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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Lapping and cutting the seat are 2 totally different things, when you lap in valves it will make a ring all around the seat but that is not the measurement you take. The valve seating surface area is generally .040", the first angle is usually 30 to 32 degrees, the second angle (Seating surface) is 45 degrees and should only be 040" wide, and the third angle is 60 degrees, you need to use valve seat cutters with the correct angles or take the head to a machine shop that really knows what they're doing and have the seats cut. Also, I know the Yamaha manual says to lap the valves but it's the worst thing you can do to ti valves, all ti valves have a coating on them that dissipates heat, when this coating wears off the valves will start to move, the lapping compound take this coating off in the lapping process. You need to cut the seats correctly and do not lap in the valves, if the seats are cut correctly there is no need to lap in the valves anyway.