[simonjrwinter]

Thanks guys,

Yes it was the exhaust valve and the banging was the exhaust gasses "farting" (like it!) back through the intake.
I'll check the pushrod, but they're brand new and toughened so hopefully there won't be a problem. I put it back together and it seems to be fine but I'm a bit paranoid about these things you see. Could I have blown the head gasket?

Simon