If the noise is clearly visible, the camshaft and tappets should be replaced.
Removal
1. Remove the cylinder head cover.
2. Remove the rocker arm with the shaft and take out the rod in the cylinder in which the operation of the pusher is accompanied by abnormal noise.
3. Remove the side cover and take out the plunger.
4. Store the tappets in the order they were installed.
Examination
1. Wash the plungers one by one.
2. Check the wear of the pushrod thrust surface, rod seat and side surface condition. Replace the pushrods if the thrust surface shows galling, scratches or increased concavity.
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3. The thrust surface of the pusher has a concavity with a large radius of curvature (the photo on the left shows the check of the concavity of the thrust surface of the pusher). If the thrust surface is badly worn (photo on the right), then the camshaft and tappets should be replaced. If the side surface is worn (which is unlikely), then check the condition of the holes in the cylinder block. Check the condition of the rod seats and the ends of the rods themselves.
4. The camshaft and tappets are changed only together. Removed tappets should be put back in their original places.
Installation
1. Lubricate the tappets with molybdenum grease.
2. Lubricate the cylinder block bores with engine oil.
3. Install the pushers into place.
4. Install the remaining removed parts in reverse order.