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Valve guide's getting depressed
It gets depressed because the valve guide who had been press-fit becomes loose by the cylinder head's overheating, it comes in contact with the neck of the valve, and breakage of the valve is generated.
Case thought about as factor of cylinder head overheating ･Cooling shortage because of removing, and processing of flywheel of engine (cooler fan) ･Obstruction of cooling style by engine cover ･The head might overheat when oil doesn't take effect enough to the head. (In this case, even if the temperature of oil is checked, the temperature of oil might not notice because it doesn't go up. ) ･The fuel passes and the Japanese pampas grass passes. In addition, the match of showing high power and [ekipai] and the muffler is thought.
	1.Normal valve guide	2.Valve guide who is depressed
	3.Normal valve guide	4.Valve guide who is depressed
バルブガイド出代１．０ mm
The check method can do nothing but remove spring, measure valve guide's [dadai], and it be likely to be understood that there is a head new (normality) when peeping from the exhaust port, and comparing it as shown in the above-mentioned photograph.

5.After contact with the valve guide