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Valves get "tighter" with age as the seat wears from the pounding of the valve. This causes the stem to sit up higher into the port of the head and the clearance to the rocker arm to be reduced
Yes, this is correct and the idea that "noisy valves just need to be adjusted" is usually false. Chasing noise by closing the clearances is bad advice. Noise from wear in the guides and rockers cannot be adjusted out. The valve clearance gets wider when the engine is hot. The clearance spec is not about thermal expansion, it is about the amount of time the valve gets to sit down and give off heat through the seat. The factory spec should be considered the minimum and there is no good reason to ever set them tighter.
Paul
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Paul
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