I am refurbing the cylinder head on the ST170 engine that is going in my Tiger and have taken the valves out. All the exhaust valves have a 'build up' of an off white substance on the valve face and back of the valve which extends about an inch up the stem.
Does anyone know whether this is a result of the combustion process or some sort of coating deliberately applied....don't want to wire brush it off if it should be there.
Thanks
Ian

Sounds like it just carbon build up just clean them put them in a drill slow speed get some wet and dry paper / sand paper and clean them advise you to wear a
Mask