Cylinder head refurbishment (Mitsubishi Galant 6)

General information

Modern automobile engines use one of two types of cylinder heads: overhead valve (OHV) and overhead camshaft (OHC). The latter type can be divided into sensor-switch subgroups: with one overhead camshaft (SOHC, or simply OHC) and with two overhead camshafts (DOHC).

Currently, cylinder heads are manufactured using casting from aluminum alloy, which allows for a significant reduction in the overall power unit while maintaining such vital properties as reliability and heat dissipation ability.

In fairness, it should be noted that, along with aluminum, traditional cast iron is also quite widely used in the manufacture of cylinder heads. Regardless of the material, all heads are equipped with valve seats. In some heads, there are two valves per cylinder, although recently the multi-valve configuration has become increasingly widespread, where each cylinder can be equipped with three, four, or even five valves. Fine mechanical lapping of the working chamfers of the plates to the seats ensures the tightness of the combustion chambers in the closed position of the valves. The use of guide bushings ensures the unambiguous reciprocating movement of the valves and the centering of the latter relative to the seats. In view of the above, the size of the clearance of the valve stem in the guide bushing becomes critical. Excessive clearances usually increase engine oil consumption, vacuum losses may occur, and the likelihood of damage to the valve seats increases. If the valves are too tightly fitted in the guide bushings, they may jam, which inevitably reduces the power developed by the power unit and increases the risk of engine seizure. In addition to the guide bushings, the valves are also equipped with springs that ensure the necessary pressure of the plates against the seats and return them to the closed position after forced opening under the force developed by the eccentric cams of the camshaft(s). Special plates and two-section split locks (crackers) are used to fix the springs on the valve stems. In heads made of aluminum alloy, special adjusting washers are installed on the valve springs to protect the latter from wear.



Ideally, during a major (restorative) repair of the cylinder head, all valves should be replaced together with springs and guide bushings. However, depending on the condition of the serviced engine, which is determined mainly by the conscientiousness of the car owner, there may be no need for such replacement. The main reason for premature wear of valve train components is incorrect adjustment of engine settings. Thus, prolonged operation of the unit on an over-enriched air-fuel mixture often leads to oil being washed out of the guide bushings by gasoline. Over-leanness of the mixture leads to an excessive increase in its combustion temperature, which leads to burnout of the valve plates and their seats. The service life of valve springs is directly related to the driving style inherent in the vehicle driver - frequent excess of engine speed inevitably leads to a faster failure of the springs.

Unfortunately, it is not possible to completely prevent wear of the internal components of the cylinder head. However, timely restoration repairs with careful grinding of the valves will allow the vehicle owner to reduce material costs by extending the service life of the cylinder head.

It should be noted that if only individual valves burn out, it would be reasonable to replace the entire set. This statement also applies to other components of the valve mechanism.

As unpleasant as it may be, it is only possible to determine the condition of the internal components of the cylinder head after preliminary disassembly. A description of the procedure for disassembling the cylinder head on the Mitsubishi models discussed in this Manual is given below in this Section.

Cleaning

1. A thorough cleaning of the cylinder head and valve train components followed by a detailed inspection of their condition will help determine the approximate scope of the upcoming restoration work.

Note: Severe engine overheating may result in deformation of the cylinder head and disruption of the flatness of its mating surfaces.

2. Scrape off all traces of the old gasket material and sealant from the mating surfaces of the cylinder head, intake manifold and exhaust manifold - try not to damage the surfaces. The work will be significantly facilitated by using a special softener, which should be pre-soaked in the adhering deposits - ask in car accessory stores.

3. Remove all traces of scale from the walls of the water channels.

4. Using a stiff wire brush, thoroughly clean all accessible cavities and openings. If the channels are heavily contaminated, head cleaning should be entrusted to specialists.

5. "Run" each of the bolt holes with a tap of the appropriate size, removing corrosion products and traces of old sealant from the threads and restoring damaged threads. If you have access to a source of compressed air, blow out the holes, removing chips and small debris from them.

When using compressed air, remember to wear safety glasses!

6. Use a wire brush to clean the threads of the intake manifold and exhaust manifold mounting studs.

7. Wash the head with solvent and dry it thoroughly. Using compressed air will significantly reduce the drying time and will guarantee the quality of cleaning of hard-to-reach cavities and holes.

Note: Various types of carbon deposit removers, which make the cleaning process much easier, can be purchased at many car accessory stores. Remember that these types of products are usually chemically aggressive and should be used with appropriate precautions - strictly follow the manufacturer's instructions, usually on the container label.

8. Wash the valve lifters with solvent, then dry them thoroughly. Using compressed air will make the procedure much easier (don't forget to wear safety glasses).

Note: Tappets equipped with hydraulic correctors should be placed upside down in an oil bath. Remember that during assembly all components must be installed strictly in their original places.

9. Wash in solvent and thoroughly dry the valve springs, their plates, seats and split lock crackers - try not to mix up the components.

10. Scrape off the bulk of the deposits that have formed on the valve surfaces, then use a wire attachment on an electric drill to finally clean the surfaces of the valve stems and plates - make sure that the valves are not mixed up.

Disassembly

The design of the cylinder head used on a specific engine (SOHC or DOHC) does not have a fundamental significance for the order of dismantling the components of the valve drive mechanism. Examples of the appearance of cylinder heads are shown in the illustrations. It should only be noted that when disassembling a DOHC head, special attention should be paid to the thoroughness of marking all components to be removed - the components of the intake valve drive should not be confused with the components of the exhaust valves during assembly if the cylinder number matches and they are almost completely identical in appearance. As a mnemonic rule when marking parts, remember that the intake camshaft with associated components is located on the side of the intake manifold, the exhaust - on the side of the exhaust manifold.

Cup-type tappet heads

1. Most cylinder heads use cup-type tappets in the valve train. In this design, the split lock crackers of the valve spring are housed inside the tappet seat. To disassemble this type of head, you will need a C-clamp valve spring compressor, a mandrel to remove the valve springs, and a small magnet to remove the split lock crackers.



2. If you have not already done so, remove the camshaft(s) and/or valve lifters from the cylinder head.

Note: Place the removed components in clearly marked plastic bags. The markings must ensure that the components can be installed exactly in their original places during assembly.

3. Turn the head over so that it is possible to install a clamp on it to compress the valve springs - usually the head is laid horizontally with the gasket surface towards the actuator and the valve springs away from it.



4. Insert the spring extractor into the plunger seat and compress the spring.

5. Using a screwdriver, remove the split lock crackers from their seat using a small magnet.

6. Release the clamp and remove the valve spring.

7. Remove the valve from the cylinder head. If so equipped, remove the oil seal.

Note: There are special tools for removing oil-deflecting caps. Alternatively, you can use regular needle-nose pliers - try not to damage the walls of the tappet socket, which can reduce the adequacy of the latter's fit.

8. If equipped, remove the adjusting washer from the spring - again use a magnet or screwdriver.

9. Proceed in a similar manner to remove the components of the remaining valves. Remember to place all components in clearly labeled containers or bags.

Lever-type pusher heads

1. To compress the valve springs on heads of this type, a special standard type tool is usually used. However, on some models there may not be enough free space to install such a tool - in such cases, you should use the clamp-type tool described above.

2. If you have not already done so, remove the valve train components (valve drive levers or rocker arms with their shafts) and take out the camshaft(s). If so equipped, also remove the hydraulic valve clearance adjusters.

Note: All removed components should be stored in an organized manner, paying particular attention to the clarity of the markings - when reassembling, they must be installed strictly in their original places!

3. Turn the head over to provide free space for installing the valve spring compressor tool.





4. After starting the tool, compress the spring of the first valve, completely unloading its plate.

Note: Due to the development of carbon deposits, the plate may "stick" to the split lock crackers and will have to be lightly tapped with a hammer to release it.

5. Using a small magnet, remove the split lock crackers from the valve stem groove.



6. Release the tool and remove the valve stem retainer and spring from the valve stem.



7. If equipped, remove the oil seal.

Note: It is usually easier to remove the valve stem seal with the valve removed from the engine (see below).

8. Turn the head over so that the valve can be removed from it.

9. Remove the valve from the cylinder head.

Note: If necessary, pre-treat the edges of the groove for installing crackers and the end of the valve stem with a fine-tooth file.

10. If equipped, remove the valve spring adjusting washer using a magnet or screwdriver.

11. Proceed in a similar manner to remove the remaining valves from the head. Remember to place all components in clearly labeled containers or bags.

Checking the status of components

After thoroughly washing and drying the valve mechanism components removed from the head, you can begin checking their condition. Some control measurements will need to be taken, for which you will need a micrometer with a jaw spread of 0÷25 mm - to measure the diameter of the valve stems, a plunger-type dial gauge / telescopic bore gauge - to measure the inner diameter of the guide bushings, a caliper and a special tool for assessing the degree of subsidence and the correctness of the valve spring facing. If you do not have the above tools at hand, you should entrust the inspection of the components to car service specialists.

Valves

1. Check the working chamfers of the valve plates for cracks, cavities and traces of excessive wear. Traces of burnout are most easily detected by examining the cylindrical part (belt) of the plate. The belt must be present on the plate without fail and have the same width along the entire perimeter of the valve. Rounding or melting of the edges of the belt indicates burnout of the valve. It is also necessary to assess the degree of non-flatness of the end surface of the plate - if there is excessive deflection in its central part, the valve must be replaced (preferably together with the others).

2. Next, you should check the condition of the valve stem tailpiece - carefully inspect its end and the edges of the groove for installing the split lock crackers - make sure there are no burrs or nicks (especially if you had to resort to processing these areas with a file when removing the valve). The end of the valve stem should be absolutely flat, while some rounding always occurs with significant mileage of the unit. If necessary, restore the flatness of the end by turning the valve.



3. Roll the valve stem on a flat surface (a window pane can serve as such) and check it for signs of bending.



4. Finally, measure the valve stem diameter in several places using a micrometer. Compare the measurements - the stem should have a uniform thickness along its entire length. If the minimum permissible deviation in valve stem diameter is not specified in the Specifications, the value of 0.025 mm should be taken as a guide.

5. Valves that are defective or worn beyond the permissible limit must be replaced (preferably in a set with the rest).

Valve springs, their holders and split lock crackers

1. First of all, check the valve springs for cracks, chips and other mechanical damage. Then measure the free length of the springs - try not to confuse the intake valve springs with the exhaust valve springs. Compare the measurement results with the requirements of the Specifications.



2. Using a ruler and a carpenter's square, assess the adequacy of the end cut of each spring.

3. If you have a special device at hand, check the force developed by the springs. Compare the results of the measurements with the requirements of the Specifications.

4. Sagging, defective and excessively worn springs must be replaced (preferably as a whole set).

5. Spring plates rarely need to be replaced, however, evaluate the condition of their working surfaces that contact the spring and split lock crackers. If signs of deformation or cracks are detected, replace them.

6. Assess the degree of wear of the internal and external working surfaces of the split lock crackers. If necessary, the crackers are replaced together with their valve.

Cylinder head

When inspecting the cylinder head, special attention should be paid to the condition of the guide bushings and valve seats. You should also check the head casting for cracks and other mechanical damage and assess the degree of non-flatness of the mating surfaces.

Valve guide bushings

1. Having made sure that the valves are in good condition, you should assess the degree of wear of the guide bushings by the size of the clearances where the valve stems fit in them.

Note: It is still preferable to replace the valves.

2. Before taking measurements, carefully inspect the guide bushings for cracks, burrs, burrs and other mechanical damage. When using removable bushings (on all heads made of aluminum alloy), evaluate the tightness of their fit - any slack is unacceptable. All bushings should protrude to the same height (counting from the spring seats).



3. Attach a plunger-type dial gauge to the spring side of the cylinder head. Lightly lubricate the valve stem and insert it into its proper place. Press the plunger of the gauge firmly against the side surface of the valve stem in the tailstock area and zero the gauge. Tug the valve from side to side in the guide bushing and read the gauge reading - record the result. Rotate the gauge 90° relative to its original position and repeat the check. After comparing the measurement results with each other, estimate the ovality of the guide bushing. Also compare the results of both measurements with the requirements of the Specifications.

Note: Special telescopic bore gauges are available for determining the internal diameter of valve guide bushings - when using such a device, compare the measurement results with the regulatory requirements given in the Specifications.

4. Worn or damaged guide bushings must be replaced or reground.

Valve seats

1. Visually inspect the valve seats. Look for cracks, cavities, and burn marks. Visually assess the seat depth in the head - excessive seating indicates component wear. If cracks are detected, the seats must be replaced.

2. If you have a special tool at hand, check the seats for signs of ovality. Compare the results of measurements with the requirements of the Specifications, if necessary, make a resurfacing.

Note: In the absence of standard values, the maximum permissible ovality should be considered to be 0.051 mm.

Evaluation of head flatness

1. Thoroughly clean the mating surfaces of the cylinder head, completely removing all traces of the old gasket material.

2. Flatness is checked using a special measuring device and a blade-type feeler gauge. Measurements are made along the DP of the head and along both diagonals of the mating surface.

Note: A steel ruler placed on its edge can be used as a flatness gauge.

3. If the amount of flatness exceeds 0.076 mm over a length of 15.2 mm (or 0.152 mm over the full length of the mating surface), the cylinder head must be resurfaced.

Note: After turning the cylinder heads of V-engines, the intake manifold mounting flange should also be turned accordingly to compensate for the change in the position of the mating surfaces.

Checking the condition of the head casting

1. Cracks in the head casting usually appear in the area of the combustion chambers, however, it is possible that they may also form near the spark plug holes, valve seats and the bearing surfaces of the valve drive levers.

2. Particular attention should be paid to checking the condition of the casting in the area of the outlet ports.

3. It should be remembered that visual inspection does not reveal hidden casting defects. A much more detailed picture of the head body structure can be obtained during flaw detection using magnetic resonance methods (Magnaflux®), - for heads made of cast iron, or using fluorescent compounds (Ziglo®), - for light alloy heads. Such checks can always be carried out at service stations for a very reasonable fee.

4. A head that has mechanical damage must be replaced.

Camshafts and valve lifters

For a description of the procedures for checking the condition of the camshafts and valve train components, see Section Removal and installation camshafts and valve lifters.

(The article is reprinted from a web resource MitsubishiMan)

Methods of component recovery

Most of the restoration procedures should be carried out in a car service workshop.

Lapping valves

Note: Valve grinding is performed last, after all components of the head have been checked and any necessary repairs/replacements have been made.

1. If the valves are considered fit for further use, it is necessary to machine the end surfaces of their tails and grind the working chamfers to their seats.

Note: New valves also need to be ground in, after which they become firmly attached to their seats.

2. Turn the cylinder head upside down.

3. Lightly lubricate the valve stems and install them into their proper places in the head.

4. Lift the valve to be lapped above the seat and apply a small amount of special lapping paste to the working surface of the latter.

5. Lightly wet the suction cup of the lapping holder and attach the latter to the flat side of the valve disc.

6. Rotate the tool's drive handle between your palms and begin to grind the valve against its seat. Try to frequently re-grip the handle, while slightly changing the position of the valve relative to the seat to avoid the formation of grooves.

7. Continue grinding until an even ring of matte gray color of the same width around the entire perimeter is formed on the working surface of the seat.

8. Separate the drive and proceed to grinding the next valve.

9. Finally, do not forget to thoroughly wipe the components, removing all traces of lapping paste and abrasive from their surface.

Springs, plates and crackers of split locks

10. The components listed in the subsection heading are not subject to repair and must be replaced if they fail.

Valve guide bushings

1. There are only two types of guide bushings used in automobile engines: removable (used in alloy heads) and built-in (used in heads made of cast iron).

Note: Cast iron heads are sometimes also supplied with removable bushings.

2. Restoration of worn guide bushings can be done in one of four ways: knurling; installation of inserts; boring and replacement.

3. During knurling, the metal of the part is deformed, which leads to a decrease in the gap. At the same time, the centering of the bushing is restored. Knurling is the simplest and cheapest method of restoring guide bushings, but it requires a special tool base and leads to a significant reduction in the service life of the restored part.

4. A bronze insert can be installed in a worn guide bushing after its preliminary boring. Inserts equipped with a thread are produced - to install them, the bushing must first be cut with a tap of the appropriate size. Alternatively, thin-walled bushings of a split type can be installed - they are inserted into a bored bushing, after which they are flared with a special tool and turned to the required size.

5. An effective method, especially when restoring built-in bushings, is to bore them for larger valves. Boring is done using a special countersink in the range from 0.076 to 0.762 mm (most often - 0.381 mm). It is necessary to purchase repair valves of the appropriate size.

6. To replace the built-in bushings, they must be drilled out of the head. Then the seats are bored to the required size and repair bushings are pressed into them. New bushings are installed using a hammer and a stepped drift. When installing the repair bushings, special attention should be paid to their centering relative to the valve seats. The mounting height of the new bushing must also strictly correspond to the original - do not forget to measure it before removing the old bushings. Old bushings are also knocked out of the head using a hammer and drift. Before installing the repair bushings, it is necessary to determine whether they should seal the water jacket of the head or not - if so, it is necessary to use an appropriate sealant, otherwise the bushing and the walls of the receiving seat should be lubricated with assembly grease before installation. The bushings are installed in the head from the side where the valve springs are installed.

Note: Using a set of process washers will help control the depth of the bushings.

Valve seats

Note: Valve seat resurfacing should only be performed after the valve guide installation parameters have been brought into compliance with the Specifications.

After replacing the guide bushings, the valve seats must be resurfaced!

1. If the valve seats are in satisfactory condition, then after grinding the valves (see above), you can begin assembling the cylinder head (see below).

2. Restoration of worn or damaged seats should be carried out in a car service workshop. When turning seats, special attention is paid to their centering relative to the valve guide bushings.

Cylinder head turning

When restoring a severely deformed head, the bearing journals of the camshaft(s) must also be subjected to a centering groove. Failure to comply with this requirement may result in serious internal damage to the engine when attempting to start it!

1. In case of particularly severe deformation of the mating surfaces, the head must be replaced.

2. Turning of the mating surfaces of the head (if necessary) should be carried out in a car service workshop.

Note: When removing the metal layer from the head surfaces during the turning process, the standard requirements for geometric parameters must be observed.

3. After returning the head from work, it must be thoroughly cleaned again (see above).

Sealing cracks in head casting

In some cases, a cracked cylinder head can be restored. Threaded inserts are installed along the crack in a cast iron head. When restoring light-alloy heads, welding is more effective, although the use of threaded inserts is also acceptable. Some defects can only be eliminated by soldering or welding - consult with car service specialists.

Assembly

First of all, it is necessary to prepare the workplace, paying special attention to the cleanliness of surfaces and the availability of sufficient free space. Take care to equip a place for storing the components to be installed. All parts to be installed must also be thoroughly cleaned and dried.

Cup-type tappet heads

1. To install recessed valve components in the tappet socket on heads of this type, you will need a small screwdriver, a valve spring clamp with a mandrel, some white grease (tsyatim) and a lot of patience.

2. Lightly lubricate the valve stems and install them in their original places in the cylinder head.

3. If equipped, install the valve spring adjusting washers in the correct positions.

4. Install new valve stem seals (if so equipped). If the seal is mounted on a guide bushing, lightly lubricate the outer surface of the latter beforehand. If a sealing ring is used instead of a sealing ring, install it after the valve spring has been compressed, but before the split lock crackers are mounted on the valve stem.

5. Place the spring and its plate on the valve stem.

6. Install the mandrel and compress the spring using a special clamp.

7. Using a screwdriver as a spatula, fill the bends of the split lock crackers with thick grease - this will help temporarily fix the crackers on the valve stem until the spring is released.

8. Using a screwdriver (again use grease), place the crackers in their regular places on the valve stem, pressing them tightly against the surface of the latter.

9. Slowly release the valve spring clamp, making sure that the crackers do not fall out, and remove it from the engine.

10. Proceed in a similar manner to install the components on the remaining valves.



11. Install the tappets, camshaft(s) (remember to check the valve clearances) and any other components removed during disassembly.

Lever-type pusher heads

1. Lightly lubricate the valve stems and install them in their proper places in the cylinder head.

2. If equipped, install the valve spring adjusting washers in the correct positions.

3. Install new valve stem seals (if so equipped). If the seal is mounted on a guide bushing, lightly lubricate the outer surface of the latter beforehand. If a sealing ring is used instead of a sealing ring, install it after the valve spring has been compressed, but before the split lock crackers are mounted on the valve stem.

4. Place the spring and its plate on the valve stem.

5. Using a special tool, compress the valve spring.

6. Place the split lock crackers on the valve stem.

7. Slowly release the valve spring, making sure that the crackers do not fall out of the groove on the valve stem.

8. Remove the spring compression tool from the head.

9. Proceed in a similar manner to install the components on the remaining valves.

10. Install the tappets, camshaft(s) (do not forget to adjust the valve clearances - see Chapter Settings and ongoing maintenance) and other components removed during dismantling.