Have they removed the original engine from your bike to determine the fault?
So the admit they didn't test it correctly, they should have put the engine under load by riding it not just revving it.
I'm guessing that the different metals expand with heat, this is why it sounded better cold?
Ask for photo's off the failure if the engine is in pieces.
Engine is still intact on the bike, but with the belt pully cover removed and the sump guard sieve thingie accessed.
I'm past bothering with the dealer. I'll just go to guildford from now on.