Inspection of the cylinder head (Mazda Capella GD)

Check all cylinder parts for wear. Clean the cylinder head surfaces thoroughly (sometimes from the remnants of a previous compaction) - for this you need to use a scraper so as not to shave off the head material. Control and inspection shall be carried out in accordance with the following instructions.

2.4.3.1. Valve springs

To ensure perfect control of valve springs, it is necessary to use an appropriate device. If you don't have such a device, you can compare the used spring with a new one. To do this, both springs need to be clamped in a vice and pressed slowly. If both springs are compressed to the same size, then they have approximately the same tension. If the old spring is compressed to a shorter length than the new one, this is an indication of fatigue and the spring needs to be replaced.

The length of a spring in a tensioned state can be measured using a caliper. The length of the spring must correspond to the data in the table of parameters and overall dimensions. Figure 42 shows how springs are measured.





The springs are installed in order on a smooth surface so that the closed coil is at the bottom. Install a steel corner next to the spring. Measure the gap between the spring and the corner on the top side (figure 43), it should be no more than 1.8 mm for a camshaft engine or 1.6 mm for a diesel engine. On a DOHC engine, the outer spring can have a deflection of 14 mm, and the inner spring can have a deflection of 1.3 mm. Otherwise, the spring is skewed.

2.4.3.2. Valve guide bushings

Clean the guide bushings by wiping the inside with a rag soaked in gasoline. The best way to clean valve stems is with a rotating wire brush inserted into a power drill and the stem held against the brush. Insert the valves one by one into the corresponding holes. To control the play of the valve stems in the holes, a caliper and an internal dial indicator should be available:

• Using a dial indicator, measure the inside diameter of the guide bushings as shown in the figure 44. The obtained dimensions must be within the values given in the tables of parameters and overall dimensions. It is important to take into account the differences between individual engines.

(Based on website data mazbook)

• The outside diameter of the valve stems is measured in three places along the length, as shown in the figure 45. Once again, you need to take the data from the table of parameters and dimensions, but, in order to avoid errors, you need to ensure that they relate to the correct engine model. If the wear limits are reached, the valves and possibly the guide bushings will need to be replaced.

• Subtract the valve stem diameter from the inside bore size. The resulting dimension is the play of the valve stem in relation to the hole, which in all valves should not exceed 0.20 mm.
• If there is no internal dial indicator available, place a pointer indicator on the cylinder head as shown in the figure 46. Remove the valve from its seat and move the end of the valve stem up and down. The indicator sensor should be positioned as close to the end of the valve stem as possible. The measurement should not exceed 0.20 mm.

• Before changing the valve stems, you need to check the general condition of the cylinder head. Cylinder heads with minor scratches between the valve seats or between the valve seat and the first thread for the spark plug hole can be reused or ground, as long as the scratches are no wider than 0.5 mm. Cylinder head surfaces are inspected as described below (chapter 2.4.3.5). To replace the guide bushings, you need to knock out the old guides with a suitable mandrel from the top of the cylinder head. Before knocking out the guide bushings, the following instructions must be observed.
• Although the intake and exhaust valve guides look different, only the exhaust guides are installed when replacing them on an overhead camshaft engine. The DOHC engine has shorter exhaust valve bushings; the diesel engine has shorter exhaust valve guides.

Please note: Valve seats must be milled after the valve guide is replaced. If the seat can no longer be ground, then the guide bushings do not need to be changed.

• For standard 8-valve and diesel engines, a wire ring is inserted onto the outside of the guide bushing and applied to the top of the cylinder head. On this basis, the valve guide bushings are knocked out or pressed out only from the combustion chamber side. The guides for a 12-valve or DOHC engine are knocked out on this side. On these engines, however, the valve guide dimensions are measured before the guides are removed so that the new guides are driven to the same height. The cylinder head can be placed in boiling water until it reaches the temperature of the water. Place the head with the sealing surface on the workbench. The punch used for removal must rotate the pin that fits the inner surface of the guide bushing. If the valve guides are replaced, the valves are also replaced and the valve seats need to be ground. Clean the inner surfaces of the holes in the lower inner belt thoroughly and place the rings on the new guide bushings, if used. New guide bushings should be well greased and driven into the cylinder head, heated again to 100°C, from the camshaft side until the wire ring, if used, seats on the surface of the head. Drive the guide bushings without the wire ring until the pre-measured dimension is achieved, which is 19.8-20.3 mm for a 12-valve engine and 11.4-11.9 mm for a DOHC engine. The measurement is shown in the figure 47. A special mandrel is used for driving, but any mandrel with a trunnion can also be used. After pressing in, the guide bushings are reamed to a diameter whose size is adjusted depending on the engine type, with an allowance being made for the clearance between the valve stem and the bushings.

• Place the valve stem sealing ring onto the guide sleeve. Usually a special tool is used for this, as shown in the picture 48, however, a well-fitted piece of pipe can be used to break it, and the sealing ring will not be damaged.

2.4.3.3. Valve seats

• Valve seats should be checked for wear or scratches. Light signs of wear can be removed with a 45° milling cutter. If the seat is severely worn, it will need to be re-milled.
• The saddles depending on the obtained angle are shown in the figure 49 - top for petrol engine, bottom for diesel engine. The valve seat width for all gasoline engine valves should be 1.2-1.6 mm, and for diesel engines, 1.7-2.3 mm. As mentioned earlier, valve seats must be milled if new valve guides were used. First, you need to mill a 45° angle, and then lightly mill the top and bottom edges of the seat with the cutter shown in the picture to limit the width of the seat and move on to the inner surface. Milling work is completed as soon as the saddle reaches the specified width. Machined valve seats need to be ground. To do this, lubricate the seat surfaces with a small amount of grinding paste and insert the valve into the corresponding seat. Attach a suction device to the valve and move the valve back and forth.

After grinding, thoroughly clean all parts from dirt and grinding pads and check how the valve seat fits on the valve plate and the valve chamfer. The solid matte ring should be visible on both parts and forms the width of the valve seat.

Using a pencil, make several strokes around the circumference of the valve plate. The strokes must be at least 1 mm apart from each other. After this, carefully insert the valve into the guide bushing and seat, turn the valve 90°, and a certain pressure will be applied to it (in this case, a suction pipe is used).

The valves are removed again and checked to see if the pencil marks have disappeared from the circumference of the seat. If the valve seat spring is within the specified dimensions, the head can be reinstalled. Otherwise, the saddle will need to be adjusted, or, as a last resort, a spare head will need to be installed.

Note: If the valves and seats are subject to repeated reworking, or if the seats are deeply recessed into the cylinder head, it is necessary to measure this depth in order to obtain good seats. In gasoline and diesel engines this work is performed differently:

For a standard petrol engine, insert the valves into the guide bushings one by one and, as shown in the figure, 50. Measure the "L" dimension. For a standard 8-valve engine, the dimension should be 46.5 mm; if the engine has 12 valves, it should be 50.2 mm. Depending on the obtained values, the following measures can be taken:

• if the "L" dimension is 46.5-48.0 mm for an 8-valve engine or 50.2-51.0 mm for a 12-valve engine, the cylinder head can be reinstalled;
• if the "L" dimension is 48.0-48.7 mm for an 8-valve engine or 51.0-51.7 mm for a 12-valve engine, an adjusting washer must be inserted between the lower valve seat and the cylinder head to equalize the distance;
• if the size exceeds the specified limits, replace the cylinder head.

For a DOHC engine, the measurement is carried out using the indicators in the figure 50 ways and depending on the results obtained:

• if the "L" dimension is less than 36.8-37.6 mm, the cylinder head can be installed again;
• if the size is between 37.6 and 38.3 mm, an adjusting washer is inserted between the spring seat and the cylinder head;
• if the dimension "L" is less than 38.3 mm, the cylinder head must be replaced.

In a diesel engine, measurement is carried out in different ways. The measurement is taken from the top side of the cylinder head. Depending on how far the valve plate is worked into the seat:

• insert the valves into the seats one by one and press firmly;
• using a measuring probe and a ruler, as shown in the figure 51. The dimension between the top side of the valve plate and the surface of the cylinder head is measured. The nominal size is 0.75-1.05 mm, with a wear limit of 2.55 mm;
• if the size is between 1.55 and 2.55 mm, an adjusting washer is placed under the valve spring plate. If the wear limit is exceeded, the cylinder head must be replaced.

2.4.3.4. Valves

Minor damage to the valve head surface can be repaired by grinding the valves in the cylinder head seats as described above. The valves must be measured in accordance with the table of parameters and dimensions, and all valves that do not meet these parameters must be replaced.

If the valve stem ends are worn, they can be ground on a grinding machine, provided that less than 0.50 mm is removed for adjustment. Valve heads can be ground on a grinding machine, provided that the valve head edge dimension is as shown in the figure 52 between the arrows is 0.5 mm for the intake valve or 1.0 mm for the exhaust valve if the valves are to be used again. This value is for standard engines. For a DOHC engine, it is 0.85 mm for the intake valves and 0.9 mm for the exhaust valves; for diesel engines, both types of valves require an additional 0.8 mm. The grinding angle is set to 44.5° (the valve plate angle is slightly less than the valve seat angle).

2.4.3.5. Cylinder head

Thoroughly clean the sealing surfaces of the cylinder head and the cylinder block and check the cylinder head plane for warpage. To do this, place the measuring ruler on the head (figure 53) and using a measuring probe, determine the clearance along, across and diagonally across the plane of the cylinder head. If the sheet gauge can be inserted more than 0.15 mm thick for a gasoline engine or 0.1 mm for a diesel engine, then the plane of the cylinder head for a gasoline engine is planned to be ground, but in compliance with the minimum permissible height of the cylinder head.



Standard gasoline engine: 91.9592.5 mm (grinding size max. 0.20 mm) DOHC engine: 133.95-134.05 mm (grinding size max 0.20 mm). The cylinder head of a diesel engine must also have a height of 133.9-134.1 mm. However, it cannot be ground. While the cylinder head of a gasoline engine is being ground, the valve seats need to be checked (they cannot be milled too deep) and, in addition, it is necessary to measure the clearance of the camshaft journals in the bearings, since exceeding the permissible clearance requires replacing the head. The gap may in no case be greater than the specified maximum value.

2.4.3.6. Camshaft

Place the camshaft with both ends of the bearing journals on the prisms, as shown in the figure 54, or clamp it in the center of the lathe and install the dial indicator on one of the middle bearing journals. Slowly turn the camshaft and read the readings on the dial indicator. If the readings at full rotation are more than 0.03 mm for a gasoline engine or 0.10 mm for a diesel engine, then the camshaft must be replaced, as it cannot be repaired. Next, you need to check the bearing journals and camshaft surfaces for visible damage. If they look good, you need to measure the cam height and bearing clearance:



To measure the height of the cams, proceed as shown in the figure 55. The height of the cams varies for different engines and is determined according to tables of parameters and overall dimensions. Of course, you need to look at the data of the corresponding engine. There is also a difference for engines running on unleaded gasoline.



Before checking bearing clearances, check the bearing caps for damage. If the covers are damaged, the covers, camshaft and cylinder head must be replaced.

Thoroughly clean the cylinder heads and camshaft journals and arrange the heads according to bearing numbers.

The clearance in the bearings is measured using a plastic wire "Plastigage". Use a piece of this wire to wrap all the bearing journals across the entire width and insert the caps one by one into the cylinder head.

Carefully hammer the caps and insert the bolts. Tighten the bolts to the specified torque, working from the middle outwards to compress the plastic wire across its width. For engines with two camshafts, the exact sequence for tightening the bearing caps must be observed, which can be taken from the figure 56. The camshaft(s) no longer need to be turned.



Unscrew the bearing caps again, but this time start from the outer edge of the bearing caps. Immediately check if there is a wire hanging on the lid "Plastigage". In this case, it may still stick to the bearing journal.

Use a template to measure the width of the pressed plastic strip at its widest point, as shown in the figure 57. The measurement is carried out in the same way for all engines. This ensures the smallest possible bearing clearance. If the clearance is greater than 0.15 mm or 0.10 mm on a diesel engine, the cylinder head and/or camshaft must be replaced to return the clearance to a value within the individual bearing range. Standard engines have different clearances for the front, three middle and rear bearings. In a DOHC or diesel engine, the clearance of all bearing journals is the same, if necessary (see tables of parameters and dimensions).



To measure the maximum clearance of the camshaft, it is inserted into the cylinder head and a dial indicator is installed in front of the head. The dial indicator probe is installed against the end surface of the camshaft, as shown in the figure 58, and the indicator is set to zero if the shaft is pressed on one side. Move the shaft back and forth and read the dial indicator. If the wear value has reached 0.20 mm, then the camshaft must be replaced, or in the worst case, the cylinder head. For a DOHC engine, of course, both camshafts need to be measured.

Note: If the valves have been ground, they must fit into the corresponding seats, as the grinding pattern is different for all valves.

2.4.3.7. Rocker arm mechanism (standard engine)

Light wear on the ends of the rocker arm can be removed by lightly sanding them on a grinding machine. If the wear limit is exceeded, a new rocker arm is required. The rocker arm is checked at the points of connection with the valve stem. If the rocker arm is suspected of being misaligned at the drilled locations, the shaft diameter and the inner diameter of the hole must be replaced. If the wear limit of 0.10 mm is reached, the parts must be replaced.

The hydraulic system of the 12-valve engine must be checked for wear or damage. If necessary, replace the rocker arm. The devices are located at the edges of the rocker arm.

2.4.3.8. Hydraulic tappets (DOHC engine)

Each pusher should be squeezed in turn between the thumb and index finger. If the pusher has shifted, it must be replaced. Other damage may occur at lapping points or on working surfaces.

2.4.3.9. Tappets and tappet washers (diesel engine)

Measure the outside diameter of each tappet and the inside diameter of the corresponding holes. If the difference is more than 0.1 mm, the cylinder head tappet is replaced, depending on where the wear has occurred.

2.4.3.10. Combustion chamber bushings (diesel engine)

The combustion chamber bushings are pressed into the cylinder head and cannot be replaced. Replacing the bushings requires replacing the entire cylinder head. The combustion chambers must not protrude more than 0.005 mm above the cylinder head and must end no more than 0.02 mm below the cylinder head surface. A dial indicator is used for inspection and is placed above the cylinder head surface on the top side of the bushing, as shown in the figure 59.

2.4.3.11. Drive belt and drive gear

A belt with worn teeth must be replaced. Other defects include scratches, abrasion of planes, or rounding of one or all teeth. In these cases, it is necessary to check the teeth of the drive gear. Hold the drive belt tensioner with one hand and turn the roller with the other. If the adjustment is difficult, the tensioner must be replaced. Under no circumstances should the tensioner be cleaned with cleaning liquids. Measure the length of the return spring for the tensioner. The measurement should be taken from the inner curve of the spring coil. The following dimensions are considered valid: for a standard carburetor engine - 61.0 mm, for a standard pump-carburetor engine - 56.9 mm, for a DOHC engine - 53.3 mm and for a diesel engine - 52.6 mm.