Repair of Cylinder Head

Common damages to the cylinder head include warping, ablation, cracks, etc.

1. Detection and correction of the flatness of the cylinder head

The deformation of the cylinder head plane is due to improper tempering during the casting process, uneven torque of the tightening bolts during installation or removal during repair (especially hot cars) caused by improper placement.

1) Measurement method
Place the knife edge ruler on the plane of the cylinder head, and use a thickness gauge to test at the seam gland. Within the range of 50mmX 50mm, the flatness error of the lower plane of the cylinder head of the side valve engine should not be greater than 0.05mm.

2) Calibration method
Place the deformed protruding surface of the cylinder on a flat plate, pad with 0.5~0,7mm thick gaskets under both ends, and then pressurize the convex surface with a press or screw, and at the same time use a blowtorch to pressurize the deformed part. Heat to 300-400C, when the cylinder and the plate are attached, keep it cool, and remove it for retesting. If there is local deformation, use the scraping method

2. Measurement and adjustment of combustion chamber volume.

After the cylinder head plane is ground, the volume of the combustion chamber will become smaller, and local corrosion will also affect the change of the combustion chamber volume. When the combustion chamber volume exceeds the original specification, it will affect the Stability at idle speed. Therefore, measurements and adjustments must be made.

1) Measurement method
The measurement of the volume of the combustion chamber of the cylinder head should be carried out after the oil dirt, carbon deposits and glue in the combustion chamber are completely removed, and the cylinder head should be in a horizontal position. Generally, water or mixed liquid (80% kerosene and 20% engine oil) is used as the measuring liquid. When measuring, inject an object with a certain volume, and reflect the volume through a pressure gauge.

2) Calibration method
Small volume: a layer of metal can be milled off at the bottom of the combustion chamber, or a layer of surface can be etched off by electro-erosion. The volume is too large: the welding layer metal can be added to the side wall of the combustion chamber.

3. Precautions when removing and installing cylinder head bolts

Using the correct operating procedures to disassemble and assemble the cylinder head bolts is an effective measure to prevent the deformation of the cylinder head and damage to the cylinder head gasket. When disassembling and assembling the cylinder head bolts, it should be carried out in the order specified by the original factory. If there is no original specification, the dismantling bolts should be loosened several times from both ends to the middle: when assembling, they should be tightened sequentially from the middle to both ends, preferably three times. The first time is to tighten them in sequence; the second time is to tighten by two-thirds of the specified torque. Removing the cylinder head should be done after the engine has cooled down. The tightening torque of the cylinder head bolts shall be tightened according to the original standard.