Because each maintenance personnel has different understanding of excavator maintenance, there are some misunderstandings in the maintenance process. This article will explain the misunderstandings existing in the maintenance process for reference only.
1. New cylinder liners and pistons are installed without selection
When replacing the cylinder liner and piston, it is considered that the new cylinder liner and piston are standard parts, which are interchangeable and can be used when installed. In fact, the dimensions of cylinder liner and piston have a certain tolerance range. If the cylinder liner with the largest size is equipped with the piston with the smallest size, the matching clearance will be too large, resulting in weak compression and difficult starting.
Therefore, the size grouping code of standard cylinder liner and piston must be checked during replacement. The installed cylinder liner and piston must make the size grouping code of standard piston the same as that of standard cylinder liner. Only in this way can we ensure that there is a standard fit gap between them.
In addition, when installing cylinder liners and pistons with the same group code, pay attention to the inspection of cylinder plug clearance before installation. In order to ensure the assembly standard, a test shall be carried out before installation to prevent the installation of fake and inferior defective products.
2. Inaccurate measurement of cylinder clearance
When measuring the cylinder clearance, it cannot be measured in the direction that the piston skirt is perpendicular to the piston pin hole, but in other directions. The structural feature of aluminum alloy piston is that the upper part is small and the lower part is large as a cone, and the skirt section is oval, so the cylinder clearance along the circumferential direction is not equal.
When measuring, the clearance in the direction of the long axis of the ellipse shall prevail, that is, the clearance of the piston skirt perpendicular to the piston pin hole shall be measured. This measurement is more convenient and accurate, and in the reciprocating motion, the piston skirt perpendicular to the piston pin hole is greatly worn due to the action of lateral pressure. Therefore, when measuring the cylinder clearance, it should be measured in the direction of the piston skirt perpendicular to the piston pin hole.
