The reaming of valve seat of Cummins Diesel generator is applicable to soft valve seat, which is usually carried out with valve seat reamer. A pair of valve seat reamers generally have four angles: 15 °, 30 °, 45 °, and 75 ° (or 60 °). The 30 ° and 45 ° reamers are further divided into two types: coarse blade and fine blade. Generally, the coarse blade has a tooth shape and is used for preliminary reaming. When a certain degree of reaming is achieved, a fine blade reamer is used for precision machining.
Before reaming, it should also be noted that because the valve seat is reamed based on the valve guide, if the valve guide needs to be replaced or reamed, it should be done before the valve seat is reamed. Otherwise, if the valve seat is first reamed before replacing or fitting the guide tube, it may cause the center of the seat and tube to shift, resulting in the valve not being able to fit with the seat.
The general reaming process of Cummins Diesel generator is as follows:
(1) Select the reamer guide rod according to the inner diameter of the valve guide, select the appropriate reamer guide rod, and insert it into the valve guide, so that the guide rod fits with the surface of the valve guide hole.
(2) Due to the presence of a hardened layer in the valve seat, the reamer often slips during reaming. In this case, a coarse sandcloth can be used to pad under the reamer for sanding before reaming.
(3) For initial reaming, first place a 45 ° reamer (depending on the situation) on the guide rod, aligning the keyway of the reamer with the flange of the lower end face of the reamer handle, and then proceed with reaming. When reaming, the reamer should be straight, and the force on both hands should be uniform and stable. Rotate the reaming clockwise. When turning the tool counterclockwise, do not use force to prevent the blade from becoming blunt until defects such as ablation, spots, and dents on the valve seat are removed.
(4) After the initial hinge of the contact surface for trial assembly and repair, the matched valve that has been polished should be used for trial assembly. The method is to apply red lead oil to the conical working surface of the valve seat, place it in the guide tube and rotate it for 2-3 turns (do not pat), then take out the valve and observe its contact condition.
The normal requirement is that the contact surface should be located in the middle and lower part of the valve operation slope, with a width of approximately 1.0~2.0mm for the inlet valve and 1.5~2.5mm for the exhaust valve. If the contact surface is too narrow, it will affect sealing and heat dissipation. If it is too wide, it is easy to accumulate carbon and cannot fit tightly. In the middle and lower part of the conical working surface of the valve, the width is 1.5-2mm. After initial reaming, if the contact surface is upward, a 15 ° reamer should be used to ream the upper port to move the contact surface downward. If the contact surface is downward, a 75 ° reamer should be used to ream the lower port to move the contact surface upward. During initial reaming, the valve contact surface should be as low as possible in the middle and should be tested while reaming. In order to extend the service life of the valve seat and valve, the mating can be stopped when the contact surface is Imm from the lower edge of the valve.
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