Servicing valve-seat inserts

Servicing valve-seat inserts

A valve-seat insert would only be replaced if it had reached a stage where it was pitted or burnt and its seat could not be reconditioned. It would then be necessary to remove the insert from the cylinder head and replace it with a new one.
Inserts are an interference fit in the cylinder head, so are not easy to remove. They can be removed by being cut out with inserting equipment, or they can be shrunk to make them easier to remove. This is done by running a bead of weld around the inside of the insert, which shrinks as it cools. This loosens the insert in the head.

• There are precautions to be taken during welding so that the cylinder head is not heated and distorted.

The objectives, when fitting a valve-seat insert in a cylinder head, are:

1. To cut a recess in the valve port that is concentric with the valve guide.
2. To fit an insert that will bring the valve seat back to standard and remain securely in position.

Cutting a recess

A valve-seat recess cutter is shown in Figure 3.40. It consists basically of an anchor that is mounted on the cylinder head and a spindle with a handle. A cutter is fitted to the bottom end of the spindle. The tool is adjustable so that the cutter can be positioned accurately over the valve port.
Hand-operated equipment is shown, but machine- operated equipment is used in reconditioning workshops.
To cut a recess for an insert, a cutter to suit the diameter of the insert is selected. The cutter is fitted to the spindle and a stop on the tool is adjusted for the depth of cut. The spindle is turned by the handle to rotate the cutter and, at the same time, the feed nut is turned. The feed nut applies a light load to the cutter and keeps it cutting.
When the feed nut reaches the stop that was previously set, the cutter will no longer cut and the recess will be at the correct depth.

Selecting an insert

The insert is selected for type of material and size of the valve port. Alloy inserts are usually fitted to both the intake-valve and exhaust-valve ports.

The size of the insert is found by measuring the original insert, or from the insert-maker’s data chart. Three dimensions are needed: outside diameter, inside diameter, and depth, as shown in Figure 3.41.
When the correct cutter is used, the recess will be slightly smaller in diameter than that of the new insert to be fitted. This will provide an interference fit of approximately 0.15 mm to 0.25 mm. 

Fitting an insert

A punch is used as shown in Figure 3.42. The insert is driven firmly on to its seat. No lubrication is used.

After the insert is installed, the final operation is to cut and finish the valve seat to the correct angle. This is the same as for a normal valve-seating operation.
With aluminium cylinder heads, the valve-seat inserts are removed from and fitted to a cylinder head when it has been heated. Heating is done as indicated previously for fitting valve guides (see Figure 3.38). The inserts can also be chilled in dry ice before being fitted. With a heated head and chilled insert, very little punching is needed.

Synchro-seating valves

Synchro-seating valves
A process known as synchro-seating can be used to produce valve seats with a fine finish and at exactly the same angle as the valve faces.
With this method, the valves are refaced in the usual way, and the seats in the cylinder head are rough-finished to the correct angle with a stone.
After rough-finishing the seats, the carrier with its stone and pilot is mounted in the valve refacer in the same way as a valve (Figure 3.31). The grinding wheel is then used with a very light feed to dress the stone, just as if grinding a valve. The stone will have a fine finish at exactly the same angle as the valves.
The seats are then given a finish grind with the finely dressed stone. With this method, the seat angle will match that of the valves. The valves can be checked for correct sealing with bearing blue, but lapping is normally not required.

Valve-seat cutters
Figure 3.32 shows valve-seat cutters that are used to restore valve seats. These have a number of tungsten steel cutting blades. They can be used with a T-handle, or they can be power-driven. Figure 3.32(a) is a seat cutter with blades at 30° and 45°. Figure 3.32(b) is a narrowing cutter with its blades at angles for top- narrowing and bottom-narrowing of seats.

The cutting head is fitted with two sets of blades, so either side of the cutting head can be used. The blades are mounted in slots in the cutting heads and retained by screws. They can be adjusted by altering their position in the slots and they are replaceable.

Using the cutting equipment
A cutter of the correct size for the valve seat is selected and the blades adjusted to suit the seat diameter. The cutter is fitted to a carrier with a handle. A pilot of the same diameter as the valve stem is installed in the valve guide and the carrier with its cutter is installed on the pilot. To make a cut, the cutter is turned clockwise while
maintaining a light downward pressure. A finish cut of one or two turns is made without pressure.

Cutting a seat
The procedure for cutting a valve seat is shown in Figure. 3.33, is as follows:

1. Clean the seat with one or two turns of a seat cutter. Visually inspect the seat for pits and bums that will have a bearing on the amount of metal to be removed.

2. Take a bottom cut with a narrowing cutter — this operation raises the seat.
3. Take a top cut with a narrowing cutter until the seat width is slightly narrower than required — this operation lowers the seat.
4. Finish cut with the seat cutter, cutting lightly until the seat is the correct width.

Valve-seat reamer
A valve-seat cutter of the type also referred to as a reamer is shown in Figure 3.34. The cutter has a number of cutting teeth machined at an angle, and a tapered hole in the centre, which enables it to be fitted to a pilot.

The pilot is installed in the valve guide and the cutter is rotated by means of a T-handle. A downward pressure is applied so that the teeth will cut the valve seat. This type of cutter is usually used for relatively soft seats.

Servicing valve guides
Valve guides can be checked for wear in a general way by using a new valve as a gauge. The valve stem should be a free-sliding fit in the guide without excessive free play. The stem-to-guide clearance is about 0.05 mm to 0.1 mm, with the exhaust valve usually having a slightly greater clearance than the intake valve.
To measure guide wear, the valve is held slightly clear of its seat by a spacing sleeve. A dial gauge is mounted on the cylinder head, with its plunger against the head of the valve (Figure 3.35). The valve can then be moved from side to side of the guide, to indicate the clearance on the dial gauge.

An alternative method is to mount the dial gauge against the end of the valve stem, with the valve resting lightly on its seat.

• In the methods described, the dial gauge indicates wear, but does not accurately measure the clearance.
  

Valve guides wear eccentric, and also bell-mouth. A telescopic gauge and micrometer can be used to detect these types of wear. Bell-mouth is wear at the end of a hole that causes it to become somewhat bell-shaped.

Replacing valve guides
Most valve guides are replaceable, but valve guides can also be cast integral with the cylinder head. Methods of service differ with each type.
With replaceable guides, the old guides are either pressed or driven out of the cylinder head (Figure 3.36). This is often done from the spring end of the guide because the valve-port end can become brittle and coated with carbon, making the guide hard to remove.
New guides should have an interference fit in the cylinder head of about 0.1 mm. They are driven or pressed into the head with a stepped punch. When installed, they should project from the top of the head the same distance as the original guides.
When fitting new guides, a guide can be installed in the correct position at each end of the cylinder head. A straightedge is then used between these two guides as a height gauge for the other guides. After fitting, a guide may have to be lightly reamed to provide a fit for the valve stem (Figure 3.37).
Integral valve guides are part of a cast iron cylinder head and cannot be removed. However, worn guides of this type can be reamed oversize and new valves with oversize stems fitted.

• Cast iron cylinder heads can be worked on cold, but aluminium cylinder heads must be heated.

Valve guides in aluminium heads.
Valve guides are removed from an aluminium cylinder head after it has been heated. Heating can be done in an oven, or in water as shown in Figure 3.38. The head is heated to about 90°C. The guides can be removed once the cylinder head has reached a uniform temperature.
New valve guides must have the correct interference fit in their bores in the cylinder head. Before the new guides are fitted, the cylinder head must be reheated. A stepped punch or press tool is used to replace the guides.

Restoring valve guides
Valve guides can he restored by knurling. With this process, valves with oversize stems are not required. In the knurling process, a special tool with a small knurling wheel is used to form a spiral groove down the inside of the valve guide. The tool displaces metal on each side of the wheel as it works its way down the guide and this reduces the guide’s diameter.
After knurling, a reamer is used to ream the guide to fit the valve stern. When restored, the valve guide will have a spiral groove from top to bottom and the valve stem will have minimum clearance in its guide.
A valve and reworked guide are shown in Figure 3.39.

Continued

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Valve-seat reconditioning

Valve-seat reconditioning

Worn or burnt valve seats in the cylinder head can be restored by either grinding or cutting. This removes pit marks and bums and produces a seat that is concentric with the valve guide. The seats can also be narrowed to give them the correct width.

Valve-seat grinding
With this method, small grinding stones are used to restore the valve seats. The stones are available in various diameters and are dressed to suit the valve-seat angle. Narrowing stones are dressed to other angles. The stones are mounted on the threaded end of the
stone carrier (Figure 3.27). To grind the valve seat, the carrier is mounted with a pilot in the valve guide and driven by an electric drill.
The carrier has a clutch as part of its drive. The clutch is designed to have some slip and this can be adjusted by the knurled sleeve at the top of the carrier. Clutch slip causes the stone to chatter on the seat that is being ground and this assists the grinding action. The clutch can be adjusted for roughing or finishing.

Pilots
There are two types of pilots on which the carrier is mounted: expanding pilots and solid pilots. They are used in the valve guide to support the stone carrier as it rotates. This keeps the stone grinding the seat true with the valve guide.
An expanding pilot is held stationary in the valve guide and the carrier spins on it. A solid pilot is fitted to the stone carrier and rotates in the valve guide.
The valve guides must be clean and not excessively worn, and the pilot must be correctly fitted. Any errors or looseness will cause the seat to be ground eccentric with the guide so that the valve will not be able to seat properly.

Stone dresser
A jig is used to dress the grinding stones to the correct angle. The carrier, with the stone attached, is spun on a pilot on the jig by the drill. A small diamond in the end of a holder is moved across the stone at the desired angle. This dresses the stone. A light pass will produce a fine finish on the stone and a heavier pass will produce a coarse finish.

Grinding valve seats

The procedure for grinding a valve seat is as follows:
1. Clean the valve guides thoroughly so that the pilot will centre correctly in the guide. This ensures that the valve seat is ground concentric with its guide.
2. Select a stone to suit the diameter and the angle of the valve seat. Fit it to the carrier and dress if necessary.
3. Select a pilot to suit the valve guide. Fit this to the carrier or into the valve guide. (This will depend on the type of equipment.)
4. Place the carrier on the pilot and spin it with the electric drill, applying a light pressure to grind the valve seat. The clutch in the carrier can be adjusted to produce chatter, which assists with grinding.
5. Make a light grind to check that the stone is grinding correctly, then continue to clean up the seat.

•  Care must he taken to ensure that the valve seat is ground concentric with the valve guide.

Lapping valves
After the valves have been refaced and seats ground, then the valve and seat can be lapped to each other as follows:
I. Place a small amount of fine valve-grinding paste evenly around the face of the valve, keeping it away from the valve stern.
2. Place the valve in its guide and, by means of a suction cup and handle, rotate the valve back and forth a few degrees on its seat, using a light pressure (Figure 3.28).
3. Raise the valve frequently during lapping and turn it to a new position after a few laps.
4. Lap only until a continuous but narrow lapping mark is obtained on both the seat and face.
5. To check for correct seating, the valve face can be given a light coating of bearing blue, installed in its guide and turned against its seat (Figure 3.29).

• After lapping, all traces of grinding paste must he cleaned from both the seat and the valve.

Narrowing valve seats

The width of a valve seat is important. A narrow seat is desirable to give a good seal, while a wider seat is needed to transfer heat from the valve head to the cylinder head. A compromise is therefore necessary, with the intake valve seat usually being narrower than the exhaust valve seat.
Specifications vary for different engines but examples of valve-seat widths are:

Intake valve 1.5 to 2 mm
Exhaust valve 1.8 to 2.5 mm.

If a seat is too wide, it can be narrowed by grinding the top and/or bottom of the seat to reduce its width (Figure 3.30).
The position of the valve on the seat can also be altered. Narrowing by removing metal from the top of the seat will lower the seat in relation to the valve face. Narrowing by removing metal from the bottom of the seat will raise the seat in relation to the valve face.

• During reconditioning, it is often necessary to grind angles at the top and bottom of the seat to obtain the correct seat.

Testing Hydraulic Valve Lifters

Testing hydraulic lifters

Hydraulic valve-lifters are tested for their leak down rate.  A good lifter will leak down slowly but, if it’s plunger is sticking, the leak down rate will be too slow.  Its plunger is worn, or the check valve is leaking, then the leak-down rate will be too fast. The tester (figure 3.25) consists of a base with vertical standard carrying a ram. It has a cup with test fluid. The ram is operated by the weight on the end of an arm. A scale and pointer indicate movement of the plunger. A watch is used for timing.

1.     Place the lifter in the tester cup and cover with fluid.  Either a special light oil or distillate is used.

2.     Place the steel ball in the push-rod cup under the end of arm.

3.     Work the plunger up and down with the weight until the air is bled from the lifter and it is full of fluid.

4.     Adjust the length of arm so that point there is in line with the top mark of the scale when the ram is just touching the ball in the push-rod cup.

5.     Raise the lever and let the weight and ram force the plunger down.

6.     Measured the time that the pointer takes to move across the scale.  This is the leak-down rate.

As an example, a used lifter must take at least 5 seconds, but not more than 60 seconds to leak-down and a new lifter should take at least 10 seconds but not more than 60 seconds. A Doubtful lifter should be tested three or four times. If a lifter does not test within specifications it should be discarded and replaced with a new one.

Hydraulic lash adjusters

Some hydraulic lash adjusters for OHC engines can be tested in a similar manner to that described for hydraulic valve lifters. Generally, hydraulic lash adjusters can not be dismantled, but they can be bled to remove air. This also provides limited cleaning.

A faulty lash adjuster will produce noise with the engine idling at normal operating temperature.  Some noise is not unusual when the engine is cold and has been standing, because the plunger of that adjuster could have leaked down.

Hydraulic lash adjusters can be bled of air by working them in a container of distillate.  Clean distillate must be used. To prevent contamination, the outside of the adjuster should be cleaned before it is an immersed for bleeding.

• If a lash adjuster is still noisy after bleeding, it will have to be renewed.

Valve refacers and refacing

Valve refacers consists basically of two grinding wheels and a work ahead which holds and rotates the valve (figure 3.26). Valve refacers are used to restore valves by producing a final ground valve face. This must be at the correct angle and concentric the valve-stem.

Grinding wheel

The main grinding wheel is mounted on a spindle and driven at high-speed by an electric motor.  The wheel must be well-balanced to prevent vibration that would cause chatter marks when grinding the valve face.

The face of the grinding wheel is dressed occasionally to keep it flat.  A dressing tool that contains small industrial diamond is used.  The wheel is given only a light dressing as this will produce a fine surface on the face of grinding wheel.  Dressed correctly, grinding wheel will produce a smoothly ground valve face.

Workhead

The workhead is shown in figure 3.26 (b).  This holds the valve by gripping it in a collet. The valve must be correctly centered in the workhead.  Any error will be producing a valve with the face eccentric to the stem.

The workhead has a degree scale on its base so that the valve-face can be set and the correct angle to the grinding wheel.  When the machine is being used, the valve rotates slowly against the face of the grinding wheel.

Controls

There are two hand operating controls:

1.        A hand wheel that operates a feed screw to move the grinding wheel forwards and backwards.

2.        A hand lever that moves the face of the valve across the face of the grinding wheel.

The valve is ground by using the hand wheel to bring the grinding wheel up against the valve-face and then using the lever to move the valve slowly across the face of the grinding wheel.

To produce a fine finish, a light feed is used And the valve is moved backwards and forwards across the face of the wheel. For best results, valve is kept against the face of the wheel during grinding and not to run off it’s of the wheel.

A small pump supplies coolant from a tank in the base of the machine coolant is directed to the face of the wheel where it keeps the valve cool and helps to produce a fine finish.

• The valve is ground just enough to produce a smooth face. If the margin becomes too thin, the valve should be scrapped.

Valve tip grinder

A cupped grinding wheel is fitted at the tail end of the machine.  This is used with an attachment as shown in figure 3.26 (c) to grind to grind the tip of the stem flat.  The valve is clamped in a v-support and micrometer fitting is used to adjust tip of the valve against the grinding wheel.  The attachment with valve is swung backwards and forwards across the grinding wheel. The micrometer fitting enables the amount of metal being removed to be measured.

Rocker arm grinder

An attachment can be used to grind the worn ends of rocker arms as shown in figure 3.26 (d).  The rocker arm is mounted on an attachment that moves its end across the cupped grinding wheel. An adjustment enables the rocker arm to be set so that it will be ground to the right shape. This is referred to as radius grinding of the rocker arm.

Continued

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Servicing valves and springs

The parts to be checked on a valve are shown in figure 3.19.  The valve face should be inspected for wear, pits, grooves and burn marks to determine if it is suitable for further use.  Minor defects, such as pits and groves, can be removed by re-facing the valve, but a valve that is badly burnt, warped or cracked should be discarded.

The margin or thickness of the edge of the valve face should be about 1 mm minimum.  A margin that is to thin will cause the valve head to overheat and the edge will burn.

The Valve-stem should be inspected for a bent condition and the end of the stem inspected for groves or scores.  The clearance of the stem in the valve guide must also be checked.

Testing valve springs

Valves springs should be tested for compression and for squareness.  Special testers are used.  These measure the force required to compress the spring to the specified length (figure 3.20).

To check for squareness, stand the spring on end on a flat surface against a square (figure 3.21).  The spring should be rotated slowly to see if the top coil moves away from the blade of the square. Turn the spring Upside down and check again. If the spring is more than 2 mm out of square, or if it does not have correct compression at the specified length, then it should be discarded.

Weak springs that do not close the valve quickly enough will allow gas leaks and cause excessive valve head temperatures.  They could also cause excessive wear to the lifters or cams.

• Springs that are not square impart a sideways thrust to the valve-stem, causing excessive wear to the stems and guides.

Replacing valve-seals or springs

On some engines, the Valve-stems seals and springs can be removed and installed without removing the cylinder heads from the engine.

An adapter is fitted to the spark-plug hole and an air line connected.  Compressed air is then applied to the cylinder to hold the valve against its seat, and the special tool is used to depress the valve-spring (figure 3.22).  The method can be used with different types of valve- mechanisms, providing a suitable tool is available and the top of the valve-spring is accessible. With some OHC engines, camshaft would have to be removed.

To remove the valve-spring, the piston of the particular cylinder is brought to TDC on the compression stroke and air pressure is applied to the adapter and the spark-plug hole. The engine should be prevented from turning so that valve will rest on top of the system should air pressure be lost.

• If air pressure will not hold the valve on its seat, then a faulty valve or seat is indicated.

Servicing rocker arm assemblies

Where the rocker arms are mounted on a shaft, the rocker arms are moved as an assembly and then removed from the shaft. The arrangement of arms, springs and washers should be carefully checked and laid out in order.  All rocker arms are not the same shape.

On engines with independently mounted rocker arms are dismantled separated by removing the mounting stud that is threaded into the Cylinder-head.

After the rocker arms are removed, they should be examined for the wear or damage. Rocker arms with bushings can be re-bushed if they are worn. On some rocker arms, and that operates against the cam has a roller. Other rocker arms can be ground on the valve re-facer, but excessively worn rocker arms have to be replaced.

Servicing hydraulic lifters and lash adjusters

The valve train length can be checked on OHV engines that have been hydraulic valve-lifters.  The purpose of this is to see that the hydraulic lifter is able to operate properly.  With a good lifter, the plunger of the hydraulic lifter normally operates around the center position of the body.

Check is made as follows:

1.     The crankshaft is turned so that the lifter is on the low part of that cam.

2.     Special tool is used on the rocker arm to force the oil from the lifter so that the plunger bottoms in the body (figure 3.23).

3.     Feeler gauges are then used to check the clearance between that tip of the valve-stem and the rocker arm.

4.     If clearance is too small, the valve might not close properly.  If the clearance is too large, then the lifter could be noisy in operation.

If the valve-train has no adjustment and if the valve is noisy, the hydraulic valve-lifter will have to be dismantled and cleaned, or replaced.

Lifter problems

The most common problems with the valve-lifters are caused by dirt, gum, and varnish and air bubbles in the oil. Dirt and gum can cause the plunger to stick, or prevent the check valve from functioning.  The lifter will have to be removed from the engine, dismantled and cleaned.

Air in the lifter will compress and prevent the lifter from operating properly, but this can usually be corrected by bleeding.

Dismantling hydraulic lifters

A dismantled hydraulic lifter is shown in figure 3.24.  To dismantle, push-rod cup and plunger are depressed and the circlip removed.  This allows the push-rod cup, the plunger and the valve to be removed from the body of the lifter.

Observe the sequence of dismantling, as the assembly must be done in the reverse order.  Work on one lifter at a time.  The parts are not interchangeable and must not be mixed with other lifters.

Check the condition of the parts, including the roller, or if there is no roller, check the bottom of the lifter for wear.

If the parts are serviceable, then the parts can be cleaned distillate, reassembled and the lifter tested.

• If the parts are scored or defective in any way, then the complete lifter should be renewed.

Continued

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