Quote:
Originally Posted by punkinrider55
When we did put all 5 new valves in I did use lapping compound and cut new seats for the new valves...after lapping them u can see where the compound was hitting the seat and it has a perfect ring all the way around and was in thickness per the manual spec (cant think of it off the top of my head). It didnt get thinner at one part of the valve and then thicker at the other. It was an even ring all the way around.
This bike was a valve recall bike and the center valve broke in a very odd place. it broke about .5CM off the stem of the valve where the keepers ride and hold the valve up. (let me know if you understand that kinda hard to explain) maybe Anthony can chime in but there wasn't but 20hrs on the bike when that valve broke so i figured the seats were ok and it was just a bad valve.
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By lapping the valves, you're taking off the sub-par coating Yamaha put on them, exposing uncoated Ti material which actually doesn't make a good valve material to begin with. Ti does not like heat, and isn't an impact resistant material. As soon as that coating is gone, you can expect a very short life for that valve. The value in most high quality aftermarket Ti valves is in the coating.
You're right, that is an odd place for the valve to break...they usually break where the radius from the backside of the valve merges into the stem. New valves always need the seats recut to get the 2 surfaces to mate well and create a good seal.