Marine diesel engine parts introduction - Inspection and maintenance of valves 

Main Maintenance Techniques for Valve and Valve Seat of DK28 Diesel Engine Components 

Before the maintenance, measure whether the distance between the bottom surface of the valve and the bottom surface of the cylinder cover exceeds the specified limit. If this value differs greatly, it will affect the compression ratio of the diesel engine and cause the valve to collide with the piston. Therefore, the valve seat pad must be replaced. During the maintenance, for the valves that have been working for a long time, the following measurements should be conducted: the roundness error and cylindricity error of the valve stem after wear. These errors can be obtained through measurement and inspection with an outside diameter micrometer, etc. When these two errors exceed 50% of the limit of the clearance with the guide tube, they should be scrapped and replaced; the radial runout of the conical surface relative to the outer cylindrical surface of the valve stem should not be greater than 0.003mm. Otherwise, they should be scrapped and replaced. 

During the inspection, place the valve stem support between the main spindle head of the lathe and the tail support pin. Both the pins should be placed in the original processing pin holes of the valve. Place the dial indicator on the slide plate and make the contact points of the dial indicator touch the conical surface of the valve. During one rotation of the valve, the maximum change in the reading of the dial indicator is the radial runout. At this time, check the cracks, spots and pits of the valve by clamping the valve and conducting the inspection. The outer surface of the valve stem is allowed to have up to 10 lines with a length not exceeding 20mm. Magnetic particle inspection should be carried out on the conical surface and the joint and locking clamp of the valve stem, and the magnetism should be removed. Valves with cracks should be scrapped.