valve Seat Grinding Stones Grinding the Valve Seat Place holder over the pilot Grind in short bursts, checking for proper grinding after each burst

Valve Seat Grinding Stones Grinding the Valve Seat Lift holder and stone from seat between each grinding burst to check condition of seat

Valve Seat Grinding Stones Grinding the Valve Seat Check seat with a dial indicator gauge to make sure that it is concentric within 0.002 in. (0.05 mm) before finishing seat

Valve Seat Grinding Stones Grinding the Valve Seat Total indicator runout (TIR) - maximum acceptable variation (0.002 in.)

Figure 31-31 Checking valve seat concentricity using a dial indicator.

Figure 31-32 Typical dial indicator type of micrometer for measuring valve seat concentricity.

Valve Seat Grinding Stones Narrowing the Valve Seat Generally accepted seat widths are as follows: For intake valves: 1/16 in. or 0.0625 in. (about the thickness of a nickel) (1.5 mm)

Valve Seat Grinding Stones Narrowing the Valve Seat Generally accepted seat widths are as follows: For exhaust valves: 3/32 in. or 0.0938 in. (about the thickness of a dime and a nickel together) (2.4 mm)

Valve Seat Grinding Stones Narrowing the Valve Seat Using a 30-degree topping stone (for a 45-degree seat) lowers the upper outer edge and narrows the seat

Valve Seat Grinding Stones Narrowing the Valve Seat Using a 60-degree throating stone raises the lower inner edge and narrows the seat

Valve Seat Grinding Stones Narrowing the Valve Seat Using a 45-degree stone widens the seat

Figure 31-33 After the valve face and the valve seat are ground (reconditioned), lapping compound is used to smooth the contact area between the two mating surfaces. Notice that the contact is toward the top of the face. For maximum life, the contact should be in the middle of the face.

Valve Seat Cutters Advantages of using a seat cutter compared to a grinding stone include: A number of cutting blades are secured at the correct seat angle in the cutting head of this valve seat reconditioning tool.

Valve Seat Cutters Advantages of using a seat cutter compared to a grinding stone include: The cutter angle usually includes the interference angle so that new valves with standard valve face angles can be used without grinding the new valve face.

Valve Seat Cutters Advantages of using a seat cutter compared to a grinding stone include: The cutters do not require dressing as stones do. The cutter is rotated by hand or by using a special speed reduction motor. Only metal chips are produced.

Valve Seat Cutters Advantages of using a seat cutter compared to a grinding stone include: The finished seat is checked for concentricity and fit against the valve face.

Valve Seat Cutters CAUTION: A cutter should only be rotated clockwise. If a cutter is rotated counterclockwise, damage to the cutting surfaces ruins the cutter.

Valve Seat Testing Purpose Valves should be inspected for proper sealing and to ensure that the valve seat is concentric with the valve face

Figure 31-34 A cutter is used to remove metal and form the valve seat angles.

Valve Seat Testing Methods Vacuum testing can be done by applying vacuum to the intake and/or exhaust port using a tight rubber seal and a vacuum pump

Valve Seat Testing Methods Ports or chamber can be filled with mineral spirits or some other suitable fluid. A good seal should not leak fluid for at least 45 seconds.

Valve Seat Testing Methods Valve seating can be checked by applying air pressure to the combustion chamber and checking for air leakage past the valve seat

Valve Seat Testing Methods The valves can be lapped using valve grinding compound and looking at the “parting line” between the valve face on the valve and the valve seat in the cylinder head

Valve Seat Replacement Purpose Valve seats need to be replaced if they are cracked, burned, or eroded too much to be reground

Valve Seat Replacement Purpose Replacement is accomplished by using a pilot in the valve guide Valve guide must be reconditioned before the seat can be replaced

Figure 31-35 All aluminum cylinder heads use valve seat inserts. If an integral valve seat (cast-iron head) is worn, it can be replaced with a replacement valve seat by machining a pocket (counterbore) to make a place for the new insert seat.

Valve Seat Replacement Insert Seat Removal Methods Small pry bars can be used to snap the seat from the counterbore Easier to do this if the old seat is drilled to weaken it

Valve Seat Replacement Insert Seat Removal Methods Expandable hook-type puller can be used to remove the seat insert

Valve Seat Replacement Type of Valve Seats Cast iron Stainless steel Nickel cobalt Powdered metal (PM)

Figure 31-36 Insert valve seats are rings of metal driven into the head.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 1: The cutting tool is positioned securely in the tool holder so that it will cut the counterbore at the correct diameter.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 2: The tool holder is attached to the size of pilot that fits the valve guide. The tool holder feed mechanism is screwed together so that it has enough threads to properly feed the cutter into the head. This assembly is placed in the valve guide so that the cutting tool rests on the seat that is to be removed.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 3: The new insert is placed between the support fixture and the stop ring. The stop ring is adjusted against the new insert so that cutting will stop when the counterbore reaches the depth of the new insert.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 4: The boring tool is turned by hand or with a reduction gear motor drive. It cuts until the stop ring reaches the fixture.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 5: The support fixture and the tool holder are removed. The pilot and the correct size of adapter are placed on the driving tool.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 6: The seats should be cooled with dry ice to cause them to shrink. Each insert should be left in the dry ice until it is to be installed. This will allow it to be installed with little chance of metal being sheared from the counterbore. Sheared chips could become jammed under the insert, keeping it from seating properly. The chilled seat is placed on the counterbore.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 7: The driver with a pilot is then quickly placed in the valve guide so that the seat will be driven squarely into the counterbore. The driver is hit with a heavy hammer to seat the insert.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 8: Heavy blows are used to start the insert, and lighter blows are used as the seat reaches the bottom of the counterbore.

Valve Seat Replacement Replacing an Integral Valve Seat STEP 9: The installed valve seat insert is peened in place by running a peening tool around the metal on the outside of the seat. The peened metal is slightly displaced over the edge of the insert to help hold it in place.

Valve Stem Height Definition Distance the valve stem is above the spring seat. Valve stem height is important to maintain for all engines (especially overhead camshaft engines).

Valve Stem Height Definition When the valve seat and the valve face are ground, the valve stem extends deeper into the combustion chamber and extends higher or farther into the cylinder head.

Valve Stem Height Definition The valve is put in the head, and the length from the tip to the valve spring seat is measured. The tip is ground to shorten the valve stem length to compensate for the valve face and seat grinding.

Valve Stem Height Definition The valve will not close if the valve tip extends too far from the valve guide on engines that have hydraulic lifters and nonadjustable rocker arms.

Valve Stem Height Definition If the valve is too long, the tip may be ground by as much as 0.02 in. (0.5 mm) to reduce its length. If more grinding is required, the valve must be replaced. If it is too short, the valve face or seat may be reground, within limits, to allow the valve to seat deeper.

Valve Stem Height Definition Where excessive valve face and seat grinding has been done, shims can be placed under the rocker shaft on some engines as a repair to provide correct hydraulic lifter plunger centering. These shims must have the required lubrication holes to allow oil to enter the shaft.

Figure 31-37 Valve stem height is measured from the spring seat to the tip of the valve after the valve seat and valve face have been refinished. If the valve stem height is too high, up to 0.02 in. can be ground from the tips of most valves.

Installed Height Definition Distance between the valve spring seat and the underside of the valve spring retainer

Installed Height Correcting Installed Height Special valve spring spacers, inserts, or shims, called valve spring inserts (VSI) are installed under the valve springs to restore original tension Valve springs available in three thicknesses: 0.015 in. (0.38 mm)

Installed Height Correcting Installed Height Valve springs available in three thicknesses: 0.03 in. (0.75 mm) 0.06 in. (1.5 mm)

Installed Height Correcting Installed Height To determine the exact thickness of insert to install, measure the valve spring installed height

Installed Height Correcting Installed Height If the installed height is greater than specifications, select the valve spring insert (shim) that brings the installed height to within specifications

Installed Height Correcting Installed Height CAUTION: Do not use more than one valve spring insert. If the correct installed height cannot be achieved using one insert, replace the valve seat to restore the proper installed height.

Figure 31-38 Installed height is determined by measuring the distance from the spring seat to the bottom of the valve spring retainer.

Figure 31-39 Valve spring inserts are used to restore proper installed height.

Valve Stem Seals Purpose and Function Used on the exhaust valve, because a weak vacuum in the exhaust port area can draw oil into the exhaust stream

Valve Stem Seals Purpose and Function Used in overhead valve engines to control the amount of oil used to lubricate the valve stem as it moves in the guide

Figure 31-40 Engine vacuum can draw oil past the valve guides and into the combustion chamber. The use of valve stem seals limits the amount of oil that is drawn into the engine. If the seals are defective, excessive blue (oil) smoke is most often observed during engine start-up.

Figure 31-41 Engine oil can also be drawn past the exhaust valve guide because of a small vacuum created by the flow of exhaust gases. Any oil drawn past the guide would simply be forced out through the exhaust system and not enter the engine. Some engine manufacturers do not use valve stem seals on the exhaust valves.

Valve Stem Seals Types of Valve Stem Seals Umbrella valve stem seal O-ring valve stem seal Positive valve stem seal

Valve Stem Seals Valve Seal Materials Nitrile (Nitril) Polyacrylate Viton

Figure 31-42 Umbrella seals install over the valve stems and cover the guide.

Figure 31-43 A small square cut O-ring is installed under the retainer in a groove in the valve under the groove(s) used for the keepers (locks).

Figure 31-44 Positive valve stem seals are the most effective type because they remain stationary on the valve guide and wipe the oil from the stem as the valve moves up and down.

Figure 31-45 The positive valve stem seal is installed on the valve guide.

Figure 31-46 An assortment of shapes, colors, and materials of positive valve stem seals.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 1: Clean the reconditioned cylinder head thoroughly with soap and water to wash away any remaining grit and metal shavings from the valve grinding operation.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 2: Valves are assembled in the head, one at a time. The valve guide and stem are given a liberal coating of engine oil, and the valve is installed in its guide.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 3: Umbrella and positive valve stem seals are installed. Push umbrella seals down until they touch the valve guide. Use a plastic sleeve over the tip of the valve when installing positive seals to prevent damage to the seal lip. Make sure that the positive seal is fully seated on the valve guide and that it is square.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 4: Hold the valve against the seat as the valve spring seat or insert, valve spring, valve seal, and retainer are placed over the valve stem. One end of the valve spring compressor pushes on the retainer to compress the spring. Install the valve spring seat if assembling an aluminum head.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 5: The O-ring type of valve stem seal, if used, is installed in the lower groove. The valve keepers are installed while the valve spring is compressed. Using grease helps to keep them attached to the valve stem as the valve spring compressor is released.

Installing the Valves Procedure Assembling a cylinder head includes the following steps: STEP 6: Release the valve spring compressor slowly and carefully while making sure that the valve keepers seat properly between the valve stem grooves and the retainer.

INSTALLING A NEW VALVE SEAT 1 After the valve guide has been replaced or checked for being within specification, insert a pilot into the valve guide.

INSTALLING A NEW VALVE SEAT 2 Level the bubble on the pilot by moving the cylinder head, which is clamped to a seat/guide machine.

INSTALLING A NEW VALVE SEAT 3 Select the proper guide for the application. Consult guide manufacturer’s literature for recommendations.

INSTALLING A NEW VALVE SEAT 4 Select the correct cutter and check that the cutting bits are sharp.

INSTALLING A NEW VALVE SEAT 5 Carefully measure the exact outside diameter (O.D.) of the valve seat.

INSTALLING A NEW VALVE SEAT 6 Adjust the depth of the cutter bit to achieve the specified interference fit for the valve seat.

INSTALLING A NEW VALVE SEAT 7 Install the pilot into the valve guide to support the seat cutter.

INSTALLING A NEW VALVE SEAT 8 Install the seat cutter onto the pilot.

INSTALLING A NEW VALVE SEAT 9 Adjust the depth of cut, using the new valve seat to set it to the same depth as the thickness of the seat.

INSTALLING A NEW VALVE SEAT 10 With the cylinder head still firmly attached to the seat and guide machine, start the cutter motor and cut the head until it reaches the stop.

INSTALLING A NEW VALVE SEAT 11 The finish cut valve seat pocket. Be sure to use a vacuum to remove all of the metal shavings from the cutting operation.

INSTALLING A NEW VALVE SEAT 12 Place the chilled valve seat over the pilot being sure that the chamfer is facing toward the head as shown.

INSTALLING A NEW VALVE SEAT 13 Install the correct size driver onto the valve seat.

INSTALLING A NEW VALVE SEAT 14 Using the air hammer or press, press the valve seat into the valve pocket.

INSTALLING A NEW VALVE SEAT 15 A new valve seat is now ready to be machined or cut.

TECH TIP Hot Engine + Cold Weather = Trouble Serious valve damage can occur if cold air reaches hot exhaust valves soon after the engine is turned off. An engine equipped with exhaust headers and/or straight-through mufflers can allow cold air a direct path to the hot exhaust valve. The exhaust valve can warp and/or crack as a result of rapid cooling. BACK TO PRESENTATION This can easily occur during cold windy weather when the wind can blow cold outside air directly up the exhaust system. Using reverse-flow mufflers with tailpipes and a catalytic converter reduces the possibilities of this occurring.

WARNING If a sodium-filled valve is damaged and the sodium leaks out, it can cause a fire if exposed to water. Sodium reacts violently when exposed to water and burns uncontrollably. BACK TO PRESENTATION

TECH TIP Valve Seat Recession and Engine Performance If unleaded fuel is used in an engine without hardened valve seats, valve seat recession is likely to occur over time. Without removing the cylinder heads, how can a technician identify valve seat recession? BACK TO PRESENTATION As the valve seat wears up into the cylinder head, the valve itself also is located farther up in the head. As this wear occurs, the valve clearance (lash) decreases. If hydraulic lifters are used on the engine, this wear will go undetected until the reduction in valve clearance finally removes all clearance (bottoms out) in the lifter. When this occurs, the valve does not seat fully, and compression, power, and fuel economy are drastically reduced. With the valve not closing completely, the valve cannot release its heat and will burn or begin to melt. If the valve burns, the engine will miss and not idle smoothly. If solid lifters are used on the engine, the decrease in valve clearance will first show up as a rough idle only when the engine is hot. As the valve seat recedes farther into the head, low power, rough idle, poor performance, and lower fuel economy will be noticed sooner than if the engine were equipped with hydraulic lifters. To summarize, refer to the following symptoms as valve seat recession occurs. 1. Valve lash (clearance) decreases (valves are not noisy). 2. The engine idles roughly when hot as a result of reduced valve clearance. To summarize, refer to the following symptoms as valve seat recession occurs. 3. Missing occurs, and the engine exhibits low power and poor fuel economy, along with a rough idle, as the valve seat recedes farther into the head. 4. As valves burn, the engine continues to run poorly; the symptoms include difficulty in starting (hot and cold engine), backfiring, and low engine power. HINT: If valve lash is adjustable, valve burning can be prevented by adjusting the valve lash regularly. Remember, as the seat recedes, the valve itself recedes, which decreases the valve clearance. Many technicians do not think to adjust valves unless they are noisy. If, during the valve adjustment procedure, a decrease in valve lash is noticed, then valve seat recession could be occurring.

FREQUENTLY ASKED QUESTION What Is Valve Float? Valve float occurs when the valve continues to stay open after the camshaft lobe has moved from under the lifter. This happens when the inertia of the valve train overcomes the valve spring tension at high engine speeds. ? BACK TO PRESENTATION Figure 31-15 Valve springs maintain tension in the valve train when the valve is open to prevent valve float, but must not exert so much tension that the cam lobes and lifters begin to wear.

TECH TIP Grinding the Valves for More Power A normal “valve job” includes grinding the face of the valve to clean up any pits and grinding the valve stems to restore the proper stem height. However, a little more airflow in and out of the cylinder head can be accomplished by performing two more simple grinding operations. BACK TO PRESENTATION Use the valve grinder and adjust to 30 degrees (for a 45-degree valve) and grind a transition between the valve face and the valve stem area of the valve. While this step may reduce some desirable swirling of the air-fuel mixture at lower engine speeds, it also helps increase cylinder filling, especially at times when the valve is not fully open. Chamfer or round the head of the valve between the top of the valve and the margin on the side. By rounding this surface, additional airflow into the cylinder is achieved. Figure 31-23 After grinding the 45-degree face angle, additional airflow into the engine can be accomplished by grinding a transition between the face angle and the stem, and by angling or rounding the transition between the margin and the top of the valve.

TECH TIP The MIG Welder Seat Removal Trick A quick and easy method to remove insert valve seats is to use a metal inert gas (MIG) welder, also called a gas metal arc welder (GMAW). After the valve has been removed, use the MIG welder and lay a welding bead around the seat area of the insert. BACK TO PRESENTATION As the welder cools, it shrinks and allows the insert to be easily removed from the cylinder head. The weld bead also provides a surface that can be used to pry the seat from the cylinder head.

TECH TIP Use the Recommended Specifications A technician replaced valve seat inserts in an aluminum cylinder head. The factory specification called for a 0.002 in. interference fit (the insert should be 0.002 in. larger in diameter than the seat pocket in the cylinder head). Shortly after the engine was started, the seat fell out, ruining the engine. BACK TO PRESENTATION The technician should have used the interference fit specification supplied with the replacement seat insert. Interference fit specifications depend on the type of material used to make the insert. Some inserts for aluminum heads require as much as 0.007 in. interference fit. Always refer to the specification from the manufacturer of the valve inserts when replacing valve seats in aluminum cylinder heads.

TECH TIP Purchase Engine Parts from a Known Manufacturer It is interesting to note that an automotive service technician cannot tell the difference between these synthetic rubber valve stem seals if they have come out of the same mold For the same engine. BACK TO PRESENTATION Often suppliers that package gasket sets for sale at a low price will include low-temperature Nitrile, even when the engine needs higher-temperature polyacrylate. The best chances of getting the correct valve stem seal material for an engine is to purchase gaskets and seals packaged by a major brand gasket company.

TECH TIP Check Before Bolting It On Using new assembled cylinder heads, whether aluminum or cast iron, is a popular engine buildup option. However, experience has shown that metal shavings and casting sand are often found inside the passages. Before bolting on these “ready to install” heads, disassemble them and clean all passages. BACK TO PRESENTATION Often machine shavings are found under the valves. If this debris were to get into the engine, the results would be extreme wear or damage to the pistons, rings, block, and bearings. This cleaning may take several hours, but how much is your engine worth?

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