Automotive Upper End Theory + Service--part 6

VALVE GUIDE RECONDITIONING

Valve guide problems can be lumped into one of three basic categories: inadequate lubrication, valve geometry problems, and wrong valve stem-to-guide clearance.

Inadequate lubrication can be caused by oil starvation in the upper valve train due to low oil pressure, obstructed oil passages, improper operation of push rods, and using the wrong type of valve seal. Insufficient lubrication results in stem scuffing, rapid stem and guide wear, possible valve sticking, and ultimately valve failure due to poor seating and overheating.

Geometry problems include an incorrectly installed valve height, off-square springs, and rocker arm tappet screws or rocker arms that push the valve sideways every time it opens. This causes uneven guide wear, leaving an egg-shaped hole. The wear leads to increased stem-to-guide clearance, poor valve seating, and premature valve failure.

A certain minimum amount of clearance is needed for lubrication and thermal expansion of the valve stem. Exhaust valves require more clearance than intakes because they run hotter. Clearance should also be close enough to prevent a buildup of varnish and carbon deposits on the stems, which could cause sticking. Insufficient clearance, however, can lead to rapid stem and guide wear, scuffing, and sticking, which prevents the valve from seating fully. This, in turn, causes the valve to run hot and burn.

Fgr__63 Measuring valve stem installed height. Valve stem installed height Spring seat

Fgr__64 Valve guide wear can be measured with a small-hole gauge and a micrometer. Small-hole gauge Take measurement in three places

Fgr__65 Checking for valve guide wear with a dial indicator. Dial indicator

Valve Guide Wear:

The amount of valve guide wear can be measured with a ball (small-bore) gauge and micrometer. Insert and expand the ball gauge at the top of the guide. Lock it to that diameter, remove it from the guide, and measure the ball gauge with an outside micrometer.

Repeat this process with the ball gauge in the middle and the bottom of the guide (64). Compare your measurements to the specifications for valve guide inside diameter. Then compare your measurements against each other. Any difference in reading shows a taper or wear inside the guide.

Another way to check for excessive guide wear is with a dial indicator. The accuracy of this check is directly dependent on the amount the valve is open during the check. Some manufacturers specify this amount or provide special spacers that are installed over the valve stem to ensure the proper height. Attach the dial indicator to the cylinder head and position it so the plunger is at a right angle to the valve stem being measured (65). With the plunger in contact with the valve head, move the valve toward the indicator and set the dial indicator to zero. Now move the valve from the indicator. Observe the reading on the dial while doing this. The reading on the indicator is the total movement of the valve and is indicative of the guide's wear. Compare the reading to specifications.

If the clearance is too great, oil can be drawn past both the intake and exhaust guides. Though oil consumption is more of a problem with sloppy or worn intake guides because the guides are constantly exposed to vacuum, oil can also be pulled down the exhaust guides by suction created in the exhaust port.

The outflow of hot exhaust creates a venturi effect as it exits the exhaust port, creating enough vacuum to draw oil down a worn guide (66).

Because it retains oil well, the antiseize and anti wear characteristics of bronze allow a bronze guide to last two to five times longer than a cast-iron guide.

Knurling:

Knurling is one of the fastest ways to restore the inside diameter (ID) of a worn valve guide. The process raises the surface of the guide ID by plowing tiny fur rows through the surface of the metal (67). As the knurling tool cuts into the guide, metal is raised or pushed up on either side of the indentation. This effectively decreases the ID of the guide hole. A burnisher is used to press the ridges flat and is then used to shave off the peaks of these ridges to produce the proper-sized hole and restore the correct guide-to stem clearance.

One of the main advantages of knurling is that it does not change the centerline of the valve stem.

Knurling also allows a rebuilder to reuse the old valve if wear is within acceptable limits, helping to reduce rebuilding costs. In spite of its speed and simplicity, knurling is not a cure for badly worn guides.

Reaming and Oversized Valves--Reaming increases the guide hole size to take an oversize valve stem or restores the guide to its original diameter after installing inserts or knurling.

When reaming, limit the amount of metal removed per pass. Always reface the valve seat after the valve guide has been reamed and use a suitable scraper to break the sharp corner (ID) at the top and bottom of the valve guide.

The advantage of reaming for an oversized valve is that the finished product is totally new. The guide is straight, the valve is new, and the clearance is accurate. The use of oversized valve stems is generally considered to be superior to knurling. Yet, like knurling, it’s relatively quick and easy. The only tool required is a reamer. Its use is limited to heads in which the guides are not worn beyond the limits of the available oversize valves.

Thin-Wall Guide Liners:

Thin-wall guide liners (68) are often inserted into guides to restore them. They provide the benefits of a bronze guide surface. They can be used in integral and replaceable guides. It’s faster, easier, and cheaper than installing new guides in heads with replaceable or integral guides, and it maintains guide centering with respect to the seats.

Fgr__66 (A) Worn intake guides allow the intake vacuum to suck oil down the guide, and (B) worn exhaust guides can do the same.

Fgr__67 Knurling restores the inside diameter (ID) dimensions of a worn valve guide by raising the inside surface of the guide by plowing tiny furrows through the surface of the metal.

Fgr__68 A thin-wall valve guide liner.

Phosphor-bronze or silicon-aluminum-bronze are used to make the liners. They are designed for a 0.002- to 0.0025-inch (0.0508 to 0.0635 mm) press-fit.

A tight fit is necessary for proper heat transfer and to prevent the liner from working loose.

The original guides are bored to the required diameter for the liner. The liner is then pressed into the bore. It’s important to note that some liners are not precut to the length of the original guide. When this is the case, the liner should be cleanly cut or milled to the correct length before installing it. After installation, guide-to-valve stem clearance should be checked and corrected by reaming or knurling.

Valve Guide Replacement--Replacing the valve guide is a repair option. However, pressing out the old guides and installing new ones can be difficult on aluminum heads. Cracking the head or galling the guide hole is always a risk.

Integral Guides--To replace integral guides, bore the old guide out. The bore should allow for an interference fit of about 0.002 inch (0.0508 mm). Most technicians freeze the guides before attempting to install them. Lubricate the guide and press or drive it into the bore in the head. It’s important to keep the guide straight while it’s being installed.

Occasionally, the new guide won’t be concentric with the valve seat. Install a new seat to correct the problem, and check the concentricity of the valve seat with a concentricity gauge (69).

Insert Guides--To press out an old valve guide, place a proper-sized driver so that its end fits snugly into the guide. The shoulder on the driver must also be slightly smaller than the OD of the guide. Use a heavy ball peen hammer to drive the guide out of the cylinder head.

This procedure should be done with care. There is always the danger of breaking the guide or damaging the guide bore in the head. Cast-iron guides in particular have a tendency to gall aluminum heads. If the bore becomes damaged, it must be re-bored and an oversized guide installed. To help prevent these problems, freeze and lubricate the guides before installation. Also, use a press and the correct driver to install them. Keep the guide aligned in its bore and press straight down, not at an angle. If one end of the guide is cut at an angle, make sure the angle is properly placed within the valve port.

Valve Guide Height: Guide height is important to avoid interference with the valve spring retainer.

The manufacturer's specifications give the correct valve guide installed height, but it’s wise to measure the height of the old guides and use this as a reference. As each guide is installed, the installed height should be measured. As each guide is installed, insert a valve. Check for any stem interference.

RECONDITIONING VALVE SEATS

To ensure proper seating of the valve, the valve seat must be the correct width (70), in the correct location on the valve face, and concentric with the guide (less than 0.002-inch [0.0508 mm] runout).

The ideal seat width is 1/16 inch for intake valves and 3/32 inch (2.38 mm) for exhaust valves. This width ensures proper sealing and heat transfer. However, when an existing seat is refinished to make it smooth and concentric, it also becomes wider.

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Fgr__71 Using a prybar to remove a damaged insert seal.

Fgr__72 Using an outside micrometer to expand the cutter head to allow for an interference fit between the bore and the new valve seat.

Fgr__73 The valve to openings of this head has been bored and is ready for new seat inserts.

Fgr__74 Staking the valve seat to the head can be done with a sharp chisel.

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CAUTION! Wear the proper gloves when handling dry ice.

Seat: 45° Top: 30° Throat: 60° Fgr__75 The three angles of a properly finished seat.

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PROCEDURE

Insert Valve Seat Removal and Replacement

STEP 1 To remove the damaged insert, use a puller or a prybar (71).

STEP 2 After removal, clean up the counterbore or recut it to accommodate oversized inserts.

STEP 3 Insert the counterboring pilot into the valve guide.

Then mount the base and ball shaft assembly to the gasket face angle of the cylinder head.

STEP 4 Use an outside micrometer to accurately expand the cutterhead to a predetermined size of the counterbore (72). Remember that the counterbore should have a slightly smaller ID than the OD of the insert to provide for an interface fit.

STEP 5 Place the valve insert counterboring tool over the pilot and ball-shaft assembly. Preset the depth of the valve seat insert at the feed screw.

STEP 6 Cut the insert by turning the stop-collar until it reaches the present depth. Use a lubricant on the cutters for a smoother finish (73).

STEP 7 To install the insert, heat the head in a parts cleaning oven to approximately 350°F to 400°F (176°C to 204°C). Chill the insert in a freezer or with dry ice before installation.

STEP 8 Press the seat with the proper interference fit using a driver.

STEP 9 When the installation is complete, the edge around the outside of the insert is staked as shown in Fgr__74. By doing so, the insert will be secured more effectively in the counterbore.

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Wide seats cause problems. Seating pressure drops as seat width increases. Less force is available to crush carbon particles that stick to the seats, and seats run cooler, allowing deposits to build up on them.

The seat should contact the valve face 1/32 inch (0.79 mm) from the margin of the valve. When the engine reaches operating temperature, the valve expands slightly more than the seat. This moves the contact area down the valve face. Seats that make too low a contact with the valve face might lose partial contact at normal operating temperatures.

Valve seats can be reconditioned or repaired by one of two methods, depending on the seat type- machining a counterbore to install an insert seat, or grinding, cutting, or machining an integral seat.

Fgr__69 The centerline of the guide should be concentric with the seat.

Fgr__70 Checking valve seat width.

Cracked, heavily burnt, and loose seats should be replaced. If the seat is slightly blemished, it may only need to be refaced. Some rebuilders always replace the valve seats in an aluminum head when it’s being reconditioned. This helps restore correct valve height and valve train geometry. Also, many engines have powdered metal seats. These become harder through use and can be very difficult to machine. Therefore, they are replaced with new powder metal or alloy seats.

Valve seats can be reconditioned or repaired by machining a counterbore to install an insert seat, or grinding, cutting, or machining an integral seat.

Seats should not be serviced until all other machining or repairs have been done to the head and the head has been thoroughly cleaned. This includes the reconditioning of the valve guides.

Installing Valve Seat Inserts: The following steps outline a typical procedure for valve seat insert removal and replacement.

Reconditioning Integral Seats:

The average valve seat width is 0.060 inch (1.524 mm) and begins 0.030 inch (0.7620 mm) from the valve margin. A properly reconditioned seat has three angles: top, 30 or 15 degrees; seat, 45 or 30 degrees; and throat, 60 degrees. Using three angles provides the correct seat width and sealing position on the valve face (75).

Integral valve seats can be reconditioned by grinding, cutting, or machining.

Grinding Valve Seats-- When grinding a valve seat, it’s very important to use the correct size pilot and grind stone. Hard seats use a soft stone and soft seats (cast iron) use a harder stone.

The stone must be properly dressed and cutting oil used to aid in grinding.

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Fgr__76 Grinding the seat.

Fgr__77 A valve seat being cut at three angles at the same time. Jasper Engines & Transmissions

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SHOP TALK -- Before grinding, many technicians clean the seats by placing a piece of fine emery cloth between the stone and the seat and giving the surface a hard rub. This will help prevent contamination of the seat grinding stone by any oil or carbon residue that might be present on the valve seat. Such contamination could cause glazing.

The grinding wheel is positioned and centered by inserting a properly sized pilot shaft into the valve guide (76). All valve guide service must be completed before installing the pilot.

The seat is ground by continually and quickly raising and lowering the grinder unit on and off the seat.

Grinding should only continue until the seat is clean and free of defects.

Cutting Valve Seats

Cutting valve seats differs from grinding only in the equipment used (77). Hardened valve seat cutters replace grinding wheels. The basic seat cut ting procedures are the same as those for grinding.

Always check the fit of the valve face on the seat and adjust the seat as needed after initial cuts.

Checking Valve Fit:

While cutting a 45-degree or other specified seat, make the seat wider than specifications. Bevel or chamfer the top of the seat with a topping stone (normally 30 degrees). Then bevel the bottom with a throating stone (normally 60 degrees). Coat the face of the valve with machinist dye, which is a Prussian blue compound. Install the valve into its seat. Then open the valve and snap it closed against the seat several times. Remove the valve and look at the pattern on the valve face and seat.

The dye should show the face making full and even contact with the seat. The contact area should also be centered on the valve seat. If the pattern on the valve face is not even, the valve should be replaced. If the pattern on the seat is not even, check the concentricity of the guide and replace the guide and/or seat.

If the contact area is above the center of the seat, it needs to be lowered (78). Cut the seat with the topping stone. This stone will also make the seat narrower. If the contact area is too low, cut the seat with the throating stone. When using the topping or throating stone or cutting bits to move the contact area, remove a little metal and recheck the contact area. Keep machining the seat until the contact area is the correct width and has the desired placement.

After the contact area is acceptable, use the 45-degree stone to clean off any possible burrs caused by the cutting and grinding. Make sure all metal particles from machining the seat are totally removed before assembling the head.

Lapping: Some recommend lapping the valves after the seat area has been adjusted. This procedure uses an abrasive compound to remove all small imperfections in the contact area between the valve face and the seat.

The abrasive lapping compound is spread thinly over the face of the valve. With the face against the seat, the valve is moved back and forth with a lapping tool. A lapping tool is basically a stick with a suction cup on the end. The suction cup is placed on the outside of the valve head and the stick is rotated back and forth by hand. After several rotations, the valve is removed and its face and seat are wiped clean.

Fgr__78 The fit of the valve face in the seat should be checked carefully.

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Valve guide seal installer Valve seal Spring seat Valve spring

Valve retainer; Valve keepers

Intake valve seal - white spring Exhaust valve seal - black spring Note: Place the end of valve spring with closely wound coils towards the cylinder head.

Note: Install the valve spring seats before installing the valve seals.

Exhaust and intake valve seals are NOT interchangeable.

Fgr__79 Installation of a positive oil seal onto a valve guide.

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VALVE STEM SEALS

Valve stem seals are used to control the amount of oil allowed between the valve stem and the guide. The stems and guides will scuff and wear excessively if they don’t have enough lubrication. Too much oil produces heavy deposits that build up on the intake valve and hard deposits on the head end of the exhaust valve stem. Worn valve stem seals can increase the oil consumption by as much as 70%.

There are basically three types of seals. Positive seals fit tightly around the top of the guide and scrape oil off the valve stem as it moves up and down. Deflector, splash, or umbrella-type seals ride up and down on the valve stems to deflect oil away from the guides.

O-ring seals are used to prevent oil from moving into the guide when the valve is open.

Installing Positive Valve Seals

To install a positive valve seal (79), place the plastic sleeve in the kit over the end of the valve stem to protect the seal as it slides over the keeper grooves. Lightly lubricate the sleeve. Carefully place the seal on the cap over the valve stem and push the seal down until it touches the top of the valve guide.

At this point, the installation cap can be removed and placed on the next valve. A special installation tool can be used to finish pushing the seal over the guide until the seal is flush with the top of the guide.

Installing Umbrella-Type Valve Seals An umbrella-type seal is installed on the valve stem before the spring is installed. It’s pushed down on the valve stem until it touches the valve guide boss (Fig ure 12-80). It will be positioned correctly when the valve first opens.

Installing O-Rings:

When installing O-rings, use engine oil to lightly lubricate the O-ring. Then install it in the lower groove of the lock section of the valve stem (81). Make sure the O-ring is not twisted.

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Valve spring assembly Valve locks (keepers) Valve guide seal Valve guide Spring retainer Fgr__80 Valve assembly with an umbrella-type oil seal. Courtesy of Federal-Mogul Corporation Spring retainer O-ring Spring Keepers (valve locks) Fgr__81 Valve assembly with an O-ring valve seal. Federal-Mogul Corporation

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ASSEMBLING THE CYLINDER HEAD

Before a cylinder head is reassembled and installed, two critical measurements must be carefully checked: the installed stem height and the installed spring height.

Installed stem height is the distance between the spring seat and stem tip. A number of tools can be used to obtain an accurate stem height reading, including a depth micrometer, vernier caliper, and telescoping gauge.

USING SERVICE INFORMATION

Stem height specifications are often unavailable in service manuals. As a guide for assembly, record the stem heights for all valves during disassembly.

Another specification related to installed stem height is installed spring height. Installed spring height is measured from the spring seat to the under side of the retainer when it’s assembled with keepers and held in place. This measurement can be made by using a set of dividers or scales, telescoping gauge, or spring height gauge.

If the spec for installed spring height for an exhaust valve is 1.600 inches (40.64 mm), and the measurement is 1.677 inches (42.54 mm), the increase in height is 0.077 inch (1.95 mm). This means the installed stem height has also been increased by 0.077 inch (1.95 mm).

Adjustments to valve spring height can be made with valve spring inserts, otherwise known as spring shims. Even though valve shims come in only three standard thicknesses-0.060, 0.030, and 0.015 inch (1.52, .7620, and .3810 mm)-using combinations of different shims gives the correct amount of compensation (within 0.005 or 0.010 inch [0.1270 or 0.2540 mm]).

SHOP TALK -- Valve keepers should be replaced in pairs. If a new keeper is mated with a used one, the spring retainer may cock and break off the valve tip or allow the assembly to come apart.

By comparing spring height to specifications, the desired amount of spring tension correction can be easily determined. For example, if spring height is 0.180 inch (4.59 mm) and the specifications call for 0.149 inch (3.78 mm), a 0.030-inch shim (0.149 inch _ 0.030 inch _ 0.179 inch [3.78 mm _ 0.7620 mm _ 4.54 mm]) would be needed. If more than one shim is required, place the thickest one next to the spring. If one side of the shim is serrated or dimpled, place that side onto the spring seat.

The end of the spring that is wound the tightest should always be placed toward the head of the valve.

This is also true of mechanical surge and vibration dampers.

With the valve inserted into its guide, position the valve spring inserts, valve spring, and retainer over the valve stem. Using a valve spring compressor, com press the spring just enough to install the valve keepers into their grooves. Excess pressure may cause the retainer to damage the oil seal. Release the spring compressor and tap the valve stem with a rubber mallet to seat the keepers. When doing this, the valve will open slightly. To prevent damage to the valves, never tap on the stems with the cylinder head lying flat on the bench.

Turn the head on its side or raise it off the bench.

!CAUTION! If the keepers are not fully seated, the spring assembly could fly apart and cause personal injury (or serious damage to the engine if it occurs while the engine is running). For these reasons, it’s good practice to assemble the valves with the retainers facing a wall and to wear eye protection.

OHC Engines

After the valves are installed and the cylinder head is assembled, the camshaft can be installed in the cylinder head. Some engines have a separate camshaft housing that bolts to the cylinder head. This should be installed with the proper seals and gaskets. Make sure the seals are properly seated in their grooves before tightening the housing to the head.

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Next: part 7

Prev.: part 5