Valve grinding.

[th62]

Valve grinding.
I ground the valves in but they still leaked. So I pulled them and found the seats way to wide, they won't seal if too wide. Yamaha says, 1.3mm. So I mounted the valves on the lathe and using a drum sander in a rotary tool ground the back of the valve down so the seat was 1.2mm wide. The edges are around .5mm or better.
I sent off for a 30 degree cutter head a while back, but didn't have a handle for it, so turned up a handle from stainleas with a 10/11mm taper to suit the cutting head and an 8mm shaft to fit the valve guide and cut behind the seats in the head until the seats were also 1.2mm.
Once all that was done, I lappd the valves with fine paste, then assembled with springs and collets and poured fuel into the port to test for leaks.
The last pic shows a piece of dry, clean paper towel held around the edge of the valve by small magnets. The paper towel shows up any leaks.