OK, I SUSPECT that the head gasket has blow. No compression on two cylinders.
Now, if it was the head gasket then I have to ask why. On one hand it might have been chipped away at for months and then finally blown. On the other hand, divving about with the ignition timing might have caused too much advance and that might have done it.
Whatever which way, it's blown (maybe).
It was a happy shopper gasket from my local engine place.
I see two options to increase security for the future.
1) Fit a cometic (aka cosmetic) gasket from SBD. This isn't cheap (£130 by the time postage and VAT is included).
2) Fit a genuine Vaux gasket and assume that the problem was caused by some engine fault or a shoddy gasket
What do you think?