How to replace the cylinder head gasket
After it is determined that the cylinder head gasket is ablated, it should be replaced according to the correct force method to improve the sealing quality of the cylinder head gasket.
(1) When removing the cylinder head bolts, it is necessary to wait for the engine to be completely cold-sealed before proceeding. When removing, follow the principle of "evenly loosening from both sides to the middle diagonally" to prevent the cylinder head from warping and deforming.
(2) Remove the old cylinder gasket, clean the cylinder head and the sealing surface of the cylinder block.
This work requires special patience and meticulousness. It is necessary to thoroughly remove the old sealant, carbon deposits and corrosion products on the sealing surface, and blow it with compressed air.
(3) Check whether the sealing surface of the cylinder head and the cylinder block is deformed.
Check the longitudinal and transverse directions of the sealing surface with a ruler and a thickness gauge. Generally, the unevenness of the sealing surface of the cylinder block and the cylinder head is required to be no more than 0.10mm along the entire length, and no more than 0.03 in any 100mm length. mm must not have any raised or recessed parts on the sealing surface. Check that the height of the upper end face of the cylinder liner higher than the upper plane of the cylinder block should be within the specified range of 0.05~0.15mm.
(4) The selected cylinder head gasket must be original parts that meet the requirements and have reliable quality
When installing, pay attention to its installation direction. The basic principle is that the curling edge is facing the contact surface or hard plane which is easy to be trimmed.
The specific instructions are as follows:
①If the cylinder head gasket itself has an installation mark, install it according to the installation mark.
②No mark, the cylinder head is cast iron, and the curling edge faces the cylinder head. When the cylinder head is cast aluminum, the curling edge should face the cylinder block. When the cylinder head and cylinder body are all cast aluminum, the curling edge should face the convex edge of the wet cylinder liner.
(5) Tightening method of cylinder head bolts:
The tightening of the cylinder head bolts is the most important part to ensure the sealing quality of the cylinder head gasket. The specification of this operation directly affects the sealing quality of the cylinder head gasket. It must be operated in strict accordance with the technical standards. At the same time, there are some details that must be Pay attention:
① Thoroughly clean up the sludge, carbon deposits, coolant, oil and other sundries and liquids in the bolt holes, clean the threads with a tap if necessary, and blow them with compressed air.
② Thoroughly clean the bolts of the cylinder head, carefully check the bolts, if there are cracks, pitting and necking, they should be scrapped and cannot be used further. Use a caliper to measure the length of the bolt in the free state. If the plastic deformation of the bolt exceeds 1.5%, it can no longer be used. There are also some engine manufacturers that tighten the bolts to the yield point of the material when tightening the cylinder head bolts. In this way, a more consistent clamping force can be formed on the cylinder head to ensure the reliable sealing of the cylinder head gasket. Therefore, the bolts are designed to be used only once and must be replaced after disassembly.
If old bolts are used and re-tightened to the yield point of the material, a "weak point" will be created, causing the cylinder head gasket to fail.
③ Before installing the cylinder head bolts, apply a little oil on the threaded part and the flange support surface to reduce the dry friction at the threaded pair.
④For the split cylinder head, install the water distribution pipe and the intake pipe on the cylinder head before tightening the cylinder head bolts (without gaskets), and tighten them according to the specified torque, otherwise, the sides of the cylinder head may not be the same. Water leakage or air leakage occurs on the plane.
⑤ Tighten the cylinder head bolts according to the technical specifications. The tightening methods and torques of various engine cylinder head bolts are different. The general principle is to expand and cross symmetrically from the middle to both sides, and tighten them to the specified torque in 2 to 4 times. Repeat tightening.
⑥Due to the different expansion coefficients of materials, in order to prevent the expansion of the cylinder head bolts after heating from being greater than the expansion of the cast iron cylinder head and reducing the compactness, the cast iron cylinder head should be tightened a second time when the engine reaches the normal working temperature. Since the expansion coefficient of the aluminum alloy cylinder head is greater than that of steel, the pressing force will be greater after the engine is hot, so it only needs to be tightened once in a cold state.
