Valve guides have a hard time on these single overhead cam engines, quite often revved hard from cold, before the oil has reached the cylinder head. Smoking on the overrun, or after ticking over is indicative of worn valve guides. Replacing with new genuine Honda items, whenever you re-build and engine, or just a cylinder head overhaul is good practice, fitting new Honda valves is also recommended at the same time
Note: this part is superseded by 12023465405.
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