No – the crack on the side of the worst piston definitely stems from the centre of the crown. The pick-up and deformation around the edge of the crown is a result, not the cause.
I’ll investigate the ring gaps shortly...
I'm drawn to conclude that low-quality pistons are a significant factor, here. Any thoughts on how I can ensure their +20 successors are of suitably Volvo-like quality?
I’ve never owned a car with such distinct valve seat recession. It was significant on the exhaust valves of cylinders one and four. It was occurring at quite a pace – I reset the clearances twice in 3000 miles (of mostly high-speed/high-rpm driving), and they’d closed substantially on these valves. It’s not running lean. It’s suffered a raft of neglect/haplessness in the past, though.
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