Hi all, These exhaust valves were pulled from my Spada, the top (black ones) from the rear cylinder which look ok, and the lower ones from the front cylinder which are clearly not ok. Any clues as to what's happened here? Overheating?
Tight clearances causing the valves to be slightly open during combustion allowing the hot gasses to burn the thin edges of the valve.
Thanks Murdo, There is a definite lip on the underside too from the burnt metal. Two new valves required! Does this damage occur quickly or over time?
Those white deposits are burnt on ash, caused by oil burning in the cylinder. Usual two suspects are rings and valve stem seals. A wire wheel can be used on the face and stem of the valves, just not anywhere near the sealing surface. Try to get a side on look at the valve sealing surface, I had some ZXR valves from a 'servicable' head that very obvious curvature to the seating surface on the valve and a gnarly lip on the margin. The seats were not much better - heavily recessed - head was scrap. You can place the valves in their location with the head upside down and run a finger over the faces. You should be able to feel a recessed valve against a good one.
They may not be scrap yet. Without seeing them I cannot tell from the photo, would need to measure them. Can you take to a machine shop and get them to measure for you?
Thanks. I'll check that out. After cleaning I have now found cracks in the head between the plug socket and the exhaust valves. Not good news.
Those seats look like they will clean up ok. Don't worry about the cracks they are pretty standard. Can be welded if you are concerned.
