The saga continues with my dodgy M54 engine in my E46 CS. The garage who were due to strip the head, rebuild, and refit gave me a call this morning asking me to come down for a quick chat. Got down there and apparently they're unable to do it, they showed me the issues that they were having with the head bolts.
From what I was told and shown, when they took the head bolts off, they put one back in and tried to re-torque it to the BMW specs of 90Nm iirc and it just wasn't having any of it, they did say they could helicoil it but couldn't guarantee how long it would last as the integrity of the actual block was compromised so we agreed that it wasn't worth the cost involved with such a big risk factor involved.
From what I've researched from the internet and speaking to various BMW indies, the heads are notorious for not going back on properly and eventually they'll misfire or leak coolant into the cylinders causing a hydrolock in the worst case scenario.
With that in mind, I've just purchased another M54 engine from a 2004 330 which is showing as having 24k miles on the clock. The block is complete with ancillaries so fingers crossed, I'll have it delivered and fitted this week.
It's been an expensive and stressful few weeks without the car so I'll be glad to have her back on the road and running properly. I'll also be stripping down the old engine and I'll check the valves in the head to see what's gone wrong.