This is the buildup I found when I pulled my head which had been totally rebuilt 6 months ago. There was a bad rattling coming from the back of the head which sounded like a loose seat or possibly a bad big end bearing. It turned out to be the buildup on the backside of exhaust valve 4 hitting the air injector. My friend Jim, who helped me with the engine said this buildup is probably from gas additives. That's a lot of crud for roughly 6000 miles on the head. Any ideas on how to avoid this? I've been using BP Premium and a lead additive in the gas because I don't have hardened seats or valves. I had already begun cleaning the #1 exhaust valve in the lower photo, but you can see the buildup on #2, 3 and 4 exhaust valves.


email me with your ideas