Cylinder head repair (Opel Frontera B)

Disassembly

Remove the cylinder head (see the relevant chapter).

Warning. Before removing the camshaft bearing caps, check the caps for markings or mark them.

Working in a spiral from the outside to the inside, loosen the camshaft bearing cap bolts one-half turn or one turn at a time to gradually relieve the valve spring pressure on the bearing caps. Remove the bolts and bearing caps.



Using the special tool KM-845, remove the hydraulic valve clearance compensators. Do not mix up hydraulic valve clearance compensators from different cylinders, which may lead to accelerated wear.



Label the valves. Using a special device KM-348 (1) with an adapter KM-653 (2), compress the valve spring and remove the crackers from the valve stem.



Remove the valve spring retainer and valve spring.

Using the special tool KM-840, remove the oil deflector cap.



Remove the remaining valves from the cylinder head in the same manner.

Check the mating surfaces of the cylinder head and the working surfaces of the valve guide bushings and plain bearings for wear.

Examination

Cylinder head

Using a metal ruler and feeler gauge, check the flatness of the cylinder head surfaces in several directions.



Measure the height (I) of the cylinder head.





Cylinder head height: 134 mm

Checking the clearance between the valve guide and the valve stem

Using the MKM-571-V bore gauge, measure the inner diameter of the valve guide bushings in several places.



Using a micrometer, measure the diameter of the valve stem in several places along the height.

Calculate the clearance between the valve guide and the valve stem. To do this, subtract the outside diameter of the valve stem from the inside diameter of the corresponding valve guide.

Example:

• Valve guide inner diameter: 6.012 mm
• Valve stem outside diameter: 5.972 mm
• Clearance between valve guide and valve stem: 0.040 mm

Nominal clearance between valve guide and valve stem:

• inlet valves: 0.030-0.057 mm
• exhaust valves: 0.040-0.067 mm

Valve grinding

If the valves are in satisfactory condition, they should be ground to the seats to ensure a tight seal that prevents gas leakage. If the seats have only minor damage or the seat has been reground, lapping can be done using a fine abrasive paste. Coarse lapping paste should only be used if traces of deep wear or severe burnout of the seats are detected. In this case, the cylinder head and valves should be checked by an experienced technician to determine whether the seats need to be machined or replaced.

The valve grinding is performed as follows. Place the cylinder head on a flat surface with the combustion chambers facing upward.

Source is on the website: Opelbook.ru

Apply lapping paste to the valve plate and valve seat, install the valve in place and install the suction cup with handle on the valve plate. Rotate the valve with a suction cup in different directions to grind the valve, and periodically lift the valve to redistribute the grinding paste. Lapping is made much easier if a not very stiff spring is placed under the valve head.



If a coarse lapping compound is used, lapping should be carried out until a uniform matte surface appears on the valve seat and valve. Then wipe off the used paste composition and repeat the lapping process with a fine paste. Continue grinding until a light grey-matte colour appears. Further grinding is not allowed, since excessive wear of the seat may make subsequent repair impossible.



To check the valve grinding, apply red lead primer evenly around the working edge of the valve plate, then insert the valve into the guide bushing and turn it 90°, while pressing lightly on the valve.

Remove the valve and check for streaks. If all the lines are erased, the valve can be finally installed. Otherwise, it is necessary to repeat the lapping operation.

After finishing grinding all valves, remove any remaining abrasive material by thoroughly rinsing all parts with clean kerosene or solvent.

Increasing the internal diameter of the valve guide bushing

Using the MKM-571-V bore gauge, measure the inner diameter of the valve guide bushings in several places.

Warning:

• The engine may be equipped with larger diameter valve guides.
• Identification of the oversized size: the code letter K1 is stamped on the valve guide sleeve and on the end of the valve stem.

To obtain the next 0.075 mm increase in the internal diameter of the valve guide bushing, use a special tool (reamer) KM-805. After processing the internal diameter of the valve guide bushing, cross out the stamped code and stamp out a new diameter code.

Replacing the valve seat

Arc weld a metal rod to the inside surface of the valve seat, being careful not to damage the cylinder head.



Wait a few minutes for the valve seat to cool down, during which time the valve seat will decrease in diameter due to the coefficient of thermal expansion.

Use the welded metal rod to remove the valve seat from the cylinder head.

Clean the valve seat thoroughly.

Heat the cylinder head, which will cause the valve seat to increase in size due to the coefficient of thermal expansion.

Cool the new valve seat with dry ice, this will cause the valve seat to shrink in size due to the coefficient of thermal expansion.

Using a press, press the new valve seat into the cylinder head socket.



After pressing, process the working edges of the new valve seat, while precisely maintaining the working angle of the valve seat and the width of the working chamfer. Ensure that the valve seat insert surface contacts the entire working surface of the valve disc.

Lap the valve to the valve seat.

Assembly

Clean the parts before installation.

Apply a thin coat of engine oil to the valve stems and install the valves in their original locations in the cylinder head.

Install the special device KM-835-A (4) on the valve stem and install the oil deflector cap (3) along it as a guide.

Notes:

• Do not reuse previously removed valve stem seals.
• Incorrect installation of the valve stem seal will adversely affect its working edge due to eccentricity and will result in engine oil leakage through the valve guide. When installing, be careful not to twist the oil seal.

Install the valve spring and spring retainer.

Using a special device KM-348 (1) with an adapter KM-653 (2), compress the spring. Install the crackers and remove the special spring compressor. Using a plastic hammer or hammer handle, tap the end of the valve stem several times to seat the crackers in place.





Further assembly is carried out in the reverse order of disassembly.

Install the cylinder head (see the relevant chapter).