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Old 11-07-2010, 07:16 PM   #34
bikecat OP
Beastly Adventurer
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Joined: Jan 2006
Location: Tropical Far East
Oddometer: 1,123
Originally Posted by bmwrench
Those look like Black Diamond valves to me. The black coating often wears on the stem, particularly at the bottom and to a lesser degree at the top-which is where all valve stems wear. It doesn't seem to hurt anything as the stem itself is supposed be nitrided. The thing to watch for on these valves is transfer of guide material to the stem. If this is the case, both valve and guide should be replaced. If no metal has transferred and you measure clearance, be aware that this assembly needs at least .003" clearance to survive.

The right piston crown indicates that it has had water in it-probably from the crankcase vent. I'd bet that the top ring started to rust to the bore at some point and that the ring broke when the motor was started.

Some history might help. The bike stood in tropical weather for nearly 3 years between 2003 to 2005 and then another 3 years in the workshop while the rebuild was taking place.

This is a steep learning curve for me (I have no mechanical background), and I am grateful for the advice given.

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