A,

 Strong noises from engine valves or valve drive components The possible causes and solutions are as follows.

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    (1) The valve spring is broken. Replace damaged parts. 

 (2) The camshaft is broken. Replace damaged parts. Thoroughly clean the engine. 

 (3) The valve lifter is damaged. Thoroughly clean the engine. Replace camshaft and tappet. Look for valves that are not moving freely. Adjust the valve clearance to the correct valve clearance value.

  (4) The valve is damaged. Replace damaged valves. Make adjustments if necessary.

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 B

. The rocker arm hardly moves, and the valve clearance is too large The possible causes and solutions are as follows.  

 (1) Insufficient lubrication. Check the lubrication of the valve chamber. At high engine speeds, the oil flow should be large; at low engine speeds, the oil flow should be small. The oil passage must be clean, especially the oil passage that sends the oil to the cylinder head. 

 (2) The rocker shaft is worn . If the wear is excessive, install new components or rocker arms. Adjust the valve clearance. 

 (3) The end of the valve stem is worn. If the valve stem end is too worn, install a new valve. Adjust the valve clearance. 

 (4) The valve clearance is too large. Adjust the valve clearance.  

(5) The push rod is worn. If the push rod is too worn, install a new push rod. Adjust the valve clearance.

(6) Tappet wear. If the lifter assembly is too worn, install a new lifter assembly. Adjust valve clearance.