Cylinder block for horizontally opposed engine

Fig 4.4

The arrangement of the cylinders for a horizontally opposed engine is shown in Figure 4.4. This has a split crankcase. There are actually two cylinder blocks joined together by the flanges of the crankcase. The cylinder blocks are of aluminium alloy, with cylinder liners of cast iron cast into the aluminium block during manufacture.
As with all cylinder blocks, the aluminium alloy castings are made with ribs, webs and fillets to provide rigidity.

Two-part cylinder block
The cylinder block for the four-cylinder in-line engine shown in Figure 4.5( as you have seen in last post "Cylinder blocks,  assembly and construction) is made in two parts — the cylinder block and the base plate. Both parts are made from aluminium. The cylinders have dry liners that are pressed into the block and these are not replaceable.
The main bearing caps are combined with the base plate which has webs that carry the lower halves of the crankshaft main bearings. The cylinder block and the base plate are matched during manufacture and cannot be replaced separately.

·       With this design, there are no individual caps for the main bearings.

The methods used to make aluminium castings enable detailed components to be produced. For example, in the cylinder block shown, the oil filter housing is cast as part of the cylinder block and the base plate has the mounting for the starter.
In addition to the two parts of the cylinder block, there is a cast aluminium oil pan bolted to the underside of the base plate. This further increases the rigidity of the assembly.

Fig 4.6

Cylinder sleeves
Cylinder blocks can be designed with cylinder sleeves (or liners). These are fitted to cast iron blocks and are different to the liners that are cast into aluminium alloy cylinder blocks.
With cast iron blocks, the sleeves are cast separately and then fitted into place in the block when the engine is being assembled. Separate sleeves allow more control over the manufacturing process and a grade of iron that is different from the block can be used. The cast iron for the block can be of a grade which is easy to cast, while the sleeve is made more resistant to wear.
There are three types of cylinder sleeves: dry sleeves, flanged dry sleeves, and wet sleeves (Figure 4.6).

Dry sleeves
A thin dry sleeve is of uniform diameter throughout its length and is a press fit in its bore in the cylinder block. The wall of the sleeve is about 2 mm thick, and its outer surface is in contact with the block for its full length. The top of the sleeve is finished flush with the top of the cylinder block and is hardly visible.
This type of sleeve is sometimes fitted to new engines, but is used to recondition badly worn or damaged cylinders that cannot be re-bored without removing excess metal.

·       These dry sleeves form a permanent part of the cylinder block and normally cannot be

removed.

Flanged dry sleeves

Flanged dry sleeves are sometimes used on larger engines. These are similar to a normal dry sleeve, except that they have a flange at the top which fits into a recess in the surface of the cylinder block. The sleeve is not a tight fit, and it can be removed when worn and a new sleeve fitted in its place. The cylinder head holds the flange down and prevents the sleeve from moving.
The bore in the block must be true because the accuracy of the sleeve depends on its contact with the block. This also has a bearing on heat transfer from the cylinder.
This type of sleeve is not generally used for passenger or light commercial vehicles.

Fig 4.7

Wet sleeves
The outer surface of a wet sleeve forms part of the water-jacket around the cylinder. It is called a wet sleeve because it has coolant against its outer surface. This eliminates problems of heat transfer between the sleeve and the coolant in the water-jackets. However, the sleeve must be sealed to prevent coolant leaks. Seals are used at the top to prevent coolant from entering the combustion chamber and at the bottom to prevent coolant from entering the crankcase.
Figure 4.7 shows a cylinder block and wet sleeve. The block does not have full-length bores, but has mounting holes at the top and bottom. Wet sleeves have thicker walls than dry sleeves. They do not have the same support in the block and they depend on their wall thickness to prevent distortion.

The top of the sleeve has a flange which fits into a recess in the block. Some sleeves have a sealing ring under the flange as well as the cylinder-head gasket. The lower end has one or two neoprene sealing rings.
Engines with wet sleeves can be reconditioned by fitting new sleeves and pistons which are supplied ready to install.

Continued

See cylinder surface-finish>>>>>>>>>>>

Cylinder blocks, assembly and construction

The cylinder block is the largest part of the engine and is the base to which many other parts are assembled or attached. The upper part of the block carries the cylinders and pistons, and the lower part forms the crankcase which supports the crankshaft. The cylinder block has to be rigid to withstand the stresses and vibration to which it is subjected, and must be unaffected by temperatures reached when the engine is in operation.
Balance is an important part of engine design and so this has also been included in this blog.

Cylinder blocks

Fig 4.1

Cylinder blocks are made of cast iron or of aluminium alloy. Aluminium cylinder blocks are cast from aluminium alloyed with other materials. Cast iron cylinder blocks are usually cast from grey iron alloyed with other metals such as nickel or chromium.
During manufacture, patterns that are the shape of the cylinder block are used to form a sand mould. Molten cast iron is then poured into the mould where it cools to become a rough casting of a cylinder block.
Before casting, the shapes of water-jackets, cylinders and some other parts are made up as sand cores. The cores are fitted into the moulds so that these parts of the block do not become solid cast iron during the casting process.
After casting, the core sand is removed through holes in the sides and ends of the block provided for this purpose. This leaves internal spaces for the water-

jackets and other parts. The holes are later fitted with steel plugs which are referred to as expansion plugs, core plugs, or welsh plugs. They can be seen in the cylinder block in Figure 4.1. When installed, they are held in place by sealer and expansion of the plug against the hole.

·       The plugs in the side of the block are cup-shaped and the one in the rear end of the block

    is convex.

During manufacture, the casting undergoes a number of machining operations which include boring and finishing the cylinders, machining surfaces, drilling holes and cutting threads to produce the finished cylinder block.

Cylinder-block assembly

Fig 4.2

The components of a basic cylinder-block assembly are shown in Figure 4.2. These are some of the main parts of the engine. An assembled cylinder block (with the crankshaft, connecting rods and pistons) is sometimes referred to as a short motor. A short motor does not include the cylinder head, the oil pan, the timing pulleys, timing belt or the flywheel.
The lower section of the engine block forms the crankcase, and the part of the crankcase that extends below the main bearings is called the skirt. In some engines, the skirt is extended well below the centreline of the crankshaft and is called a full skirt. This is done to give the engine rigidity. Other engines have a very short skirt or none at all and rigidity is obtained in other ways.

Cylinder-block construction

In most engines, the cylinders, cylinder block and crankcase are all cast together. This is known as mono-block construction, as distinct from engines that have their cylinders as separate parts. This is the case with air-cooled engines where the cylinders are made separately to the crankcase.
Mono-block engines with cast-iron blocks have the cylinders bored directly in the cast iron casting. Cast iron is a suitable material for cylinders because it wears well and resists the effects of heat. Cylinder walls can be plated with chromium, which is very resistant to wear, although this is not common for passenger car engines.

Aluminium cylinder-blocks

Fig 4.3

Some cylinder blocks are cast in aluminium alloy. This has the advantage of being lighter than cast iron. Aluminium alloy on its own is not suitable for cylinders. It is a soft material that wears rapidly under the action of the pistons and piston rings. For this reason, liners of a harder material are often used in the cylinders.
The liners are cast iron sleeves that are either cast or pressed into the block. Liners that are cast into the block have grooves on the outside that form a key between the liner and the block. This prevents any possible movement and the sleeve becomes a permanent part of the block. (The cylinder blocks in

Figure 4.5 arc of cast aluminium alloy with cast iron liners.)

• The terms cylinder liner and cylinder sleeve are generally interchangeable.

Aluminium cylinder block without liners

Aluminium cylinder blocks can be designed without liners, but special alloys are needed. Figure 4.3 shows a V-8 cylinder block that has no cylinder liners. The aluminium alloy of the cylinders has been specially treated to expose hard silicon crystals. This provides a low-wearing surface for the pistons and piston rings.
Aluminium alloy is used in the cylinder block to reduce the weight of the engine, but there is also an advantage that it is better at transferring heat than cast iron. The aluminium of the block has a similar expansion rate to the pistons.

Fig 4.5

 Continued

See two-part cylinder block>>>>>

Camshaft service

Fig. 3.43 (a)

The procedure for camshaft removal varies considerably with different engines. In OHV engines, the camshaft is mounted in the crankcase and is accessible from the front of the engine after removing the timing cover and timing chain.
The rocker arm assembly and push-rods also have to be removed, and the valve lifters must be removed or raised to clear the cams before the camshaft can be withdrawn through the front of the engine.
With OHC engines, the camshaft is more readily accessible on top of the cylinder head. Before the camshaft can be removed, the timing pulley or sprocket and the timing belt or chain is removed from the front of the camshaft. There is also a valve-operating mechanism that might have to be removed from the cylinder head.
The camshaft bearing caps have to be removed before the camshaft can be lifted from the lower half of its bearings. The bearing cap bolts should be released progressively and in a recommended sequence.

Fig. 3.43 (b)

Checking a camshaft
A camshaft can be checked for alignment by mounting it in V-blocks and using a dial gauge to cheek for eccentricity. Journal diameters should be checked with a micrometer, and the bearings with a telescopic gauge. The two dimensions can then be compared to determine whether bearings are worn (Figure 3.43).
With the camshaft removed, cam wear can be checked visually and also by measurement with a micrometer.
Figure 3.44 shows normal and abnormal wear patterns. If wear shows across the full width of the cam, and excessive wear of the cam lobe has taken place, a new camshaft should be installed. The valve lifter or other mechanism should also be checked.

Fig. 3.44

Checking cam Lift

Camshafts can also be checked while installed in the engine. Figure 3.45 shows how this is done on an OHV engine.
With the rocker assembly removed and the dial gauge positioned as shown, the crankshaft is turned slowly until the valve lifter is on the base of its cam. The dial gauge is set to zero and then the crankshaft is rotated until the lifter is on the top of the lobe. The reading is the cam lift. This can be compared with the other cams and with the engine’s specifications.
On OHC engines, the dial gauge can be mounted on the cylinder head so that its plunger is in direct contact with the cam, although rocker arms will have to be removed on some engines.

Camshaft bearings
Camshaft bearings of OHV engines can be removed from the engine block with a special bearing remover, but this is a fairly major operation.
The remover is a threaded puller bar that is inserted through the bearings. Puller sleeves that are slightly smaller than the bearing outside diameter arc installed on the bar behind the bearings. When the nut on the end of the puller bar is turned, the bearings are pulled from their bores in the crankcase. New bearings are installed with a similar method.
Camshaft bearings of OHC engines can be checked for clearance with plastigage, but they are not usually replaceable.

Timing gears, chains and sprockets
Gear and sprocket run out can be checked by mounting a dial gauge on the cylinder block or head, with the plunger resting on the side of the gear or sprocket.
Backlash between gears is measured by a dial gauge, or by inserting narrow feeler gauges between the meshing teeth. Excessive run out or backlash will require replacement of one or more gears.
Timing chains can be checked for tension and wear. Excessive slack, which cannot be corrected by adjustment, indicates a worn chain and possibly worn sprockets. Worn parts should be renewed.

Fig 3.46

Timing belt and pulleys
Timing belts should be checked for tension and adjustment. They should also be checked for condition as shown in Figure 3.46. If a timing belt is being removed and is to be reused, then an arrow should be chalked on the back of the belt. This is to show the direction in which it runs. When reinstalled, the belt must run in the same direction.

Continued

See Cylinder blocks, assembly and construction 

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.

Fig 3.40

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.

Fig 3.41

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.

Fig 3.42

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.

Continued

See camshaft service>>>>>>>>>>>>>>>>

Synchro-seating valves

Fig 3.31

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.

Fig 3.32 (a & b)

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.

Fig 3.33

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.

Fig 3.34

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.

Fig 3.35

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.

Fig 3.36

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.

Fig 3.37

·           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.

Fig 3.38

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.

Fig 3.39

Continued

See servicing valve-seats inserts>>>>>>> 

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.

Fig 3.27

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.

Fig 3.28

Fig 3.29

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.

Fig 3.30

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.

Continued

See Synchro Seating valves

Testing hydraulic valve lifters

Fig 3.25

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 a immersed for bleeding.

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

Valve refacers and refacing

Fig 3.26 (a)

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

Fig 3.26 (b)

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 its 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.

Fig 3.26 (c)

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.

Fig 3.26 (d)

Continued

See valve-seat reconditioning>>>>>>>>>